Ekiras

How to run a Spring Boot Application using Maven/ Gradle

How to start Angular 2 Application on a Custom port other than 4200 You can start the angular project using the angular cli using command ng serve The above command will start the project on port 4200. If you want to start the application on a prot different that 4200 then you can start the project using the following command. ng serve --port <port-number> where <port-number> can be any valid port that is not in use.

Install and Setup Angular Before we start, lets install the angular cli with the following command npm install -g @angular/cli Angular CLI is a tool that can make a new project, compile your typescript files, configure your typescript compiler run your code with live preview, build and package your project. Note Make sure you have latest node and npm installed, at least node version 6.9.x and npm version 3.x.x. To see the versions you can run commands node -v and npm -v for node and npm versions respectively. WarningWhile installation you might get the...

Points to Remember If you are installing node for the first time then, use the NodeSource PPA and first choose the version of node you want to install. Following are the sources for the node versions for Node.js v4 curl -sL https://deb.nodesource.com/setup_4.x | sudo -E bash - for Node.js v5 curl -sL https://deb.nodesource.com/setup_5.x | sudo -E bash - for Node.js v6 curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash - for Node.js v7 curl -sL https://deb.nodesource.com/setup_7.x | sudo -E bash - Once this is done, then update your repositories by command sudo apt-get update Now, finally install NodeJs and Npm using the following command ...

Point to Remember Coercion Operator is used for casting Custom Coercion rules can be applied to a class by defining asType method in a class. Syntax of coercion operator is as What is Coercion Operator Coercion operator is used to do type casting of objects in groovy. It converts objects of one type to another type. Lets take a look at the following examples int a = 123 String s = (String) a The the above example, the assignment of a to s will give a ClassCastException in java but when you run the same in groovy it will...

Ternary Operator Ternary Operator is the short hand of the if-else block, where a condition is evaluated to true or false and following statement is executed. Syntax of the ternary operator is below <boolean expression> ? <executed when condition is true> : <executed when condition is false> A typical example of if-else block is shown below where we check if a variable is null or not. String s = "hello" if( s != null ) println s else println "not found" We can replace the above code with the ternary operator as shown below String s = "hello" println s !=null ? s :...

Points to Remember Default location for gradle dependencies is ~/.gradle or /home/{user}/.gradle. We can specify the location from where to gradle should find dependencies and where it should upload the created artifacts. How to upload an Artifact to a custom location in file system buildscript { repositories { maven { url uri("$buildDir/repo") } } } group 'com.ekiras' version '1.0-SNAPSHOT' apply plugin: 'groovy' apply plugin: 'maven' repositories { mavenCentral() } dependencies { // dependencies } uploadArchives { repositories { mavenDeployer { repository(url: uri("$buildDir/repo")) } } } In the above example, uploadArchives { repositories { mavenDeployer { repository(url: uri("$buildDir/repo")) } } } This tells gradle that it will upload the created...

What is Groovy TruthGroovy has its own way of defining what is true and what is false, this is called the Groovy Truth. In Java, we have to write statements like if(obj ==null), in groovy you can simply write if(obj) and you can define in what conditions this object will evaluate to true and when it will evaluate to false. InfoTo define your custom logic for groovy Truth you need to define methodboolean asBoolean(){ // your logic here} What is True in GroovyFollowing evaluated to true in groovy boolean true Not null objects Non 0 numbers Not null and not...

This post is based on the Gradle Cargo Plugin by bmuschko Include the Plugin You need to include the plugin in your build.gradle. buildscript { repositories { jcenter() } dependencies { classpath 'com.bmuschko:gradle-cargo-plugin:2.2.3' } } apply plugin: 'com.bmuschko.cargo' buildscript block should be the first thing in the build.gradle file. Include the Gradle Cargo plugin dependencies Add the following in your gradledependencies block dependencies { def cargoVersion = '1.4.5' cargo "org.codehaus.cargo:cargo-core-uberjar:$cargoVersion", "org.codehaus.cargo:cargo-ant:$cargoVersion" } Define the Tomcat Container To deploy The war files to Tomcat you need to create a dsl by name cargo and define the mandatory containerId. Note ContainerId will define the version of tomcat you want...

How To Exclude File from a Jar file. Gradle task Jar has a property excludes which takes an array as an input and exclude these files from the Jar file it creates. Let's assume the following directory structure Following example excludes files from the Jar file. task createExcludingFiles(type :Jar){ from ('src'){ excludes = ["main/java/com/ekiras/demo/D.java","main/java/com/ekiras/demo/E.java"] }} This will exclude files D.java, E.java from the jar file. Run the gradle task using command gradle -q createExcludingFiles. The Jar file created will have the following files. META-INF/META-INF/MANIFEST.MFmain/main/java/main/java/com/main/java/com/ekiras/main/java/com/ekiras/demo/main/java/com/ekiras/demo/A.javamain/java/com/ekiras/demo/C.javamain/java/com/ekiras/demo/F.javamain/java/com/ekiras/demo/B.javamain/java/com/ekiras/demo/p1/main/java/com/ekiras/demo/p1/X.javamain/java/com/ekiras/demo/p1/Z.javamain/java/com/ekiras/demo/p1/Y.javatest/test/java/main/resources/test/resources/ Exclude Package in Jar file task createExcludingPackage(type :Jar){ from ('src'){ excludes = ["main/java/com/ekiras/demo/D.java" ,"main/java/com/ekiras/demo/p1/**"] }} Run...

How to start Tomcat on more than one Port. Tomcat settings can be found in TomcatFolder/conf/server.xml file. Root element of the configuration is Server tag. You can add multiple Service under Server tag for running tomcat on more than one port. Default Service Configuration should look as follows <Service name="Catalina"> <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" /> <Engine name="Catalina" defaultHost="localhost"> <Realm className="org.apache.catalina.realm.LockOutRealm"> <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/> </Realm> <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"> <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" prefix="localhost_access_log." suffix=".txt" pattern="%h %l %u %t &quot;%r&quot; %s %b" /> </Host> </Engine> </Service> The above configurations states the folllowing things Service name="Catalina"...

How to change Working Directory of Tomcat to Custom Directory Default Tomcat working directory is webapp. If you want to change this to some other directory then you can follow the steps below. Open the server.xml file. You can find this file in conf/ directory of your tomcat folder. Find the following line in the file <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"> It states the following things name="localhost" - name of the server appBase="webapps" - working directory of tomcat where applications are deployed unpackWARs="true" - if tomcat should unpack war files. autoDeploy="true" - if tomcat should auto deploy changes How to...

Difference Between File, FileCollection and FileTree in Gradle File FileCollection FileTree File is from java.io package FileCollection is from org.gradle.api.file package FileTree is from org.gradle.api.file package File represents a single file. FileCollection represents a collection of files FileTree represents hierarchy of files in a directory or folder. Difference Between File, FileCollection and FileTree Suppose we have a directory structure as shown in image below. We can write a gradle task as shown below task loadFiles(){ doLast{ File file = file('src/main/resources/sample1.txt') println file.name println "\n" FileCollection collection = files('src/main/resources/sample1.txt','src/main/resources/sample2.txt') collection.each { println it.name } println "\n" FileTree tree = fileTree('src') tree.each...

Introduction to FileCollection FileCollection is an interface that extends Iterable<File>, AntBuilderAware and Buildable interfaces. How to load files in a FileCollection Suppose we have a file structure as shown in image below We can load multiple files for operation using the following syntax FileCollection collection = files('relative/path/file1','absolute/path/file2',new File('file3')) As shown in the example above we can load files in three ways From a relative path From a absolute path From a File object. We can write a gradle task to read all files in a folder or directory as follows task fileTree(){ doLast{ FileTree tree = fileTree('src') tree.each { println...

How to check if the operation system is Windows, Linux or Mac Os. org.gradle.internal.os.OperatingSystem is an interface in gradle. This interface provides methods to get th einformation about the operating system. This interface provides the following method to get the information about the operating system. task osInfo(){ doLast{ println OperatingSystem.current(); println OperatingSystem.current().name; println OperatingSystem.current().isLinux(); println OperatingSystem.current().isMacOsX(); println OperatingSystem.current().isWindows(); }} When we run the task with the command gradle -q osInfo it will give the following information. :osInfoLinux 4.4.0-51-generic amd64LinuxtruefalsefalseBUILD SUCCESSFULTotal time: 0.68 secs

How to write a Gradle Task A gradle task can be written in the following two ways task hello(){ doLast(){ println "Hello World" }} Or you can write a task as follows task hello << { println "Hello World"} Here in example 2, << operator is simply an alias for doLast. Write a Gradle Task that depends on another Gadle Task Lets take an example of the following gradle file. build.gradle task openFile(){ doLast{ println "Open file" }}task readFile(dependsOn : 'openFile'){ doLast{ println "Read File" }}task closeFile(dependsOn : ['openFile','readFile']){ doLast{ println "Close File" }} Here in this example, we have...

What is a Gradle Default task ? In gradle, we can have default tasks. A default task is a task that will run if no task is specified. We can define any task a gradle default task using the following defaultTasks 'task1','task2' The defaultTasks takes a list of tasks as a parameter. These tasks will be run if no task is specidied to run. build.gradle defaultTasks 'banner','attribution'task banner(){ doLast { println "______ _ _"; println "| ____| | (_)" println "| |__ | | ___ _ __ __ _ ___ ___ ___ _ __ ___" println "| __| | |/...

How to list all running Gradle Daemon processes To see a list of all the running gradle Daemon processes you can use the following command. gradle --status This will give you a list of all the running processes with their versions as shown in the sample output below. PID STATUS INFO 3461 IDLE 3.0 31881 BUSY 3.0 Here the output is PID - the process id of the gradle daemon process. STATUS - status of the Gradle Daemon, Idle states that this gradle daemon can be used for making builds. BUSY states that it is currently used for running some...

