【spring源码之Lookup注解的简单应用】

1. 代码示例1： 如果是抽象类那么抽象类上得是Lookup注解，此时才能将resource注册成一个

   Appconfig.java

@Configuration
@ComponentScan(basePackages= "com.luban")
public class AppConfig {


}

UserService.java

@Component
public abstract class UserService{
	public void test(){
		System.out.println("test");
	}
}

Test.java

public class Test {
 public static 	void main(String[] args) {	AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
 	UserService userService = (UserService) applicationContext.getBean("userService");
 	userService.test();
}    
/* 打印Connected to the target VM, address: '127.0.0.1:53158', transport: 'socket'
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'userService' available
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:833)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1334)
 at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:306)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:204)
 at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1153) 
*/

如果此时修改UserService类时：

@Component
public abstract class UserService{
   public void test(){
      System.out.println("test");
   }
   
   @Lookup
   public void a(){
      System.out.println("a");
   }
}
// 成功输出test

2.代码示例

UserServie.java

@Component
public  class UserService{
	@Autowired
	private OrderService orderService;

	public void test(){
		System.out.println(orderService);
	}

}

OrderService.java

@Component
@Scope("prototype")
public class OrderService {
}

Tset.java

public class Test {
	public static 	void main(String[] args) {	AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
		UserService userService = (UserService) applicationContext.getBean("userService");
		userService.test();
}    
/* 打印
com.luban.service.OrderService@3bb9a3ff
com.luban.service.OrderService@3bb9a3ff
com.luban.service.OrderService@3bb9a3ff
*/

有没有很奇怪这边打印三次的OrderService 是同一个，我们不再在OrderService类上面加了@@Scope("prototype")

其实这个问题很简单，只要我们想一下就能知道了，因为UserService 在spring容器中的对象是非懒加载的单例bean，所以对应的OrderService属性注入只能够注入一次，这一点而都不奇怪。

修改代码

UserService.java

@Component
public  class UserService{
	@Autowired
	private OrderService orderService;


	public void test(){
		System.out.println(a());
	}

	@Lookup("orderService")
	public OrderService a(){
		return null;
	}

}

OrderService.java

@Component
@Scope("prototype")
public  class OrderService {
}

Test.java

public class Test {
	public static 	void main(String[] args) {	AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
		UserService userService = (UserService) applicationContext.getBean("userService");
		userService.test();
}    
/* 打印
com.luban.service.OrderService@123ef382
com.luban.service.OrderService@dbf57b3
com.luban.service.OrderService@384ad17b
*/