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