Points to Remember Gradle runs on JVM and several other dependencies. Gradle has to do boootstrap stuff whenever gradle is started. This startup process takes time and makes the build slower. To overcome these points gradle daemon was introduced. What is a Gradle Daemon ? Gradle daemon is a long lived background background process that can be reused for building gradle projects faster. Gradle wrapper saves the time for starting a new gradle instance every time and saves time required for bootstrapping and initialization.Such bootstrap tasks include Initialization of JVM Cache Project information Cache files , tasks Project structures etc...

Point to Remember doFirst() and doLast() are the methods of org.gradle.api.Task interface. Both these methods take a Closure as a parameter. When a task is called this closure is called. A Gradle task is sequence of Action objects and when a task is run all these actions are called in a sequence by calling Action.execute(T) What are doFirst() and doLast() methods in a Gradle task. doFirst(Closure action) This method will add your closure as an action to the beginning of the action sequence. All the code that is written in this closure is executed first when the task is executed....

What is a Gradle Task. Lets first create a gradle file build.gradle with the following contents in it. group 'com.ekiras'version '1.0-SNAPSHOT'apply plugin: 'java'sourceCompatibility = 1.8repositories { mavenCentral()}dependencies { testCompile group: 'junit', name: 'junit', version: '4.11'} Now, lets run the the following command from terminal in the root directory where build.gradle is saved. gradle tasks It will give the list of all the tasks that are defined. It includes both gradle default tasks and custom tasks. Now, you can run any defined task using the command. gradle <task-name> How to write a Custom Task in Gradle. A task in gradle is...

Points To Remember You cannot destroy or terminate the current process not even forcefully. You can destroy a process by using the methods destroy() or forcefully using destroyForcibly(). Read More Java 9 Feature List all processes running on the OS Get the information of the current process Start a new Process and get its Process Id How to get Process Information from Process Id Destroy a running process Destroy a Process There are two methods in interface ProcessHandle that can be used to destroy a process. destroy() - to destroy a process noramally destroyForcibly() - to destroy a process forcefully....

Points to Remember This post used Java 1.9 since ProcessHandle was introduced in Java 1.9. Read More Java 9 Feature List all processes running on the OS Get the information of the current process Start a new Process and get its Process Id How to get Process Information from Process Id Destroy a running process Get the Current Process Information. In this example we will try to get information about the current process. For this we will use the m import java.io.IOException;/** * @author ekiras */public class StartProcess { public static void main(String[] args) { try { Process process =...

Points to Remember Java 9 introduced the new Process Api in java.lang package. ProcessHandle interface can be used to perform operations with processes like start, destroy, list processes. Read More Java 9 Feature List all processes running on the OS Get the information of the current process Start a new Process and get its Process Id How to get Process Information from Process Id Destroy a running process List all Processes running on the OS. To get all the processes running on the OS you can use the static method allProcesses() of the ProcessHandle, this will return a Stream<ProcessHandle> stream...

What is a Module in Java 9 ? Java Modules are a part of Project Jigsaw. A module is a named, self-describing collection of code and data. Its code is organized as a set of packages containing types, i.e., Java classes and interfaces; its data includes resources and other kinds of static information. What are the Type of Modules in Java 9 ? There are two types of Java Modules Java Standard Modules, they start with string java. Java Non-Standard Modules, they start with string jdk. Creating a Custom Module. We can make the following types of modules Module that...

Also Read One To One Mapping Let's create two entities/domains Employee and Department such that they have the following relation between them. Department has-many Employees which means an Employee can belong to only one Department and a Department can have many Employee and Department is the owner of the relation between the two. Owner of the relation means that Owner can exist without the dependent entity but dependent entity cannot stay without the owner entity. Dependent Entity of Relationship will containes the 'foreign key' ID of the Owner entity. In this case, Address will contian the Employee Id in >its...

No sincedb_path set, generating one based on the file path Suppose you have a file at location $PATH/a.csv and we want to read and export data( elastic search server).Let's say you are trying to read this log file through the following configuration input { file { path => ["/some/path/a.csv"] start_position => "beginning" }} So, when you run this for the first time, this will work perfectly. The point to note here is that, when you have run this for the first time, logstash will automatically create a sincedb_path file at your home directory and it might look like .sincedb_1a892d89f927eb484cb12a7b7385ab72. This...

Points To Remember Your Parent class should be annotated with @MappedSuperclass. Follow the Tutorial : How to handle Inheritence with Entities to know how to wrap common properties of entities to a base class. To override any property you musta. Apply the @AttributeOverride annotation on the class that need to override the propertyb. set name property of @AttributeOverride as the name of the field in super class.c. set the column property of @AttributeOverride to override the column definition of the attribute. Let's say our Base class looks as follows package com.ekiras.domain.base;import javax.persistence.*;import java.util.Date;/*** @author ekiras*/@MappedSuperclasspublic abstract class BaseDomain { @Id...

How to create a jar file. We can make a jar file with a single class using the following commands Here can be replaced by the name of the jar file you want. 1. Create a jar file with single file jar --create --file=<FileName> <file-1> 2. Create a jar file with multiple files jar --create --file=<FileName> <file-1> <file-2> 3. Create a jar file with all files in a directory jar --create --file="<FileName> -C /path/to/dir/ ." Here -C specifies the directory and . specifies that it need to include all the files in te directory. Some of the shorthands for the...

findAll() This method will find all the items in the groovy collection that matches the IDENTITY closure. collect() This method iterates through a collection and transforms each entry element to a new element using IDENTITY closure as a transformer. It returns a new collection of elements copied from the original collection. Difference between finalAll() and collect() methods findAll() collect() findAll() will return the collection or subset of collection that satisfy the Identity closure or a condition collect() will return a new collection or sub set of collection. findAll() will not modify the entry elements of the collection collect() will modify...

Spring Boot : IntroductionSpring Boot can be referred as Spring on Steroids. Spring boot is a wrapper written over spring modules to allow users to create fast paced spring applications without doing the redundent configurations needed to setup the application.Features provided by Spring Boot CLI applications - enables to create a single class application. Embedded Tomcat and Jetty Auto configurations for most of the libraries like mysql, mongo, amqp etc No Xml required for setup or configurations. Ability to package the application as both war and jar. Dependency Management using starter projects and BOM's. For example, When you create a spring application...

Problem Statement You are given an array where each element follows the rule that given any index, the number at that index will either be  +1 of the number at that index. +0 of the number at that index. -1 of the number at that index. Suppose the array is  Sample Input arr       = {1,2,3,2,3,4,5,6,7,6,5,4,5,6,4,4,4,4}; search = 5 Sample Output 6  (First occurrence of search ) Sample Input arr       = {1,2,1,2,1,2,1,2,1,2}; search = 5 Sample Output 1  ( Element is not found in the array) Algorithm Star iterating from start of the array. Check if the value...

What are Profiles in Spring BootProfiles can be seen as different environments in spring boot application. Suppose you are working on an application where you have different staging environments like Dev, QA, UAT, Production etc. So you will have different configurations for each environment, for this kind of applications what you need is having different values that can be switched depending upon some flags. In early days, people used to write configurations for all environments and comment the unused environments. But with Spring Boot we can do this without commenting any code by use of Profiles. Suppose we have database...

How to write to the beginning of a file using shell script in LinuxSuppose, we have a file release.txt and we want to write to first line of the of the file whenever a new release is made. sed -i '1i\'"text to write " filename Using the above command as sed -i '1i\'"newVersion-RELEASE" release.txtThis will append the text to the first line of the file release.txt In the example shown above , we have added a new version 2.0.0-RELEASE to version.txt file .If you want to do this using a shell script then you can do it as follows #!/bin/bashfunction writeAtBeginning(){...

How to disable Session Creation for Stateless AuthenticationWe need to disable session creation for authenticating requests based on token based authentication.This can be easily configured by the following configurations. view plaincopy to clipboardprint? package com.ekiras.ss.security.config;      import com.ekiras.ss.security.filter.TokenAuthenticationFilter;   import org.springframework.context.annotation.Bean;   import org.springframework.core.Ordered;   import org.springframework.core.annotation.Order;   import org.springframework.security.config.annotation.web.builders.HttpSecurity;   import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;   import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;   import org.springframework.security.config.http.SessionCreationPolicy;   import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;      /**   * @author ekansh   * @since 11/4/16   */   @EnableWebSecurity   @Order(Ordered.LOWEST_PRECEDENCE-100)   public class RestSecurityConfigurerAdapter extends WebSecurityConfigurerAdapter {          @Override       protected void configure(HttpSecurity http) throws Exception {              http.sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS);          }               }   package com.ekiras.ss.security.config; import com.ekiras.ss.security.filter.TokenAuthenticationFilter; import org.springframework.context.annotation.Bean; import org.springframework.core.Ordered; import org.springframework.core.annotation.Order; import org.springframework.security.config.annotation.web.builders.HttpSecurity; import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity; import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter; import org.springframework.security.config.http.SessionCreationPolicy; import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter; /** * @author ekansh * @since 11/4/16 */ @EnableWebSecurity @Order(Ordered.LOWEST_PRECEDENCE-100) public class RestSecurityConfigurerAdapter extends WebSecurityConfigurerAdapter {...

