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 usoft;
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;
package usoft;
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.
<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.
3. Bean scopes annotation
You can also use annotation to define your bean scope.
package usoft;
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>