Spring - bean scopes example

In Spring, bean scope is used to decide which type of bean instance should be return from Spring container back to the caller.

5 types of bean scopes supported :

1. singleton – Return a single bean instance per Spring IoC container
2. prototype – Return a new bean instance each time when requested
3. request – Return a single bean instance per HTTP request. *
4. session – Return a single bean instance per HTTP session. *
5. globalSession – Return a single bean instance per global HTTP session. *

In most cases, you may only deal with the Spring’s core scope – singleton and prototype, and the default scope is singleton.

Singleton vs Prototype

Here’s an example to show you what’s the different between bean scope : singleton andprototype.

package com.mkyong.customer.services;

publicclassCustomerService

{

        String message;

        public String getMessage(){

               return message;

        }

        publicvoidsetMessage(String message){

               this.message = message;

        }

}

            

1. Singleton example

If no bean scope is specified in bean configuration file, default to singleton.

<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-2.5.xsd">

<bean id="customerService" 

            class="com.mkyong.customer.services.CustomerService" />

</beans>

Run it

package com.mkyong.common;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.mkyong.customer.services.CustomerService;

publicclassApp

{

publicstaticvoidmain( String[] args )

{

        ApplicationContext context =

        newClassPathXmlApplicationContext(newString[]{"Spring-Customer.xml"});

        CustomerService custA =(CustomerService)context.getBean("customerService");

        custA.setMessage("Message by custA");

        System.out.println("Message : "+ custA.getMessage());

        //retrieve it again

        CustomerService custB =(CustomerService)context.getBean("customerService");

        System.out.println("Message : "+ custB.getMessage());

}

}

Output

Message : Message by custA

Message : Message by custA

Since the bean ‘customerService’ is in singleton scope, the second retrieval by ‘custB’ will display the message set by ‘custA’ also, even it’s retrieve by a new getBean() method. In singleton, only a single instance per Spring IoC container, no matter how many time you retrieve it with getBean(), it will always return the same instance.

2. Prototype example

If you want a new ‘customerService’ bean instance, every time you call it, use prototype instead.

<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-2.5.xsd">

<bean id="customerService" class="com.mkyong.customer.services.CustomerService" 

         scope="prototype"/>

</beans>

Run it again

Message : Message by custA

Message : null

In prototype scope, you will have a new instance for each getBean() method called.

Request scope vs Prototype scope

Prototype creates a brand new instance everytime you call getBean on the ApplicationContext. Whereas for Request, only one instance is created for an HttpRequest. So in a single HttpRequest, I can call getBean twice on Application and there will ever be one bean instantiated, whereas that same bean scoped to Prototype in that same single HttpRequest would get 2 different instances. 

HttpRequest scope 
Mark mark1 = context.getBean("mark"); 
Mark mark2 = context.getBean("mark"); 
mark1 == mark2; //This will return true 

Prototype scope 

Mark mark1 = context.getBean("mark"); 
Mark mark2 = context.getBean("mark"); 
mark1 == mark2; //This will return false