Create Database Schema and tables First we will create a Database Schema as shown in the image below. We have to create 3 Tables in database. user - to hold the user data. role - to hold the data of roles that a user can have. user_roles - to hold the mapping of user and roles. Configure JDBC Authetication using MYSQL Query. Step 1 : Add the Dependencies compile('org.springframework.boot:spring-boot-starter-data-jpa') runtime('mysql:mysql-connector-java') Step 2 : Add the Datasource properties spring.jpa.hibernate.ddl-auto=updatespring.datasource.url=jdbc:mysql://localhost/demo_ssspring.datasource.username=rootspring.datasource.password=rootspring.datasource.driver-class-name=com.mysql.jdbc.Driverspring.datasource.maxActive=10spring.datasource.max-idle=4spring.datasource.min-idle=2spring.datasource.test-while-idle=truespring.datasource.test-on-borrow=truespring.datasource.validation-query=SELECT 1spring.datasource.time-between-eviction-runs-millis=60000spring.datasource.min-evictable-idle-time-millis=300000spring.jpa.properties.hibernate.current_session_context_class=org.springframework.orm.hibernate4.SpringSessionContext Step 3 : Add the Datasource Bean to SpringSecurity Configurer class @Autowired private DataSource dataSource; Add queries to be fired for...

Implement Role Hierarchy with In-Memory Authentication In order to configure role hierarchy, you need to make a bean RoleHierarchy define a expressionhandler to read role hierarchy package com.ekiras.ss.config;import org.springframework.context.annotation.Bean;import org.springframework.security.access.expression.SecurityExpressionHandler;import org.springframework.security.access.hierarchicalroles.RoleHierarchy;import org.springframework.security.access.hierarchicalroles.RoleHierarchyImpl;import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;import org.springframework.security.config.annotation.web.builders.HttpSecurity;import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;import org.springframework.security.web.FilterInvocation;import org.springframework.security.web.access.expression.DefaultWebSecurityExpressionHandler;/** * @author ekiras */@EnableWebSecuritypublic class SpringSecurityConfigurer extends WebSecurityConfigurerAdapter{ private SecurityExpressionHandler<filterinvocation> webExpressionHandler() { DefaultWebSecurityExpressionHandler defaultWebSecurityExpressionHandler = new DefaultWebSecurityExpressionHandler(); defaultWebSecurityExpressionHandler.setRoleHierarchy(roleHierarchy()); return defaultWebSecurityExpressionHandler; } @Bean public RoleHierarchy roleHierarchy(){ RoleHierarchyImpl roleHierarchy = new RoleHierarchyImpl(); roleHierarchy.setHierarchy("ADMIN > USER"); return roleHierarchy; } @Override protected void configure(AuthenticationManagerBuilder auth) throws Exception { auth.inMemoryAuthentication() .withUser("ekansh") .password("password") .authorities("USER", "ROLE"); auth.inMemoryAuthentication() .withUser("admin") .password("admin") .authorities("ADMIN"); } @Override protected void configure(HttpSecurity http) throws Exception {...

How to integrate Spring Security with Spring boot Add the following dependency in your build.gradle compile('org.springframework.boot:spring-boot-starter-security') Basic Spring Security Configurations Add the dependency in your build.gradle Run your application gradle bootRun for gradle and mvn spring:run for maven The default username is user and the password will be printed in the logs as shown in the image above. So in this case you can login using username = userpassword = // printed in logs Note A new password will be created each time the application restarts. Spring Security Configurations with defined username and password Add the following in your application.properties...

Points To Remember Add the SessionFactory bean in the Application class. Add the Current Session Context class in application.properties. Use the SessionFactory using @Autowired annotation. How to Configure & Use SessionFactory Bean

Points To Remember There are three ways to do exception handling in spring boot application. Global Level using -  @ControllerAdvice Controller Level using - @ExceptionHandler  Method Level using - try/catch   Difference between @ExceptionHandler and @ControllerAdvice How to do Exception Handling in Rest Application To demonstrate Exception Handling we will make three Exceptions. BaseException that will be parent of all the Custom Exceptions. CustomException1 that extends Base Exception. CustomException2 that extends Base Exception. We will create the following methods ex1() throws BaseException ex2() throws CustomException1 ex3() throws CustomException2 ex4() throws NullPointerException  ex5() throws NumberFormatException and now we will see how we can handle these exceptions using above...

Adding Custom Banner in Spring Boot ApplicationYou can replace the default spring boot banner for your application to give a more meaningful name to it. Steps to add Custom Banner in application. Go to the link ASCII art generator and generate an ascii art. Create a file named banner.txt under resources folder. That's it, rerun your application and you will be able to see your new banner. Note :: name of the file should be banner.txt and placed in folder resources Note :: How to disable the banner in Spring boot Application.

Points To RememberAccept the Locale from Headers e.g @RequestHeader("Accept-Language") Locale locale Step 1 : Define Beans for InternationalizationAdd the files in resources/i18n folder as shown in image Add the following to the Application class ( The main class) @Bean public LocaleResolver localeResolver() { SessionLocaleResolver slr = new SessionLocaleResolver(); slr.setDefaultLocale(Locale.US); // Set default Locale as US return slr; } @Bean public ResourceBundleMessageSource messageSource() { ResourceBundleMessageSource source = new ResourceBundleMessageSource(); source.setBasenames("i18n/messages"); // name of the resource bundle source.setUseCodeAsDefaultMessage(true); return source; } Now inject the MessageSource Bean where you want to internationalize the message. We will be doing it in the Controller. Note...

Binding data from URL to a variable Suppose you want to have bind some data from URL then you can do the following create the @RequestMapping annotation e.g /list/{id} /{version}/list/{id} bind the Url parameters using @PathVariable annotation e.g @PathVariable("id") Long id @PathVariable("version") int version,@PathVariable("id") Long id Complete code may look like this, @RequestMapping("list/{id}") public Object list(@PathVariable("id") Long id ){ // Logic goes here } @RequestMapping("/{version}/list/{id}") public Object list(@PathVariable("version") int version,@PathVariable("id") Long id ){ // Logic goes here }

How to find a Random Number Between two given Numbers Suppose we want to generate a number between two given numbers X and Y then we can use the following two approaches. Approach 1 Generate a random number between 0 to (Y - X ) just add this to X. i.e X+N For, example if we have to calculate a random number between 100 and 150, then in that case X = 100 , Y = 150,Then we calculate a number between 0 to (150-100)  i.e  0 to 50. Thus, we just need to add this to 100 to get...

How to Make a Http GET request and read responseSteps to make a HTTP GET request Make URL object. Make HttpURLConnection object from URL object and type cast it to HttpURLConnection Set Request method to GET. Add Headers using method setRequestProperty() if required. Use BufferedReader to read the input stream of the connection. Read the response from buffered reader object. The code to implement the above steps is shown below.

How to make enums inside java classYou can use enums inside a class as shown in the code below. User.Gender.MALE or FEMALE is always associated with the user property. However if you need Gender to be generic and u want to use it with animals also, then you might want to keep this enum in a separate class. package com.ekiras.demo;public class User { public enum Gender{ MALE, FEMALE } private String name; private String address; private String email; private String password; private Gender gender = Gender.MALE; } You can also use the enums with parameters inside class as shown below. package...

Points To Remember Add dependency of spring security Add custom username password in application.properties A unique password is generated each time application is started if no authentication process is specified. You can configure your own authentication  providers, managers, filters, entry points, tokens etc as required. Getting started with Spring Security and Spring BootIn order to apply Spring Security to a Spring Boot application, firstly you need to add the dependency in the application as follows In Maven you can do it as follows. <dependencies> <dependency> <groupId>org.springframework.security</groupId> <artifactId>spring-security-web</artifactId> <version>4.0.3.RELEASE</version> </dependency></dependencies> In Gradle you can do it as follows. dependencies { compile...

What is Hoisting in Javascript ??In Javascript the variable declaration can be done at any place inside the function or inside the script. Where a variable is declared makes no difference because the javascript interpreter always move the variable declarations silently to the top of the scope where the variable is used.For example, everyone will be fine the following javascript code. <script> var num; num = 5; function foo(){ alert(num); } foo(); </script> And, all will be able to guess that the function foo() will alert value 5. However, the following code will confuse a lot of the developers, since...

Points To Remember You can create objects of a function in javascript. Function can have both private and public methods. Functions can inherit other functions Create an Object in JavascriptLet us create a User object in javascript. var User = function() { _self = this; var _name; _self.getName = function() { return _name; } _self.setName = function(name) { _name = name; } _self.toString = function() { return "Person{name::" + _name + "}"; }} Here User is a function name is a private variable and will not be accessible outside the User function. _self is used to save the this reference, this...

Following are the steps to setup to Hazelcast server Put data in hazelcast Retrieve data from hazelcast Step 1 : Add the Hazelcast dependency compile("com.hazelcast:hazelcast:3.3.5") compile("com.hazelcast:hazelcast-client:3.3.5") Step 2 : Initialize the Hazelcast Instance (Hazelcast Server) Config config = new XmlConfigBuilder().build();HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance(config); The above code will start the Hazelcast server with default settings. For more settings you can refer this blog. Step 3 : Connect to Hazelcast server using a Hazelcast ClientNow to need to get a Hazelcast client to get and post data to the hazelcast server. Following is an example of how to get the hazelcast client....

Steps : How to register a Filter in the Application Make a class. Make it a spring bean by using @Component annotation. Implement Filter interface to register it as a Filter in the Filter chain. Use @Order annotation to define the order of the filter in the filter chain. Following is the example of how you can implement the Filter using the above mentioned steps

Points To Remember You can use Reflection to check if the field of a class is static or not. You need to get the modifiers of the field to check if the field is static. How to check if the field of a class is static by ReflectionThe following is the only way to check if the field is static or not field.getModifiers()& Modifier.STATIC) == Modifier.STATIC Following program shows how to get the static fields from a class. package com.ekiras.demo;import java.lang.reflect.Field;import java.lang.reflect.Modifier;public class Test { public static void main(String args[]){ Field[] fields = Person.class.getDeclaredFields(); for(Field field : fields){ if((field.getModifiers()& Modifier.STATIC) ==...

