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.

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.

Run it again

Message : Message by custA
Message : 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; 
    }
}

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