职责链模式(Chain of Responsibility)（对象行为型）

参考文档：

1.设计模式-可复用面向对象软件的基础

2.http://blog.csdn.net/hguisu/article/details/7547231（设计模式 ( 十二 ) 职责链模式(Chain of Responsibility)（对象行为型））

职责链模式(Chain of Responsibility)（对象行为型）

在这里讲的是书中实现的案例。

先看一下这个责任链模式的结构：



一个典型的对象结构可能如下图所示：



这一模式的想法是，给多个对象处理一个请求的机会，从而解耦发送者和接受者。该请求沿对象链传递直至其中一个对象处理它，如下图所示。



下面的交互框图(diagram) 说明了帮助请求怎样沿链传递:



代码实现：

下面的例子举例说明了在一个像前面描述的在线帮助系统中，职责链是如何处理请求的。

HelpHandler.java:

package com.rick.designpattern.chain_of_responsibility;

/**
* Created by MyPC on 2017/6/16.
*/
public class HelpHandler {
public static final int NO_HELP_TOPIC = -1;

private HelpHandler successor;
private int topic;

public HelpHandler(HelpHandler helpHandler, int topic) {
this.successor = helpHandler;
this.topic = topic;
}

public void setHandler(HelpHandler h, int topic) {
this.successor = h;
this.topic = topic;
}

public boolean hasHelp() {
return topic != NO_HELP_TOPIC;
}

public void handleHelp() {
if (null != successor) {
successor.handleHelp();
}
}
}

Widget.java:

package com.rick.designpattern.chain_of_responsibility;

/**
* Created by MyPC on 2017/6/16.
*/
public class Widget extends HelpHandler {

public Widget(Widget parent, int topic) {
super(parent, topic);
}
}

Dialog.java:

package com.rick.designpattern.chain_of_responsibility;

/**
* Created by MyPC on 2017/6/16.
*/
public class Dialog extends Widget {

public Dialog(HelpHandler helpHandler, int topic) {
super(null, topic);
setHandler(helpHandler, topic);
}

@Override
public void handleHelp() {
if (hasHelp()) {
System.out.println("Dialog is handleHelp");
} else {
super.handleHelp();
}
}
}

Button.java:

package com.rick.designpattern.chain_of_responsibility;

/**
* Created by MyPC on 2017/6/16.
*/
public class Button extends Dialog {

public Button(Dialog parent, int topic) {
super(parent, topic);
}

@Override
public void handleHelp() {
if (hasHelp()) {
System.out.println("Button is handleHelp");
} else {
super.handleHelp();
}
}
}

Application.java:

package com.rick.designpattern.chain_of_responsibility;

/**
* Created by MyPC on 2017/6/16.
*/
public class Application extends HelpHandler {
public Application(int topic) {
super(null, topic);
}

@Override
public void handleHelp() {
System.out.println("Application is handleHelp");
}
}

Client.java:

package com.rick.designpattern.chain_of_responsibility;

import com.rick.designpattern.visitor.PricingVisitor;

/**
* Created by MyPC on 2017/6/16.
*/
public class Client {
public static final int PRINT_TOPIC = 1, PAPER_ORIENTATION_TOPIC = 2, APPLICATION_TOPIC = 3;

public static void main(String[] args) {
Application application = new Application(APPLICATION_TOPIC);
Dialog dialog = new Dialog(application, PRINT_TOPIC);
Button button = new Button(dialog, HelpHandler.NO_HELP_TOPIC);

button.handleHelp();
}
}