When Exception in thread "main" java.util.ConcurrentModificationException occurs. package com.ekiras.demo;import java.util.ArrayList;import java.util.List;public class Test { public static void main(String args[]){ // create a new list List<String> list = new ArrayList<String>(); // add 50 items to the list for(int itr=0;itr<50;itr++) list.add("user-"+(itr+1)); // try to remove item from list while iterating the list for(String str : list){ if(str.equals("user-15")){ list.remove(str); } } } } The above code will give the following error. Exception in thread "main" java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859) at java.util.ArrayList$Itr.next(ArrayList.java:831) at testing.Test.main(Test.java:18) How to avoid ConcurrentModificationException Create the list of type CopyOnWriteArrayList, this will create a new copy of list for every operation performed...

Points To Remember This error occurs when Server does not allow cross domain headers. Application does not allow cross domain headers. Custom headers provided by request is not accepted by the application. How to Solve : No 'Access-Control-Allow-Origin' Access-Control-Allow-Origin error In order to allow cross domain ajax calls to your Server you need to allow the Cross Domian Headers in your application. You can allow the cross domain requests from your application in Spring boot by adding a CORS Filter as shown below. response.setHeader("Access-Control-Allow-Origin", "*");response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");response.setHeader("Access-Control-Max-Age", "3600");response.setHeader("Access-Control-Allow-Headers", "Content-Type, x-requested-with, X-Custom-Header"); Here you need to specify the following Headers...

Points To RememberThere are two attributes for a View in android to align its content gravity layout_gravity The basic difference between the two is that android:gravity is used for child elements of the view. android:gravity_layout is used for this element with respect to parent view. So, if you have a layout like <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" > <TextView android:layout_width="match_parent" android:layout_height="50dp" android:text="EkiRas" android:textSize="22dp" android:gravity="center" /> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_gravity="center" > // Other Elements </LinearLayout></LinearLayout> In the above code, outer LinearLayout will set its child elements in center. TextView gravity:center will set its ocntent in center. inner LinearLayout will be aligned in the center...

Points To RememberYou need to add the following dependency to your project to use Spring Rest Template. compile('org.springframework:spring-web:3.0.2.RELEASE') How to get response from a server by HTTP GET callFollowing are the methods that can be used to get the response from a url using HTTP GET method. getForObject() This method takes a URL, Response class (it tells that the response should be bound to this class). RestTemplate restTemplate = new RestTemplate();String response = restTemplate.getForObject("http://localhost:8080/someUrl",String.class); Following method will make a Http GET call with params. Map<String,String> params = new LinkedHashMap<String, String>();params.put("userId","1"); RestTemplate restTemplate = new RestTemplate();String response = restTemplate.getForObject("http://localhost:8080/someUrl",String.class,params); This method does...

Points To Remember You need to create a ListView in your activity. Then create a view for Item of the ListView. Create an Adapter and a list of objects to display. Pass the List of objects to the ListView. How to create a Basic List View Your Activity may look like the following activity_main.xml <?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <TextView android:layout_width="match_parent" android:layout_height="50dp" android:text="Planet List" android:textAlignment="center" android:textSize="24dp" /> <ListView android:id="@+id/list_view_drawer" android:layout_marginTop="50dp" android:layout_width="match_parent" android:layout_height="wrap_content" android:dividerHeight="1dp" android:divider="@android:color/holo_blue_light" xmlns:android="http://schemas.android.com/apk/res/android" /></RelativeLayout> Your item may look like the following list_view_item.xml <?xml version="1.0" encoding="utf-8"?><TextView android:layout_height="50dp" android:textAlignment="gravity" android:textColor="@android:color/holo_blue_dark" android:paddingLeft="15dp" android:layout_centerVertical="true" android:layout_centerHorizontal="true" android:gravity="center_vertical" android:layout_width="wrap_content" xmlns:android="http://schemas.android.com/apk/res/android" /> Your...

Points To Remember You need to create a file in res > menu > menu.xml You can use showAsAction property to decide if to show the action icon on action bar or not.  Adding Action Icon Action button on Action BarYou can choose either of the following app:showAsAction="never" This will show the action in the list view when menu icon is pressed. app:showAsAction="ifRoom" This will show the action in the action bar if the amount of space required to show the action is available on the Action bar. <menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" tools:context=".HomeActivity"> <item android:id="@+id/action_settings" android:orderInCategory="100" android:title="#Settings" app:showAsAction="never" /> <item...

Points To RememberBy default all the fields in the Hibernate Entity are updatable and insertable. To make a field non updatable in hibernate you nee to add the annotation @Column(updatable = false) Make a field Non Updatable in an Hibernate EntitySuppose you have a User class and you want to make email as a non updatable field, all you need to do is add the @Column(updatable = false) annotation as shown in the example below. @Entitypublic class User { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @Column(name = "email",updatable = false, nullable = false, unique = true) private String email; // GETTERS and...

Points To RememberYou can use the Environment interface in package org.springframework.core.env to get the current profiles in spring application.You can make use of the following methods to get the information about the profiles. acceptsProfiles(String ...profiles) - returns if the profiles given in input is active. getActiveProfiles() - Gives a list of profiles explicitly made active for this enviornment. getDefaultProfiles() - gives a set of profiles to be active by default if no active profile is set explicitly. See how to set and configure profiles in spring.Must Read :: What are profiles in Spring boot. How to get Active Profiles in an EnvironmentAll you need...

How to allow cross origin ajax calls to Spring application Add the following class to your Spring or Spring Boot application. After adding this class you will be able to make ajax calls to your application. package com.ekiras.filter;import org.springframework.stereotype.Component;import javax.servlet.*;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@Componentpublic class CorsFilter implements Filter { public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletResponse response = (HttpServletResponse) res; response.setHeader("Access-Control-Allow-Origin", "*"); response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE"); response.setHeader("Access-Control-Max-Age", "3600"); response.setHeader("Access-Control-Allow-Headers", "x-requested-with"); chain.doFilter(req, res); } public void init(FilterConfig filterConfig) {} public void destroy() {}} Now you can hit the ajax calls like following $.ajax({ method:'GET', url:'http://someurl', success:function(data){...

How to get List of records in Hibernate // List all records public List<User> list(){ return sessionFactory.getCurrentSession() .createCriteria(User.class).list(); // List all records } // List records based on MAX public List<User> list(Integer max){ return sessionFactory.getCurrentSession().createCriteria(User.class) .setMaxResults(max).list(); } // List records with MAX records and OFFSET public List<User> list(Integer max, Integer offset){ return sessionFactory.getCurrentSession().createCriteria(User.class) .setMaxResults(max) .setFirstResult(offset) .list(); } // List records with MAX records and OFFSET and ORDER by id field of User class public List<User> list(Integer max, Integer offset){ return sessionFactory.getCurrentSession().createCriteria(User.class) .setMaxResults(max) .setFirstResult(offset) .addOrder(Order.asc("id")) .list(); } this is body.

Points To Remember @Column annotation is used to define the column name, type, constraints. It should be used with the fields either above the getter or above field declaration. The @Column annotation can take the following configuration. Property Type Default Value Description name Optional "" The name of the column. Defaults to the property or field name unique Optional false Whether the column is a unique key. nullable Optional true Whether the database column is nullable. insertable Optional true Whether the column is included in SQL INSERT statements generated by the persistence provider. updatable Optional true Whether the column is included...

How to use @Entity annotation in HibernateSuppose we want to make a User domain with the following fields Id Name Age Address Gender Email Mobile We can create tell the hibernate to register this Domain class as a Hibernate Entity object by adding @Entity annotation at the class level. package com.ekiras.domian;import com.ekiras.enums.Gender;import javax.persistence.Entity;@Entitypublic class User { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; private String name; private Integer age; private String address; private Gender gender; private String email; private Long mobile; // GETTERS and SETTERS} So what the above line means is that, hibernate treats the class User as a Hibernate Persistence Entity....

Algorithm UsedWe will be using the following algorithm to find all the permutations of a string Take the first letter as a prefix and find all the permutations of the remaining string. Each of the prefix will also be a permutation itself. If you want to find all the permutations of string with same length as the original string then skip the prefix's as the combination. public class Permute { static String codes = "eki"; static int count; public static void main(String args[]) { permute("", codes); System.out.println(">>>>>>>" + count); } public static void permute(String prefix, String str) { System.out.println(prefix); count++;...

This is a sample Spring Boot Application that uses  JDBC Mysql JPA MVC Gradle Create Basic CRUD for Person Entity with JPA and Mysql Download from GitHub Project Structure  build.gradleView Maven Dependencies (pom.xml) here. buildscript { ext { springBootVersion = '1.2.5.RELEASE' } repositories { maven { url "http://repo.spring.io/libs-milestone" } mavenCentral() } dependencies { classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}") classpath("io.spring.gradle:dependency-management-plugin:0.5.1.RELEASE") }}apply plugin: 'java'apply plugin: 'eclipse-wtp'apply plugin: 'idea'apply plugin: 'spring-boot' apply plugin: 'io.spring.dependency-management' apply plugin: 'war'war { baseName = 'springboot' version = '0.0.1-SNAPSHOT'}sourceCompatibility = 1.7targetCompatibility = 1.7repositories { mavenCentral() maven { url "http://repo.spring.io/libs-milestone" }}configurations { providedRuntime}dependencies { compile("org.springframework.boot:spring-boot-starter-data-jpa") compile("javax.servlet:jstl:1.2") runtime("mysql:mysql-connector-java") compile("org.springframework.boot:spring-boot-starter-jdbc") compile ("org.springframework.boot:spring-boot-starter-web") providedRuntime("org.springframework.boot:spring-boot-starter-tomcat") providedRuntime 'org.apache.tomcat.embed:tomcat-embed-jasper'}eclipse...

