spring单例和多例详解。如何在单例中调用多例对象



         原文  http://blog.csdn.net/gaotong2055/article/details/8245036

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