目的

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，并沿着这条链发送该请求，直到有一个对象处理它位置。

类图

Handler: 定义处理请求的接口，并且实现后继链（successor）
责任链类图.png

实现

  1. public abstract class Handler{
  2.     protected Handler successor;
  4.     public Handler(Handler successor){
  5.         this.successor = successor;
  6.     }
  8.     protected abstract void handleRequest(Request request);
  9. }
  12. public class ConcreteHandler1 extends Handler{
  13.     public ConcreteHandler1(Handler successor){
  14.         super(successor);
  15.     }
  17.     @Override
  18.     protected void handleRequest(Request request){
  19.         if(request.getType() = RequestType.TYPE1){
  20.             System.out.println(request.getName() + " is handle by ConcreteHandler1");
  21.             return;
  22.         }
  23.         if(successor != null){
  24.             successor.handleRequest(request);
  25.         }
  26.     }
  27. }
  30. public class ConcreteHandler2 extends Handler{
  31.     public ConcreteHandler2(Handler successor){
  32.         super(successor);
  33.     }
  35.     @Override
  36.     protected void handleRequest(Request request){
  37.         if(request.getType() = RequestType.TYPE2){
  38.             System.out.println(request.getName() + " is handle by ConcreteHandler2");
  39.             return;
  40.         }
  41.         if(successor != null){
  42.             successor.handleRequest(request);
  43.         }
  44.     }
  45. }
  48. public class Request{
  49.     private RequestType type;
  50.     private String name;
  52.     public Request(RequestType type, String name){
  53.         this.type = type;
  54.         this.anme = name;
  55.     }
  57.     public RequestType getType(){
  58.         return type;
  59.     }
  61.     public String getName(){
  62.         return name;
  63.     }
  64. }
  67. public enum RequestType{
  68.     TYPE1, TYPE2;
  69. }
  72. public class Client{
  73.     public static void main(String[] args){
  74.         Handler handler1 = new ConcreteHandler1(null);
  75.         Handler handler2 = new ConcreteHandler2(handler1);
  77.         Request request1 = new Request(RequestType.TYPE1, "request1");
  78.         handler2.handleRequest(request1);
  80.         Request request2 = new Request(RequestType.TYPE2, "request2");
  81.         handler2.handleRequest(request2);
  82.     }
  83. }
  86. 运行结果
  87. request1 is handle by ConcreteHandler1
  88. request2 is handle by ConcreteHandler2

JDK中的体现