Points To RememberYou can make the cli application without writing any configurations or xml's that you needed to do in traditional spring framework.Spring boot automatically adds the boiler plate code to the application that may look like this // import org.springframework.web.bind.annotation.Controller// other imports ...// @Grab("org.springframework.boot:spring-boot-web-starter:0.5.0")// @EnableAutoConfiguration@RestController@RequestMapping("/")class Hello { @RequestMapping(value="/hello") public String index(){ return "<h1>Hello World !! Today's date is " + new Date() + "</h1>"; }// public static void main(String[] args) {// SpringApplication.run(Example.class, args);// }} The following code is a self sufficient code to run in a servlet container. Hello.java import java.util.Date;@RestController@RequestMapping(value="/")class Hello{ @RequestMapping(value="/hello") public String index(){ return "<h1>Hello World...

Points To Remember@Table Annotation is an annotation that is used to give the table level information. It can be uesd to specify the following Table name (optional,default ="")- to set the name of the table in database Table schema (optional,default ="")- to set the schema of the table in database Table catalog (optional,default ="") -to set the catalog of the table Table Constraints (optional,default = []) to set the constraints on the table. It belongs to the package javax.persistence.Table @Table(name="person",schema="ekiras",uniqueConstraints = {@UniqueConstraint(columnNames = {"id","email"})})public class Person { private Long id; private String name; private String email; // code} If you do not define the name property of...

How to remove nulls from a List in Java One way is to iterate the objects from the Collection ( like List, Array, Map etc) and remove null objects. Remove a particular object from List, Array or Map by searching the object and then removing it. Using the Collections.singleton(T o) method from the java.util package and then it will remove all the objects from the collection. Removing Objects in Traditional Way.We will be taking the following list of String for all our Examples String init[] = { "One", "Two", "One", "Three", "One", "Two", "Three","Four", "Two" }; Here we will remove the objects...

Points To Remember You should pass the params separated by "/". You can pass the params to the controller and pass them to the templates or apply logic. You need to add $routeParams input to your controller function to get these params. How to pass Params from one state to another in AngularJs using ngRoute.You need to add the route params along with the url e.g you can send the params as follows #url/param1/param2 This is how you can update your $routeProvider to use these route params. Finally, access the params in the controller and pass them to the template....

Points To Remember You can handle all types of runtime exceptions and custom exceptions using @ExceptionHandler annotation.  You just need to define the class to the annotation to handle exceptions of that class. Spring MVC handle Exceptions in ControllerHere we have a simple Spring MVC application with the following. HomeController wih three actions  throw1 - throws Custom exception throw2 - throws Custom exception throw3 - throws Runtime exception Home Controller package com.ekiras.controller;import java.text.DateFormat;import java.util.Date;import java.util.Locale;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.stereotype.Controller;import org.springframework.ui.Model;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestMethod;import org.springframework.web.bind.annotation.ResponseBody;import com.ekiras.exception.MyException;import com.ekiras.exception.MyGlobalException;@Controllerpublic class HomeController { private static final Logger logger = LoggerFactory.getLogger(HomeController.class); @RequestMapping(value = "/", method = RequestMethod.GET) public...

When I was looking for a cheap and best smartphone, then Asus Zenphone 2 is the one that comes in choice which comes in half the price of all top-tier smart phones and luckily nowhere near half the quality.  There are many features that makes this phone desirable like: 1) Design: The luxurious ultra thin lollipop based Asus phone featured a hard plastic chassis available in multiple colors that make the phone even more desirable for me. the 72 % screen to body ratio and 1920 x 1080 full HD IPS display maximises the viewing experience. The removable back-panel gives access to...

Points To RememberYou need to check the following things fro creating the nested folders If it is a directory by method isDirectory() If it exists by method exists() You might need to check if you have write permissions to create folder by method canWrite() How to create Nested Folders/Directories in JavaThis is how yo can create the nested folders in java. CreateNestedFolders.java import java.io.*;class CreateNestedFolders{ public static void main(String args[]){ File file = new File("/home/ekansh/test/1/2/3/abc"); if(!file.canWrite()){ // check if user have write permissions if(!(file.exists() && file.isDirectory())){ if(file.mkdirs()) System.out.println("Success ! Folders created."); else System.out.println("Failure ! Folders not created."); } }else{ System.out.println("PERMISSION DENIED");...

Points To Remember TimerTask is a class that can run a Thread repeatedly after a specific period. You can either implement your own class also by implementing Runnable Interface. Then you may need to put your thread to sleep and then resume the thread after a desired interval. The TimerTask will do this more efficiently for you then implementing your own code. How to schedule a Thread to run after fixed intervalWe will be using TimerTask to schedule the Thread after every 1 sec. TimerTask class in Java implements Runnable interface and has the following methods. cancel - to cancel the...

Setting up AngularJS.All you need to do is Download the AngularJs script from https://angularjs.org/. You can use the AngularJs cdn   http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js Add the Angular Js ng-app="" tag to initialize the angukar application. Add the angularjs script to the Html page and you are good to go <!DOCTYPE html><html>  <head>    <link rel="stylesheet" href="style.css">    <script src="script.js"></script>    <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.15/angular.min.js"></script>  </head>  <body ng-app="">    <h1>{{"Hello" +" " + "World!" }}</h1>  </body></html> The above code will give you the following output. Loading plunk...

Apple is one of the best selling brands across the world. Some of the trending products of Apple in the year 2015 are. Apple Watch Some of the key features of the watch are  Stainless Steel case Sapphire crystal Ceramic back Heart Rate sensor, Accelerometer and gyroscope Requires iphone 5+ for operation. Why to buy Apple watch The Apple Watch is coming in six different versions: there's the Apple Watch, the Apple Watch Sport and the Apple Watch Edition. And each of these comes in two sizes, for those that like a larger or smaller device for their wrist. Its neither...

Acer Laptops When we talk about the Laptops for beginners or entry level laptops some of the best brands that offer these are ACER, HP, Lenovo, Samsung. Laptops are meant to give you a multifunctional computer. They have built-in Wi-Fi1 to give you the freedom to work and play wirelessly. Depending on the model, larger screen sizes, bigger hard drives and built-in DVD drives increase laptops' weight, which makes them less portable than netbooks but an excellent choice for your everyday computing needs.   And thankfully if you know where to look, it's possible to get a sleek and impressive...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Which of these method of Thread class is used to find out the priority given to a thread? get() ThreadPriority() getPriority() getThreadPriority() C In the following example, which class must be abstract: abstract class X implements Y { // implements all but...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds What is the output of this program? class exception_handling { public static void main(String args[]) { try { int i, sum; sum = 10; for (i = -1; i sum = (sum / i); } catch(ArithmeticException e) { System.out.print("0"); } System.out.print(sum); }...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Which of these interface is implemented by Thread class? Runnable Connections Set MapConnections A What is the output of this program? class area { int width; int length; int area; void area(int width, int length) { this.width = width; this.length = length;...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Which of the following statements are incorrect? public members of class can be accessed by any code in the program. private members of class can only be accessed by other members of the class. protected members of a class can be inherited...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Which of the following statements are false in the concept of abstract classes: Can b instantiated It may or may not include abstract methods It can be subclassed None of the above A Which of these is static variable defined in Collections?...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds What is the output of this program? class newthread extends Thread { Thread t; newthread() { t1 = new Thread(this,"Thread_1"); t2 = new Thread(this,"Thread_2"); t1.start(); t2.start(); } public void run() { t2.setPriority(Thread.MAX_PRIORITY); System.out.print(t1.equals(t2)); } } class multithreaded_programing { public static void main(String...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Given the class definitions System.out.print(b.display() + " ");System.out.print(d.display() + " ");System.out.print(bd.display() + " ");System.out.println(); will display: Base Derived Derived Base Base Derived Base Derived Base Derived Derived Derived A Which of the following keywords are used to control access to a class...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Class A      {       public static void main(String a1[])       {         String s1= ?Hello?;         StringBuffer s2= new StringBuffer(?Hello?);         s1 = s1 + ?World?;         s2.append(?World?);       }      }   In the above code how many String and StringBuffer objects are created? 1 & 1 2 & 1 2 & 2 1 & 2 B Difference between String and StringBuffer object is...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds What is the output of this program? class box { int width; int height; int length; } class mainclass { public static void main(String args[]) { box obj1 = new box(); box obj2 = new box(); obj1.height = 1; obj1.length = 2;...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Which of the following is incorrect statement about packages? Interfaces specifies what class must do but not how it does. Interfaces are specified public if they are to be accessed by any code in the program. All variables in interface are implicitly...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds Which of these keywords is used to manually throw an exception? catch finally throw try C What is the output of this program? class access{ public int x; private int y; void cal(int a, int b){ x = a + 1; y...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes :seconds What is the order of precedence (highest to lowest) of following operators? 1. & 2. ^ 3. ?: 1 -> 2 -> 3 2 -> 1 -> 3 3 -> 2 -> 1 2 -> 3 -> 1 A What is the...

Suppose you have a dump of more than one databases in a single dump file, then you can restore one or all the databases. mysql -u root -p --one-database DBNAME < DUMPFILE.SQL You should take care of a few things when you take the dump. Create a database by that name in mysql if it does not exist. Switch to the database you want to restore, this will help restore the database properly. You need to be outside mysql environment to run this command. For more specific restoration of databases from a dump file you can try mydumpsplitter. 

