spring单例和多例详解。如何在单例中调用多例对象

刺骨的言语ヽ痛彻心扉 2022-08-07 00:22 128阅读 0赞

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*原文*  [ http://blog.csdn.net/gaotong2055/article/details/8245036][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。

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

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！

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

[http_blog.csdn.net_gaotong2055_article_details_8245036]: http://blog.csdn.net/gaotong2055/article/details/8245036?utm_source=tuicool