spring作用域(Spring Bean Scopes Example)

http://docs.spring.io/spring/docs/2.0.x/reference/beans.html#beans-factory-scopes

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.

<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 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 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> 来自:http://www.mkyong.com/spring/spring-bean-scopes-examples/
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