Points To Remember You need to use SCE to render html as it is on the page. There are two ways to use sce either you use it in the angular controller to prevent escape html or you can create a filter to do this where ever you need it. Using it with a filter is a much better way to do so, if you need to do it at multiple places. Following Plunker example shows how you can prevent escaping of Html Loading plunk... Prevent Escape Html from angularjs Controllers <html><head><script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.2.15/angular.min.js"></script></head><body ng-app="demo"><div ng-controller="home"> Original Text : {{text}}<br/><br /><br /> EscapedText...

Syntax to get List of domain Object list can be used on the Criteria object as shown below. criteria.list() How to get a List of a Domain class using Hibernate's Criteria Query.If we have a domain class Category as shown below. Catgeory.class package com.ekiras.domain;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.OneToMany;import javax.persistence.Table;@Entity@Table(name="category")public class Category { public Category(){} public Category(Long id){ this.id = id; } public Category(Long id, String name){ this.id = id; this.name = name; } @Id @Column(nullable=false, name="id") @GeneratedValue(strategy=GenerationType.AUTO) private Long id; @Column(nullable=false, name="name") private String name; // Getters and Setters } We can get the list of all the categories...

Points To Remember Create a Pagination Taglib using this example. Add Bootstrap css and js in the jsp you want to do pagination and include the taglib in the jsp. Pagination in Spring Hibernate Application using Bootstrap Create a Domain Person. Create a Service PersonService Create a Dao PersonDao. Create a Controller PersonController. Create a Taglib PaginationTaglib. Person.java package com.ekiras.domain;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name="person")public class Person { public Person(){}; public Person(String name,Integer age){ this.name = name; this.age = age; } @Id @GeneratedValue(strategy=GenerationType.AUTO) @Column(name="id") private Long id; @Column(name="name") private String name; @Column(name="age") private Integer age; // GETTERS and SETTERS...

Points To RememberBootstrap is one of the major UI componnet used worldwide, So you may want to implemnt pagination using bootstrap in java , j2ee or spring application. So all you need to do is Create a Class that will behave like a taglib. Create a Tld file that will map the tablib class with the jsp's. Use the taglib on jsp using the tld file. Create Pagination Taglib for Jsp with Bootstrap.Following is an example of the a custom taglib built for Bootstrap. This taglib takes in uri -> action to be hit when clicked. offset -> the offset...

Points To Remember NoClassDefFoundException is an Exception that occurs when a class is not found at runtime but was available at compile time. This exception is different from ClassNotFoundException. See the differences here. Example : Creating a NoClassDefFoundExceptionSuppose we have two classes A and Test. We just make an object of class A in Test class. A.java class A{ public A(){ System.out.println("This is class A"); }} Test.java class Test{ public static void main(String args[]){ System.out.println("This is Test Class"); A obj = new A(); }} The output of the program will be as follows This is Test ClassThis is class A...

Points To Remember

Points To Remember Enums are special java classes that are used to declare constants and methods. Enums have all the variables declared as public static final. Enums variables can be compared using == operator. End of a enum can be declared by a semi colon, but this is optional. There are two ways to use Enums  ORDINAL (saves the enum values in integer format starting from 0.) STRING (saves the enum value in String, takes the value of the field itself. ) Use Enums in HibernateIn this example we will be using Enums to save a value in database using hibernate.Suppose...

Points To RememberSuppose we have two domains/ entities User and Role and we want to create a many to many relationship between them them, then we can do it like following in hibernate. Many to Many relationship between two Entities. User.java Create a User class as following package com.ekiras.domain;import java.util.ArrayList;import java.util.Collection;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.ManyToMany;import javax.persistence.Table;@Entity@Table(name = "user")public class User { @Id @GeneratedValue(strategy=GenerationType.AUTO) @Column(name="id") private Long id; @Column(name="email") private String email; @Column(name="password") private String password; @Column(name="enabled") private boolean enabled; @ManyToMany(cascade=CascadeType.ALL) private Collection<Role> roles = new ArrayList<Role>(); // GETTERS and SETTERS Role.java Create the Role class as follows package com.ekiras.domain;import java.util.ArrayList;import java.util.Collection;import...

Points To RememberThere are two ways to create hibernate many to many relational mappings in Hibernate. We will discuss both of them in detail here. First one is to use default hibernate mapping to create and manage these relations. By creating a new domain that will manage these relations for us. Suppose we want to have a simple User and Role mapping where a user can have multiple roles and a role can be assigned to multiple users. Then we can create and manage these relations in the following ways. Strategy 1 : Default Hibernate MappingsYou can use this strategy...

Points To RememberYou can define your custom error pages in web.xml. This is the best way to define custom 404 and other error pages. Configure Custom error pagesMany times we want to create custom error pages in our web applications like for a 404 error, resource not found, 500 internal server error and other errors that we see commonly. So we may want to redirect such errors to a better looking custom error page.If you want to redirect to custom error pages in a web application you can add these custom error pages in web.xml like following. web.xml <error-page> <error-code>400</error-code> <location>/error/400.html</location>...

Points To RememberYou can convert the number from decimal to any base by dividing the number by the base till the number is either 0 or less than the base it self and counting the remainders in a reverse order. Program : Convert the base of a Decimal Number import java.util.Scanner;class ConvertBase{ public static void main(String args[]){ Scanner sc = new Scanner(System.in); System.out.println("Enter the Original NUmber"); int originalNumber = sc.nextInt(); System.out.println("Enter the base for conversion"); int base = sc.nextInt(); String convertedNumber = new ConvertBase().convert(originalNumber,base); System.out.println("Original Number = "+originalNumber); System.out.println("Converted NUmber = "+convertedNumber); } public String convert(int original, int base){ String...

Concepts Examples How To Solve Allegations Suppose the average weight of a group of objects O1 is A1 and average weight of group of objects O2 is A2 and A1 2, then we can write the data in the manner as shown in the figure. (Aw−A2) : (Aw−A1) gives the ratio of O1 : O2. Allegations does not give the actual volume to be mixed but only the ratio in which volumes are to be mixed. Question 1 A shopkeeper sells two types of rice A and B. If he sold 30% of type A rice at a profit of...

Points To RememberYou may need to create an AuthenticatioFilter when you want to create a custom logic for handling the authentication filter. You may also want to create your own Authentication Provider, Entry Point, Authentication Token etc to customize the authentication process to a new level. Step 1 : Create a FilterLet us first create a class named MyAuthenticationFilter and then register it as a bean in resources.groovy. After we have created the class and registered the it as a bean, we can use this class as a filter for our custom spring security authentication.Class : MyAuthenticationFilter.groovy package com.ekirasimport org.springframework.context.ApplicationEventPublisherimport org.springframework.security.authentication.UsernamePasswordAuthenticationTokenimport...

Points To Remember Each Servlet has its own ServletConfig object. ServletConfig is defined in web.xml ServletConfig is a way of giving init parameters to a servlet during initialization.  ServletConfig is a predefined interface. ServeltConfig object is created by the container when a servlet is initialized and this object remains with the servlet throughout the life cycle of the servlet. Example : How to get ServletConfig Object in a Servlet. Lets take an example where we will add a few init params in the servlet config and get the config object from the servlet config object within the servlet. package com.ekiras;import...

Points To Remember You to need to add the Reflections jar in the class path.  You will not be able to load the packages other than the current package using Package.getPackages() since current class loader will not be able to reach them. Program : Scan all packages with a PrefixYou can use Package.getPackages() approach to find all the packages that are in the current class loader. But you will not be able to get the packages that are not in the class path of the current class loader. So you need to include the jar "Reflections" to do this for you.All the dependency to the...

Points To Remember You need to have a SSL certificate o run an application/ server on https. You can create a SSL certificate using keytool. The keystore file for Java is available in Java/jre/lib/security/cacerts. Default password of the keystore is "changeit". Create a KeystoreYou can make a SSL certificate by following the steps below. Open a Command-line or Terminal window and make sure you're in your home directory. Execute the following command in the terminal keytool -genkey -alias tomcat -keyalg RSA -validity 365 NOTE, the validity parameter allows you to specify, in the number of days, how long the certificate...

Points To Remember To make a class Singleton the class must satisfy the following points No class should be able to make the object of this class. Only one object of this class must me there that is used by all the other classes. The class must have a private constructor so that no class should be able to make object of this class. Class should make a final object of the class itself and return it whenever asked for. Class should have a static method that returns the object of this class. Demo : Create a Singleton ClassClass :...

Points To Remember The Correct Datatype for creating a Nested List will be List<Object>, because we have to store either a integer number or a list inside the list. We can not have a nested list like List<List<Integer>> because it will not be able to hold the integer values. It can only hold a list. The List we create can be nested to any level. Program : Create A nested list upto any levelHere we suppose that we get a String input of the list that we have to create. The following program accepts the list as a String and returns after converting...

Concepts Examples If a number x divides another number y completely then x is a divisor of y. If x is a prime number then x is called the prime factor of number x. e.g 1,2,3,6 are the factors of 6 and 2,3 are the prime factors of 6. If any composite number N which can be expressed as N=$a^x\cdot b^y\cdot c^z...$ax·by·cz... , where a,b,c are the prime numbers and x,y,z are the powers of a,b,c respectively and so on. then the number of factors of N =(x+1)×(y+1)×(z+1)... e.g Find the number of factors of 24 24=22×31 ∴ number of...

Points To Remember You can user MYSQL, Oracle or PostgreSQL connectors as the database. Make sure you have created a SSL certificate to run the CAS server on browser. Step 1: Adding Dependencies in pom.xmlAdd the following dependencies to the pom.xml that we created in this tutorial. These are the dependencies that are required to authenticate the user using the database. <dependency> <groupId>org.jasig.cas</groupId> <artifactId>cas-server-support-generic</artifactId> <version>${cas.version}</version> <type>jar</type> <scope>runtime</scope> </dependency> <dependency> <groupId>org.jasig.cas</groupId> <artifactId>cas-server-support-jdbc</artifactId> <version>${cas.version}</version> </dependency> <dependency> <groupId>c3p0</groupId> <artifactId>c3p0</artifactId> <version>0.9.1.2</version> </dependency> <dependency> <groupId>org.jasig.cas</groupId> <artifactId>cas-server-integration-restlet</artifactId> <version>${cas.version}</version> <type>jar</type> </dependency> So now the pom.xml will look like the following <?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd ">...

