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 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