spring单例和多例详解的实验,以及如何使用多例模式
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原文:http://www.tuicool.com/articles/RzIvAj
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 dependenciesWhen 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@42552cservice.userService@19e15c:serviceservice.ToolImpl@11a75a2:Tool Work
modle.User@210b5bservice.userService@19e15c:serviceservice.ToolImpl@170888e:Tool Work
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