Points To Remember You should have a war file that can be deployed to the tomcat. You should have tomcat installed on your machine. Deploying a war file on Tomcat. We hope you have a installed the tomcat or have the tomcat bundle extracted on your system. In your case we just downloaded the tomcat zip and unzipped at home location. Step 1 : Change Tomcat User Name Password and Roles This is done so that you can login to the Tomcat Application Manager. All you need to do is find the file tomcat-user.xml at location path-to-tomcat/conf. Replace the following...

Concepts Examples There are three types of questions that are based on LCM with remainders. They are as follows. When the remainders are same for all the divisors In this case the required number will be the LCM × N + remainder, where N is any natural number N=1, will give smallest such number N=2, will give second smallest such number and so on When the remainders are different for different divisors but the respective difference between the divisors and the remainders remain constant. In this case the required number will be LCM × N +difference of any (divisor -...

Concepts Examples To find the last digit i.e the unit digit you need to be aware of the cyclicity of the numbers and their powers 21=2 31=3 41=4 22=4 32=9 42=16 23=8 33=27 43=64 24=16 34=81 44=256 25=32 35=243 45=1024 26=64 36=729 46=4096 27=128 37=2187   28=256 38=6561   We can see that unit's digit of 21,25,29 is 2 and so on. Therefore, after every four powers of 2, the units digit of the number starts repeating.Thus we can say that cyclicity of unit's digit of higher powers of 2 is 4. Similarily unit digit of power of 4 starts...

Concepts Examples To find the number of zeros at the end of a factorial or a product, find the highest power of 2 and 5 in the factorial or the product, number of zeros will be decided by the limiting factor. ( one who's power is smaller will be the limiting factor) Limiting factor is the one who's power is less among 2 and 5 e.g. Finding number of Zeros in 150 150 = 2 × 3 × 5 × 5, ∴ Highest power of 2 = 1 ∴ Highest power of 5 = 2 ∴ Limiting factor = 1...

Points To Remember By default, in grails all the html code and script code is escaped. You can render your html string as html in three ways, change in config, change at page level and change at field level.  Rendering HTML String in a GSP in Grails. Suppose we have a String like the following and we want it to get rendered as HTML in our gsp. By default out code will get rendered like this. Hi < br />My name is Ekansh Rastogi < br />I want this in three lines. But we wanted out output as Hi My...

Points To Remember Both the method equals() and hashCode() are the methods of Object class, hence available in all the classes. Syntax for equals() method in Object class is public boolean equals(Object obj) Syntax for hashCode() method in Object class is public int hashCode() The equals() method of Object class checks if the two references compared point to same object, returns true if they are same and false if two objects are different. We can override this functionality by our own custom way of comparing objects. If the equals() method returns true, then the hashcode() of the two object must be same....

Points To Remember A foreign key is a key that is a primary key in some another and is used to maintain a relationship with this table. Foreign key constraint failure occurs when we are trying to assign a value to a foreign key, that does not exist in the other table of which it is primary key. Solution : How to ignore Foreign key constraint failure When you need to avoid foreign key constraints, you can do SET FOREIGN_KEY_CHECKS=0; When you again need to set foreign key constraints on you can, SET FOREIGN_KEY_CHECKS=1; Note : This is not recommended...

Question : Count the number of occurrences of each word in a String Write a program to accept a string from the user and print the number of times each word of the string occurs in the input string.e.gIf the input is "Tinkle Twinkle little star" then the output should beTwinkle  - 2little        -1star         -1 Program  import java.util.HashMap;import java.util.Scanner;class CountOccurances{ public static void main(String args[]){ CountOccurances obj = new CountOccurances(); System.out.println("Enter the line of String"); String max = obj.maxOccurances(new Scanner(System.in).nextLine().split(" ")); System.out.println("Word with maximum occurances = " + max); } public String maxOccurances(String[] str){ HashMap<String,Integer> map...

This test contains 10 questions based on Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes : seconds Weakest access specifier among the following is public private default protected B private has the weakest access among all. Private members of a class can be accessed only within the same class. Which access specifier should be used with a class...

Points To Remember HashMap saves objects in form of key-value pair in form of Entry object (Map.Entry). We can use any object as a key on which hashCode() and equals() can be applied. We cannot use primitive datatypes as keys or values. We can have only one value corresponding to a key, other values will get overridden. A hashMap can contain a single null key. Initial size of a HashMap is 16 and its load factor is 0.75 after this HashMap gets rehashed. Program : Adding Objects to HashMap Below program shows how to save key-value pairs as entry objects...

This test contains 10 questions based on Fundamentals Of Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes : seconds Which of the following is not a conditional statement. while if for do while B if is the conditional statement out of these all the others are the loops. Which of the following is not a keyword in java....

Points To Remember We can use reflection to find all the fields available within a class. We can get all the declared fields in a class by getDeclaredFields(). We can search for any field in a class by using getField(). It throws NoSuchFieldException if the field does not exist in the class. Program : Get all the declared fields in a class import java.lang.reflect.Field;class SampleClass{ String s1 = "Class variable"; int a = 123;}class Test{ public static void main(String args[]){ Test obj = new Test(); try{ Class clazz = Class.forName("SampleClass"); Field feilds[] = obj.getDeclaredFields(clazz); for(Field feild : feilds){ System.out.println(feild); } }catch(Exception e){ e.printStackTrace();...

Points To Remember We can get the constructors declared in a class using Reflection API. Constructor class is present in java.lang.reflect.Constructor class. The getDeclaredConstructors() method will return an array of Constructors in a class. Program : Get all constructors declared in a class import java.lang.reflect.Constructor;class SampleClass{ String s1 = "Class variable"; int a = 123; public SampleClass(){ System.out.println("SampleClass Default Constructor"); } public SampleClass(String str){ System.out.println("SampleClass Overloaded Constructor"); } public void show(){ System.out.println("SampleClass Show Method"); } public void print(){ System.out.println("SampleClass Print Method"); }}class Test{ public static void main(String args[]){ Test obj = new Test(); try{ Class clazz = Class.forName("SampleClass"); Constructor cc[] = obj.getConstructors(clazz); for(Constructor...

Program : Find if the given number is Armstrong A number is said to be armstrong if the sum of cube of its digits is equal to the number itself.e.g.371 is an Armstrong number, since   3^3 + 7^3 + 1^3 = 371 341 is not Armstrong number, since  3^3 + 4^3 + 1^3 = 92 import java.util.Scanner;class Armstrong{ public static void main(String args[]){ Armstrong obj = new Armstrong(); System.out.println("Enter a number to check Armstrong"); Scanner sc = new Scanner(System.in); obj.isArmstrong(sc.nextInt()); } public void isArmstrong(int n){ int sum = 0,number = n; while(n!=0){ sum += Math.pow(n%10,3); n = n/10; }...

This test contains 10 questions based on Method Overloading. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes : seconds Compile time polymorphism is also known as Method Overriding Method Overloading Method Rewriting None of these B Comiple Time polymorphism means that methods with same names gets resolved at the compile time only. JVM does not have to resolve these...

Question : Find sum of digits of number that are even. Suppose we have a number 456789 and we need to find the sum of all the digits in the number that are even or divisible by 2.e.g In number  456789 sum of even digits is 4 + 6 + 8 = 18. import java.util.Scanner;class FindSum{ public static void main(String args[]){ System.out.println("Enter the number"); Scanner sc = new Scanner(System.in); FindSum object = new FindSum(); int number = sc.nextInt(); int sum = object.findSumOfDigits(number); System.out.println("Sum of digits of "+number+" = "+ sum); } public int findSumOfDigits(int num){ int sum = 0; while(num...

Points To Remember A constructor have the same name as that of a class. A constructor does not have any return type, not even void. Constructor of a class is called first, before any other method is called. Constructor of a super class is called before the base class constructor.  We can have a private constructor in a java class. A class with a private constructor can not be inherited. We cannot create object of a class with a private constructor. What happens if we have a Private Constructor in a class. Suppose if we make a private constructor of...

This test contains 10 questions based on Fundamentals Of Java. Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers. Select Test Type Timed Test UnTimed Test You Get +1 for each correct answer and -0.25 for each incorrect answer Time Left - minutes : seconds What was the original name of Java ? Oak Pok James Coffee A Java was initially named as Oak by its founders. Who is know as the father of Java ? Ken Arnold David Holmes James Gosling Peter Dibble...

Points To Remember Servlet is a java class that implements javax.servlet.Servlet interface. Servlets are initialized by the servlet containers using init() method. Servlets like any other java class can have constructors. Servlet must have a no argument constructor in case it have a non zero arguments constructor. Servlet needs an object of ServletConfig for initialization. Interfaces cannot have constructors. Can we have Constructors in a Servlet ? Yes we can, please read How a servlet is initialized by the servlet container. So this article will make clear, why we cannot use a constructor for initializing a servlet.However there is no problem...

Points To Remember HashTable have the legacy code and were introduced before HashMaps. There is nothing in a HashTable that a HashMap cannot do except multithreading. ConcurrentHashMap is a replacement for HashTable, it a synchronized HashMap. Differences : HashMap and HashTable  HashMap HashTable They implement Map Interface. It extends Dictionary(obsolete from jdk 1.7) class and implements Map interface They are a part of Collections API They are not a part of Collections API They allow a single null key and any number of null values. They do not allow null values to be added. They are not synchronized or thread-safe...

