Spring中Bean的作用域

在Spring中，bean对象可以有多种作用域

 

以下测试中所需的文件：

PersonService接口 

package org.spring.service;

public interface PersonService {
	public void showMessage();
}

PersonService的实现类PersonServiceBean

package org.spring.service.impl;

import org.spring.service.PersonService;

public class PersonServiceBean implements PersonService {   
	public PersonServiceBean() {
		System.out.println("实例化...");
	}
    public void showMessage() {   
    	System.out.println("Hello Spring World!");
    }   
} 

  

1、singletion 默认的，每个IOC容器只创建一个Bean实例

 配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<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="personServiceBean" class="org.spring.service.impl.PersonServiceBean"
		scope="singleton" />

</beans>  

 

测试类： 

package org.spring.junit;

import org.junit.Test;
import org.spring.service.PersonService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringTest {
	@Test
	public void test() {
		ApplicationContext ctx = new ClassPathXmlApplicationContext(
				"spring.xml");

		PersonService personService1 = (PersonService) ctx
				.getBean("personServiceBean");

		PersonService personService2 = (PersonService) ctx
				.getBean("personServiceBean");

		System.out.println(personService1 == personService2);

	}
}

 

控制台打印结果为实例化...与true，说明是同一个bean

 

默认情况下会在容器启动时初始化bean，但我们可以指定Bean节点的lazy-init=“true”来延迟初始化bean，这时候，只有第一次获取bean会才初始化bean。如：

<?xml version="1.0" encoding="UTF-8"?>
<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="personServiceBean" class="org.spring.service.impl.PersonServiceBean"
		scope="singleton" lazy-init="true" />

</beans>  

 

测试类

package org.spring.junit;

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

public class SpringTest {
	@Test
	public void test() {
		ApplicationContext ctx = new ClassPathXmlApplicationContext(
				"spring.xml");

	}
}

 

此时控制台什么都没有打印，测试文件修改如下之后

package org.spring.junit;

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

public class SpringTest {
	@Test
	public void test() {
		ApplicationContext ctx = new ClassPathXmlApplicationContext(
				"spring.xml");

		ctx.getBean("personServiceBean");

	}
}

 

控制台打印出了实例化...字样，说明只有在获取bean的时候才会初始化bean，也称延迟加载

 

如果想对所有bean都应用延迟初始化，可以在根节点beans设置default-lazy-init=“true“，如下：

<?xml version="1.0" encoding="UTF-8"?>
<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"
	default-lazy-init="true">

	<bean id="personServiceBean" class="org.spring.service.impl.PersonServiceBean"
		scope="singleton" />

</beans>  

 

一般情况下，我们希望在容器启动的时候就初始化配置文件中的bean，所以一般不配置成延迟加载

 

2、prototype每次从容器获取bean都是新的对象

此时配置文件如下

<?xml version="1.0" encoding="UTF-8"?>
<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="personServiceBean" class="org.spring.service.impl.PersonServiceBean"
		scope="prototype" />

</beans>  

 

测试类

package org.spring.junit;

import org.junit.Test;
import org.spring.service.PersonService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringTest {
	@Test
	public void test() {
		ApplicationContext ctx = new ClassPathXmlApplicationContext(
				"spring.xml");

		PersonService personService1 = (PersonService) ctx
				.getBean("personServiceBean");
		
		PersonService personService2 = (PersonService) ctx
				.getBean("personServiceBean");
		
		System.out.println(personService1 == personService2);

	}
}

 

控制台打印结果为

实例化...
实例化...
false

 

可以看到打印出两个实例化...，说明bean被实例化了两次，从容器获取的bean是新的对象

 

3、request每次http请求创建一个实例

 

4、session每次会话创建一个实例

 

5、globalsession每个全局Http请求创建一个实例