CDI组件技术（三）—— 拦截器，修饰器

@Interceptor

拦截器
功能：断开逻辑插入功能，比如Logger
定义一个拦截器LoggedInterceptor.java

@Logged 
@Interceptor
public class LoggedInterceptor implements Serializable {

    public LoggedInterceptor(){}
    
    // 拦截之后具体实现
    @AroundInvoke
    public Object  logMethod(InvocationContext ctx) throws Exception {
        System.out.println("Entering method:" + ctx.getMethod().getName()
        + " in class: " + ctx.getMethod().getDeclaringClass().getName());
        return ctx.proceed();
    }
}

调用拦截器

 @Logged
 public void checkin(){
     System.out.println("checkin room......");
 }

当然拦截器需要在beans.xml上激活

<beans xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
      http://java.sun.com/xml/ns/javaee
      http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
    <interceptors>
        <class>cn.edu.sdut.r314.AuditInterceptor</class>
        <class>cn.edu.sdut.r314.LoggedInterceptor</class>
    </interceptors>
</beans>

当然拦截器也可以修饰一整个组件，这样只要调用这个组件的时候就会执行拦截器的内容

@Named
@Audit
public class RoomController {

    /**
     * 订房
     * @return
     */
    public void checkin(){
        System.out.println("checkin room......");
    }

    /**
     * 退房
     * @return
     */
    public void checkout(){
        System.out.println("checkout room......");
    }
}

@Decorator

功能：修饰器，横向
注册一个修饰器类PaintedDecorator.java

@Decorator
public class PaintedDecorator implements Room {

  @Inject
  @Delegate
  Room roomToBeDecorated; //注册被修饰的房子，这里是BlankRoom

  public String showRoom() {
    doPainting();
    return roomToBeDecorated.showRoom() + "刷墙漆";
  }

  // 刷墙漆
  private void doPainting() {
       System.out.print("刷墙漆");
  }
}
-------------------------------------------------------------------------------------------------------------------
@Decorator
public class FlooredDecorator implements Room {

  @Inject
  @Delegate
  Room roomToBeDecorated;  //注册被修饰的房子，这里是BlankRoom

  public String showRoom() {
    doFlooring();
    return roomToBeDecorated.showRoom() + "铺地板";
  }
  // 铺地板
  private void doFlooring() {
      System.out.print("装饰地板");
  }
}

注册两个被修饰类BlankRoom.java,修饰的基础

public class BlankRoom implements Room {

  public String showRoom() {
    return "毛胚房";
  }
}

激活修饰器，执行顺序由下至上

 <!-- 改变decorators类的顺序，观察一下浏览器的不同输出 -->
    <decorators>
        <class>cn.edu.sdut.softlab.FlooredDecorator</class>
        <class>cn.edu.sdut.softlab.PaintedDecorator</class>
    </decorators>

具体实现

@Named("room")
public class RoomController {

  @Inject
  Room room;

  public String showRoom() {
    return room.showRoom();
  }
}

输出

毛胚房刷墙漆铺地板

示例代码：
https://github.com/liuqinyi/weld-tutorial
https://github.com/liuqinyi/quickstart.git