责任链(Chain Of Responsibility)

Intent

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为止。

Class Diagram

  • Handler:定义处理请求的接口,并且实现后继链(successor)

Implementation

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public abstract class Handler {

protected Handler successor;


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


protected abstract void handleRequest(Request request);
}
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public class ConcreteHandler1 extends Handler {

public ConcreteHandler1(Handler successor) {
super(successor);
}


@Override
protected void handleRequest(Request request) {
if (request.getType() == RequestType.TYPE1) {
System.out.println(request.getName() + " is handle by ConcreteHandler1");
return;
}
if (successor != null) {
successor.handleRequest(request);
}
}
}
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public class ConcreteHandler2 extends Handler {

public ConcreteHandler2(Handler successor) {
super(successor);
}


@Override
protected void handleRequest(Request request) {
if (request.getType() == RequestType.TYPE2) {
System.out.println(request.getName() + " is handle by ConcreteHandler2");
return;
}
if (successor != null) {
successor.handleRequest(request);
}
}
}
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public class Request {

private RequestType type;
private String name;


public Request(RequestType type, String name) {
this.type = type;
this.name = name;
}


public RequestType getType() {
return type;
}


public String getName() {
return name;
}
}
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public enum RequestType {
TYPE1, TYPE2
}
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public class Client {

public static void main(String[] args) {

Handler handler1 = new ConcreteHandler1(null);
Handler handler2 = new ConcreteHandler2(handler1);

Request request1 = new Request(RequestType.TYPE1, "request1");
handler2.handleRequest(request1);

Request request2 = new Request(RequestType.TYPE2, "request2");
handler2.handleRequest(request2);
}
}
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request1 is handle by ConcreteHandler1
request2 is handle by ConcreteHandler2

JDK

源码:https://github.com/HWYWL/design-patterns