spring单例和多例详解。如何在单例中调用多例对象

spring生成对象默认是单例的。通过scope属性可以更改为多例。

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<bean id="user" class="modle.User" scope="prototype">

</bean>

现在又这么一种情况.

User类调用一个service， 这个service又调用一个tool。

有时我们希望User是多例的，service是单例的，而tool又是多例的。

很自然地想法是配置文件这些写

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<bean id="user" class="modle.User" scope="prototype">

<property name="service" ref="userservice"></property>

</bean>

<bean id="userservice" class="service.userService" >

<property name="tool" ref="tool"></property>

</bean>

<bean id="tool" class="service.ToolImpl" scope="prototype"></bean>

但是这种写法是错误的！ 不能使用spring的自动注入！

由于service是单例的，所以这种方法的结果是：User多例，service和tool都是单例。（为什么？）

官网文档：

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4.5.3 Singleton beans with prototype-bean dependencies

When you use singleton-scoped beans with dependencies on prototype beans, be aware that dependencies are resolved at instantiation time. Thus if you dependency-inject a prototype-scoped bean into a singleton-scoped bean, a new prototype bean is instantiated and then dependency-injected into the singleton bean. The prototype instance is the sole instance that is ever supplied to the singleton-scoped bean.

However, suppose you want the singleton-scoped bean to acquire a new instance of the prototype-scoped bean repeatedly at runtime. You cannot dependency-inject a prototype-scoped bean into your singleton bean, because that injection occurs only once, when the Spring container is instantiating the singleton bean and resolving and injecting its dependencies. If you need a new instance of a prototype bean at runtime more than once, see Section 4.4.6, “Method injection”

正确的写法是，是每次调用tool时都生成一个新的tool对象。但是我们又不能手动new一个，要借助BeanFactory

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public class User {

private userService service;

private int age;

private Date date;

private String name;

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public Date getDate() {

return date;

}

public void setDate(Date date) {

this.date = date;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public userService getService() {

return service;

}

public void setService(userService service) {

this.service = service;

}

}

UserService 通过实现 BeanFactoryAware 接口来获得factory

由于不使用spring的自动注入，set方法要去掉！

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public class userService implements BeanFactoryAware{

private Tool tool;

private BeanFactory factory;

public void service(){

this.tool = (Tool)factory.getBean("tool");

System.out.println(this+":service");

tool.work();

}

public Tool getTool() {

return tool;

}

// public void setTool(Tool tool) {

//

// this.tool = (Tool)factory.getBean("tool");

// }

public void setBeanFactory(BeanFactory f) throws BeansException {

factory = f;

}

}

配置文件，不能再使用注入。因此要把tool对象的注入去掉！

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<bean id="user" class="modle.User" scope="prototype">

<property name="service" ref="userservice"></property>

</bean>

<bean id="userservice" class="service.userService" >

</bean>

<bean id="tool" class="service.ToolImpl" scope="prototype"></bean>

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public interface Tool {

public void work();

}

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public class ToolImpl implements Tool{

public void work() {

System.out.println(this+":Tool Work");

}

}

测试类：

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public class Test {

public static void main(String[] args) {

ClassPathResource res = new ClassPathResource("applicationContext.xml");

XmlBeanFactory factory = new XmlBeanFactory(res);

User user = (User)factory.getBean("user");

User user2 = (User)factory.getBean("user");

System.out.println(user);

user.getService().service();

System.out.println();

System.out.println(user2);

user2.getService().service();

}

}

Output:

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modle.User@42552c

service.userService@19e15c:service

service.ToolImpl@11a75a2:Tool Work

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modle.User@210b5b

service.userService@19e15c:service

service.ToolImpl@170888e:Tool Work