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 :
- singleton – Return a single bean instance per Spring IoC container
- prototype – Return a new bean instance each time when requested
- request – Return a single bean instance per HTTP request. *
- session – Return a single bean instance per HTTP session. *
- 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.

P.S * means only valid in the context of a web-aware Spring ApplicationContext

Singleton vs Prototype

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

package com.mkyong.customer.services;public class CustomerService {    String message;    public String getMessage() {        return message;    }    public void setMessage(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;public class App {    public static void main( String[] args )    {        ApplicationContext context =          new ClassPathXmlApplicationContext(new String[] {"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 custAMessage : 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 custAMessage : null

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

3. Bean scopes annotation

You can also use annotation to define your bean scope.

package com.mkyong.customer.services;import org.springframework.context.annotation.Scope;import org.springframework.stereotype.Service;@Service@Scope("prototype")public class CustomerService {    String message;    public String getMessage() {        return message;    }    public void setMessage(String message) {        this.message = message;    }}

Enable auto component scanning

<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-2.5.xsd    http://www.springframework.org/schema/context    http://www.springframework.org/schema/context/spring-context-2.5.xsd">       <context:component-scan base-package="com.mkyong.customer" /></beans>