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。

<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

<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：

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

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！

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！

<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>

public interface Tool {
public void work();
}

public class ToolImpl implements Tool{

public void work() {
System.out.println(this+":Tool Work");
}

}

测试类：

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:

modle.User@42552c
service.userService@19e15c:service
service.ToolImpl@11a75a2:Tool Work

modle.User@210b5b
service.userService@19e15c:service
service.ToolImpl@170888e:Tool Work