5.0 Scope and Life-Cycle of a BEAN

Scope of a BEAN

1.  life cycle of a bean
2.  How long does the bean live
3.  How many instances are create
4.  How is the bean shared

<bean id="anotherSwap" 
                   class="com.spring.demo.AnotherLogic">
</bean>

here the by-default scope is Singleton

• Spring container creates only one instance
• It is cached in memory
• All request for the bean will return a shared reference to the same bean

Example - obj1 and obj2 pointing to the same bean

Swap obj1=(Swap) context.getBean("Dontswap", Swap.class);

DontSwap obj2=(DontSwap) context.getBean("Dontswap",DontSwap.class);

 

we can explicitly specify bean scope

<bean id="anotherSwap" 
                   class="com.spring.demo.AnotherLogic
                   scope="singleton">
</bean>

LIFE CYCLE OF A BEAN

---------------------------------------------------------------------------------

MyAppLifeCycleTest.java

---------------------------------------------------------------------------------

package com.spring.demo;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyAppLifeCycleTest {

public static void main(String[] args) {
ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext("lifecycle-applicationContext.xml");
Swap obj=(Swap) context.getBean("Swapme",Swap.class);
obj.doSwap(1, 2);
context.close();

}

}

---------------------------------------------------------------------------------

lifecycle-applicationContext.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" 

    xmlns:context="http://www.springframework.org/schema/context"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context.xsd">

<bean id="anotherSwap" class="com.spring.demo.AnotherLogic">

</bean>

<bean id="Swapme" 

class="com.spring.demo.SecondMethodSwap"

init-method="doStuff"

destroy-method="doMoreStuff">

<!-- Constructor injection -->

<constructor-arg ref="anotherSwap" />

</bean>

</beans>

---------------------------------------------------------------------------------

SecondMethodSwap.java

---------------------------------------------------------------------------------

package com.spring.demo;

public class SecondMethodSwap implements Swap{

private Logic logic;

public SecondMethodSwap(Logic thelogic){

logic=thelogic;

}

public void doSwap(int a, int b) {

a=a+b;

b=a-b;

a=a-b;

System.out.println("Swap using 2 variable : a = "+a+" and b= "+b);

}

public void anotherLogic(int a, int b) {

logic.anotherLogic(a,b);

}

public void doStuff(){

System.out.println("SecondMethodSwap : inside doStuff");

}

public void doMoreStuff(){

System.out.println("SecondMethodSwap : inside doMoreStuff");

}

}

---------------------------------------------------------------------------------

OUTPUT

---------------------------------------------------------------------------------

Feb 25, 2018 4:27:44 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@41975e01: startup date [Sun Feb 25 16:27:44 IST 2018]; root of context hierarchy

Feb 25, 2018 4:27:45 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [lifecycle-applicationContext.xml]

SecondMethodSwap : inside doStuff

Swap using 2 variable : a = 2 and b= 1

Feb 25, 2018 4:27:45 PM org.springframework.context.support.AbstractApplicationContext doClose

INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@41975e01: startup date [Sun Feb 25 16:27:44 IST 2018]; root of context hierarchy

SecondMethodSwap : inside doMoreStuff