Spring JSR-250 Annotations

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Spring also JSR-250 based annotations which include @PostConstruct, @PreDestroy and @Resource annotations. Though these annotations are not really required because you already have other alternates but still let me give a brief idea about them.

@PostConstruct and @PreDestroy Annotations:

To define setup and teardown for a bean, we simply declare the <bean> with init-method and/or destroy-method parameters. The init-method attribute specifies a method that is to be called on the bean immediately upon instantiation. Similarly, destroy-method specifies a method that is called just before a bean is removed from the container.

You can use @PostConstruct annotation as an alternate of initialization callback and @PreDestroy annotation as an alternate of destruction callback as explained in the below example.

Example

Let us have working Eclipse IDE in place and follow the following steps to create a Spring application:

StepDescription
1Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project.
2Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3Create Java classes HelloWorld and MainApp under the com.tutorialspoint package.
4Create Beans configuration file Beans.xml under the src folder.
5The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

Here is the content of HelloWorld.java file:

package com.tutorialspoint;
import javax.annotation.*;

public class HelloWorld {
   private String message;

   public void setMessage(String message){
      this.message  = message;
   }

   public String getMessage(){
      System.out.println("Your Message : " + message);
      return message;
   }
   @PostConstruct
   public void init(){
      System.out.println("Bean is going through init.");
   }
   @PreDestroy
   public void destroy(){
      System.out.println("Bean will destroy now.");
   }
}

Following is the content of the MainApp.java file. Here you need to register a shutdown hook registerShutdownHook() method that is declared on the AbstractApplicationContext class. This will ensures a graceful shutdown and calls the relevant destroy methods.

package com.tutorialspoint;

import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {

      AbstractApplicationContext context = 
                          new ClassPathXmlApplicationContext("Beans.xml");

      HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
      obj.getMessage();
      context.registerShutdownHook();
   }
}

Following is the configuration file Beans.xml required for init and destroy methods:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd">

   <context:annotation-config/>

   <bean id="helloWorld" 
       class="com.tutorialspoint.HelloWorld"
       init-method="init" destroy-method="destroy">
       <property name="message" value="Hello World!"/>
   </bean>

</beans>

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message:

Bean is going through init.
Your Message : Hello World!
Bean will destroy now.

@Resource Annotation:

You can use @Resource annotation on fields or setter methods and it works the same as in Java EE 5. The @Resource annotation takes a 'name' attribute which will be interpreted as the bean name to be injected. You can say, it follows by-name autowiring semantics as demonstrated in the below example:

package com.tutorialspoint;

import javax.annotation.Resource;

public class TextEditor {
   private SpellChecker spellChecker;

   @Resource(name= "spellChecker")
   public void setSpellChecker( SpellChecker spellChecker ){
      this.spellChecker = spellChecker;
   }
   public SpellChecker getSpellChecker(){
      return spellChecker;
   }
   public void spellCheck(){
      spellChecker.checkSpelling();
   }
}

If no 'name' is specified explicitly, the default name is derived from the field name or setter method. In case of a field, it takes the field name; in case of a setter method, it takes the bean property name.



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