Points To Remember ClassNotFoundException is an Exception. NoClassDefFoundError is an Error. ClassNotFoundException This is a type of error when we are trying to access a class but that class is not available at the classpath or at the path specified by us. This type of error is thrown when an application tries to load in a class through its string name using: The forName method in class Class. The findSystemClass method in class ClassLoader. The loadClass method in class ClassLoader. Example : When ClassNotFoundException occurs class A{}class Test{ public static void main(String args[]){ try{ System.out.println("classA = "+Class.forName("A").getClass()); System.out.println("classB = "+Class.forName("B").getClass());...

Points To Remember Static variable are the variables at the class level. Static variables are not attached to the objects. Static variable cannot be declared inside any method of a class. Static variables are assigned the memory only once during the execution of the class. Static variables can be called directly from static context or by class reference. Definition Static variables are the class level variable that are allocated the memory only once and they cannot be declared inside any method of a class or inside a static block or static method but can be declared only  outside all methods...

Points To Remember TreeSet is ordered and sorted Set. TreeSet extends AbstractSet and implements NavigableSet. Objects are stored in ascending order based on natural ordering. You can even define your sorting rules for sorting a TreeSet using constructors with Comparable or Comparator. It is fast for Accessing/Retrieving objects but slow for Adding/Removing objects.  Constructor : TreeSet TreeSet(); // Default ConstructorTreeSet(Collection<? extends E> c); //TreeSet from Collection CTreeSet(Comparator<? super E> comp); // TreeSet with custom ordering as per ComparatorTreeSet(SortedSet<E>ss); //TreeSet that contains the elements of ss. Example : TreeSet Implementation Suppose we have a Set of Tourists from different countries and...

Points To Remember JSP stands for Java Server Pages. Jsp at compilation time is a servlet and also behaves like a servlet. Jsp serves as views in MVC architecture. Jsp can contain HTML code inside them. They are compiled everytime they are requested. What is a JSP ? JavaServer Pages (JSP) is a technology for developing dynamic web pages with dynamic data. You can write java code within a jsp along with the Html using special Jsp tags most of which start with <% and end with %>.A JavaServerPage component is a type of Java servlet that is designed to fulfill...

Points To Remember A filter is hit before the servlet or a controller is hit and before the response is sent back to the client. Filters can be used to apply some action on application level. A filter implements the javax.servlet.Filter interface and the primary filter functionality is implemented by the doFilter() method of the filter. Filters can be used to manipulate both requests from client and response from server. What is a Filter in Java Web Applications ? A filter is a useful way of performing filtering operations in java web applications bith before a request reaches the backend...

What is Spring Roo ? Spring Roo is a spring productivity tool that simply reduces the pain of a developer by doing all the configuration related stuff for a project. Spring Roo does not require any extra knowledge  expect java. Roo makes it fast and easy to build full Java applications in minutes. Why Use Spring Roo ? Following are the points why we should use Spring Roo. Higher Productivity - We can get started with the java project just in minutes and the roo follows the best practice standard methods to create the application for us Stock Standard Java...

Difference between Comparator and Comparable Comparator Comparable It is available in java.util package. It is available in java.lang package. We need to override compare() method. We need to override compareTo() method. It takes two arguments as parameters.public int compare(Object obj1,Object obj2 )  It takes only one argument as a parameter.public int compareTo(Object obj) Its primary use is where we need to write the comparing logic outside the class which has to be compared.   It is used when we need to compare the instance of an object with a given object. Comparing logic is inside the class that needs to be compared....

First things that comes in mind are A class is a blueprint from which objects are created. They are wrappers and have everything inside them e.g Functions/Methods/Variables etc. They can be public or default but not private or protected. Each Class has a name, and may belong to a package. A class can have both static and non static methods and variables. A class can not be static (however inner classes can be). Definition A class is the blueprint from which individual objects are created. A class containes A main method marked as public static void and taking an array...

Program : Reverse each word of String  Write a program that takes a string input from the user and then reverse each word of the of the line as entered by the user.Expected input   : "This is a very good blog"Expected output : "sihT si a yrev doog golb" import java.io.*;public class ReverseString{ public static void main(String args[]){ ReverseString obj = new ReverseString(); String inputString = obj.getStringFromUser(); String outputString = ""; String aux = ""; for(int itr=0;itr<inputString.length();itr++){ // reverse the words if a whitespace occurs. if(inputString.charAt(itr) == ' '){ outputString += reverseString(aux) + " "; aux = ""; }...

Different ways of creating Objects Using new operator. Using Class.forName() and newInstance(). Using Factory Methods Using Object cloning Using Object deserialization Object Creation By Different Methods public class ObjectCreation { public static void main(String args[])throws Exception{ ObjectCreation objecByNewKeyword = createObjecByNewKeyword(); ObjectCreation objecByClassForName = createObjecByClassForName(); ObjectCreation objecByCloning = (ObjectCreation)createObjecByCloning(); // object to be cloned objecByNewKeyword.show("new keyword"); objecByClassForName.show("using Class.forName and newInstance"); objecByCloning.show("cloning"); } public static ObjectCreation createObjecByNewKeyword(){ ObjectCreation obj = new ObjectCreation(); return obj; } public static ObjectCreation createObjecByClassForName() throws ClassNotFoundException, InstantiationException, IllegalAccessException{ ObjectCreation obj = (ObjectCreation)Class.forName("ObjectCreation").newInstance(); return obj; } public static ObjectCreation createObjecByCloning()throws CloneNotSupportedException{ ObjectCreation obj = new ObjectCreation(); ObjectCreation clone =...

Points To Remember In java 1.0, there were two primary collection classes HashMap and Vector. Enumeration was a class in Java 1.0 to Iterate through these collection classes.(They are not the enum types.) Iterator was introduced in Java 1.2 Difference between Enumeration and Iterator. Enumeration Iterator It was introduces in Java v1.0 It was introduced in java v1.2 Enumeration does not have remove() method Iterator has remove() method Enumeration provides a read only iteration over collection Iterator provides iteration over collections along with manipulation of objects like adding and removing from object. Enumeration is less safe and secure Iterator is...

Points To Remember HashMap implements the Map Interface. It works on the principles of hashing.  It stores and retrieves data in a key value pair. HashMap can have only one key as a null element. HashMap stores both key and value in form of Entry object Map.Entry.  Initial capacity of HashMap is 16. (Since jdk 1.7 we can have HashMap with initial capacity as 0). Default load Factor of a HashMap is 0.75, after this a HashMap gets rehashed.  Q1 : How does HashMap work internally ?  We add data to the HashMap in key-value pair, by method put(key, value). When we...

When a base class extends a super class and both the base class and the super class have a method with same name, same types of parameters and same number of parameters, then the two methods are said to be overriden. Points To Remember Overriding of methods is always done in a base class or in other words, we always override a parent class method. The access specifier of the overriden method can not be less than the parent class method's access specifier e.g if a parent class method is marked as protected, you can override it with access specifiers...

We can have multiple methods with the same name as long as their parameter types or number of parameters differ. These methods are called overloaded methods. This is also referred as Static Polymorphism. Points To Remember Overloading of methods is always done in the same class. The access specifier of the overloaded method may or may not be same  to the other overloaded methods. Name of the overloaded methods should be same. The overloaded methods may have different return types. Overloaded methods should have at least one of the following Different argument types Different number of arguments They provide Static...

Points to remember We can have only one entry point per class in Java. Thus we can have only one "public static void main(String args[])". Any other method with a different name or type or arguments will not be treated as a main method(). Yes, we can have multiple main methods in a java class. Surprised ?? Method Overloading, by using this you can have as many main() methods as you want as long as their types or arguments are different. However these are not actually the main() methods, these are just overridden methods and may act as any other...

Points To Remeber MIME stands for Multi-purpose Internet Mail Extensions. MIME is an extension of the original Internet e-mail protocol that lets people use the protocol to exchange different kinds of data files on the Internet: audio, video, images, application programs MIME types were originally used to send different file types through email services over SMT SMTP(Simple Mail Transfer Protocal) protocal.  MIME types form a standard way of classifying file types on the Internet e.g. using the "Content-type" header value defined in a HTTP response, the browser can open the file with the proper extension/plugin.   Internet programs such as Web...

Syntax : SHOW CREATE TABLE tablename When To Use ? You already have a table in the database and you want to view how this table was created. You want to check all the datatypes, default value, nullability of the columns. You want to see all the constraints and keys that are applicable to this table. This command can be used to recreate the table as it is with all constraints and keys set.  Example Suppose we have two tables Institute and User  and we want to check the schema of the tables or in simple terms how these tables...

There are 4 types of Generation Strategies that can be used to generate Id in hibernate. AUTO  e.g. strategy = GenerationType.AUTO IDENTITY e.g. strategy = GenerationType.IDENTITY SEQUENCE e.g. strategy = GenerationType.SEQUENCE TABLE e.g. strategy = GenerationType.TABLE strategy = GenerationType.AUTO This is the default Generation Strategy that is used by the hibernate. This strategy allows hibernate to decide what strategy to be used to generate the unique key for the table. Strategies used by hibernate can be different for different types of databases used. strategy = GenerationType.IDENTITY In this Generation Strategy the hibernate is going to use an identity column. Identity column is a...

First things that comes in mind are They are real things They occupy some space in memory They have a state and some characteristics Definition Java Objects are the real world entities that can have a state and some behavior. They are created from a blueprint i.e. classes. Example If we say that Person is a class, then person is a blue print of every human in this world and we are all the objects of this class Person.Since each object has some state and some characteristics, thus we may be similar or different from each other ion the basis of...