职责链模式ChainOfResponsibility

原创转载请注明出处：https://www.cnblogs.com/agilestyle/p/11407114.html 

1.定义

使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

2.结构图

Handler：定义职责的接口，通常在这里定义处理请求的方法，可以在这里实现后继链。
ConcreteHandler：实现职责的类，在这个类中，实现对在它职责范围内请求的处理，如果处理，就继续转发请求给后继者。
Client：职责链的客户端，向链上的具体处理对象提交请求，让职责链负责处理。

3.本质

职责链模式的本质：分离职责，动态组合。

4.Code Demo

Handler.java

 package org.fool.dp.cor;

 public abstract class Handler {
     protected Handler successor;

     public void setSuccessor(Handler successor) {
         this.successor = successor;
     }

     public abstract void handleRequest();
 }

ConcreteHandler1.java

 package org.fool.dp.cor;

 public class ConcreteHandler1 extends Handler {
     @Override
     public void handleRequest() {
         boolean someCondition = false;

         if (someCondition) {
             System.out.println("ConcreteHandler1 invoked...");
         } else {
             if (successor != null) {
                 successor.handleRequest();
             }
         }
     }
 }

ConcreteHandler2.java

 package org.fool.dp.cor;

 public class ConcreteHandler2 extends Handler {
     @Override
     public void handleRequest() {
         boolean someCondition = false;

         if (someCondition) {
             System.out.println("ConcreteHandler2 invoked...");
         } else {
             if (successor != null) {
                 successor.handleRequest();
             }
         }
     }
 }

ConcreteHandler3.java

 package org.fool.dp.cor;

 public class ConcreteHandler3 extends Handler {
     @Override
     public void handleRequest() {
         boolean someCondition = true;

         if (someCondition) {
             System.out.println("ConcreteHandler3 invoked...");
         } else {
             if (successor != null) {
                 successor.handleRequest();
             }
         }
     }
 }

Client.java

 package org.fool.dp.cor;

 public class Client {
     public static void main(String[] args) {
         Handler handler1 = new ConcreteHandler1();
         Handler handler2 = new ConcreteHandler2();
         Handler handler3 = new ConcreteHandler3();

         handler1.setSuccessor(handler2);
         handler2.setSuccessor(handler3);

         handler1.handleRequest();
     }
 }