Spring bean destroy-method , singleton and prototype scopes

Question

I am new to the spring framework, started with some tutorials to learn it.

I have following files,

# MainProgram.java

package test.spring; import org.springframework.context.support.AbstractApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext;  public class MainProgram {         public static void main(String[] args) {               AbstractApplicationContext context =                                new ClassPathXmlApplicationContext("Bean.xml");                    HelloSpring obj = (HelloSpring) context.getBean("helloSpring");               obj.setMessage("My message");               obj.getMessage();               context.registerShutdownHook();          }  } 

# HelloSpring.java

package test.spring;  public class HelloSpring   {      private String message;       public void setMessage(String message){       this.message  = message;       System.out.println("Inside setMessage");    }     public void getMessage(){       System.out.println("Your Message : " + this.message);    }     public void xmlInit() {     System.out.println("xml configured  initialize");    }       public void xmlDestroy() {     System.out.println("xml configured destroy");     }    } 

# Bean.xml

    <?xml version="1.0" encoding="UTF-8"?>     <beans xmlns="http://www.springframework.org/schema/beans"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://www.springframework.org/schema/beans         http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">       <bean id="helloSpring" class="test.spring.HelloSpring"            scope="prototype" init-method="xmlInit" destroy-method="xmlDestroy">       </bean>      </beans> 

When I take scope="singleton" my output is :

 xml configured  initialize  Inside setMessage  Your Message : My message  xml configured destroy 

When I take scope="prototype" my output is :

 xml configured  initialize  Inside setMessage  Your Message : My message 

xmlDestroy() method is called with singleton scope bean but not with prototype kindly help me for the following ,

Is this correct? if so, what would be possible reasons?

Also I have some queries like,

what is difference or relation between ApplicationContext , AbstractApplicationContext and ClassPathXmlApplicationContext

Answer 1

xmlDestroy() method is called with singleton scope bean but not with prototype because

Spring does not manage the complete lifecycle of a prototype bean: the container instantiates, configures, decorates and otherwise assembles a prototype object, hands it to the client and then has no further knowledge of that prototype instance. For releasing resources try to implement a custom bean post processor.

Unlike singleton beans where the spring container manages the complete life-cycle

You can have a look at this basic tutorial for differences between different contexts

Refer documentation

Answer 2

A singleton bean means that there is exactly one instance of that bean in the application context. That means if you do something like this:

HelloSpring obj = (HelloSpring) context.getBean("helloSpring");     obj.setMessage("My message");     System.out.printIn(obj.getMessage());     HelloSpring anotherObj = (HelloSpring) context.getBean("helloSpring");     System.out.printIn(anotherObj.getMessage()); 

You will see "My message" in the console output twice.

For prototype beans everytime you try to get one of those from the application context you will get a new instance so if you run the above code again the second console output will be "null".

As there is no need for the container to call a destroy method for a prototype bean, it does not and the behavior is correct.

The difference between the said classes are that they are an interface, an abstract class and a concrete class respectively, to understand better about that concepts I suggest reading the official oracle documentation for java in here Oracle Java Tutorials.