Spring核心技术之Bean的作用域 Mr

在spring中bean的作用域是spring容器用来返回调用者实例类型的

在spring中有5中类型的作用域：

先来比较一下singeton 和 prototype:

package springapp.test;

  
/**     
 * @author zhangxuegang       
 * @version 1.0     
 * @created 2012-10-16 下午11:09:38    
 */

public class CustomerService 
{
	String message;
 
	public String getMessage() {
		return message;
	}
 
	public void setMessage(String message) {
		this.message = message;
	}
}

Singeton的例子当不指定作用域的时候spring默认的为singeton

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
	xmlns:tx="http://www.springframework.org/schema/tx"
	xsi:schemaLocation="http://www.springframework.org/schema/beans 
           http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
           http://www.springframework.org/schema/aop 
           http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
           http://www.springframework.org/schema/tx 
           http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">
	<bean id="testSpring" class="springapp.test.TestSpring">
	</bean>
	<bean id="exampleBean" class="springapp.test.ExampleBean"
		factory-method="createInstance">
		<constructor-arg type="int" value="7500000" />
		<constructor-arg type="java.lang.String" value="42" />
	</bean>
	<bean id="customerService" class="springapp.test.CustomerService" />
</beans>

　　

测试：

package springapp.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

  
/**     
 *      
 * 测试作用域为singeton    
 * @author zhangxuegang       
 * @version 1.0     
 * @created 2012-10-16 下午11:12:55    
 */

public class TestSingeton {
    public static void main( String[] args )
    {
        ApplicationContext ctx = new ClassPathXmlApplicationContext(  
        "file:F:/springProject/springapp/war/WEB-INF/applicationTest.xml");
 
    	CustomerService custA = (CustomerService)ctx.getBean("customerService");
    	custA.setMessage("Message by custA");
    	System.out.println("Message : " + custA.getMessage());
 
    	//retrieve it again
    	CustomerService custB = (CustomerService)ctx.getBean("customerService");
    	System.out.println("Message : " + custB.getMessage());
    }
}

　　

运行结果：

Message : Message by custA
Message : Message by custA

我们可以看到当作用为singleton时，无论你调用多少次getbean方法，

返回的都是一样的实例，因为在spring容器中只产生了一个单例的实例

 

当你每次调用customerServicebean的时候都想返回一个新的实例，那么你需要用prototype去替换它：

<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>

　　

测试结果：

Message : Message by custA
Message : null

基于注解的bean作用域：

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;
	}
}

　

启动组件的自动扫描：

<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>