责任链模式（Chain Of Responsibility）

1 概念

1、定义

• 为请求创建了一个接受者对象的链。

2、应用场景

• 一个请求的处理需要多个对象当中的一个或几个协作处理。

3、优点

• 请求的发送者和接受者解耦。
• 可以控制执行顺序。
• 符合开闭原则和单一职责原则。

4、源码中的应用

• javax.servlet.Filter
• javax.servlet.FilterChain

2 实现

package com.xianhuii.designpattern;

public class ChainOfResponsibilityTest {
    public static void main(String[] args) {
        Request request = new Request(true, false, true, true);
        RequestFrequentHandler requestFrequentHandler = new RequestFrequentHandler(new LoggingHandler(null));
        if (requestFrequentHandler.process(request)) {
            System.out.println("正常业务处理");
        } else {
            System.out.println("访问异常");
        }
    }
}

class Request {
    private boolean loggedOn;
    private boolean frequentOk;
    private boolean isPermits;
    private boolean containsSensitiveWords;
    private String requestBody;

    public Request(boolean loggedOn, boolean frequentOk, boolean isPermits, boolean containsSensitiveWords) {
        this.loggedOn = loggedOn;
        this.frequentOk = frequentOk;
        this.isPermits = isPermits;
        this.containsSensitiveWords = containsSensitiveWords;
    }

    public boolean isLoggedOn() {
        return loggedOn;
    }

    public boolean isFrequentOk() {
        return frequentOk;
    }

    public boolean isPermits() {
        return isPermits;
    }

    public boolean isContainsSensitiveWords() {
        return containsSensitiveWords;
    }
}

abstract class Handler {
    Handler next;

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

    public Handler getNext() {
        return next;
    }

    public void setNext(Handler next) {
        this.next = next;
    }

    abstract boolean process(Request request);
}

class RequestFrequentHandler extends Handler {

    public RequestFrequentHandler(Handler next) {
        super(next);
    }

    @Override
    boolean process(Request request) {
        System.out.println("访问频率控制");
        if (request.isFrequentOk()) {
            Handler next = getNext();
            if (next == null) {
                return true;
            }
            if (!next.process(request)) {
                return false;
            } else {
                return true;
            }
        }
        return false;
    }
}

class LoggingHandler extends Handler {

    public LoggingHandler(Handler next) {
        super(next);
    }

    @Override
    boolean process(Request request) {
        System.out.println("登录验证");
        if (request.isLoggedOn()) {
            Handler next = getNext();
            if (null == next) {
                return true;
            }
            if (!next.process(request)) {
                return false;
            } else {
                return true;
            }
        }
        return false;
    }
}