Spring Bean Scopes Example

Posted on March 26, 2010 ,     Last modified : January 6, 2012

By mkyong

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.

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.

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

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 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.

 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">