责任链模式（Chain of Responsibility）

    职责链模式：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受者之间的耦合关系。将这个对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理他为止。

    针对如下需求，有一个字符串过滤链，需要过滤字符串中的某些字符，如要把“<>”替换为“{}”，“天朝”替换为“中国”等操作。

    可以先定义一个接口：

public interface Filter {String doFilter(String str);}

    然后针对需求，实现不同的实现类：

public class AFilter implements Filter {@Overridepublic String doFilter(String str) {String r = str.replace('<', '{')   .replace('>', '}');return r;}}

public class BFilter implements Filter {@Overridepublic String doFilter(String str) {String r = str.replace("天朝", "中国");return r;}}

    定义链条：

public class FilterChain implements Filter {List<Filter> filters = new ArrayList<Filter>();public FilterChain addFilter(Filter f) {this.filters.add(f);return this;}public String doFilter(String str) {String r = str;for(Filter f: filters) {r = f.doFilter(r);}return r;}}

     但是此上的职责链灵活性并不够，可以针对多个处理类对象，每个对象持有对下一个对象的引用，形成一条链，请求在这条链上传递，直到某一对象决定处理该请求。

    如下的例子：

public interface IHandle {public abstract void operator(String mesg);public abstract void addChain(IHandle h);public abstract IHandle getChain();}public class Manager implements IHandle {private IHandle nextChain = null;private String responsibility = "Get Project";@Overridepublic void operator(String mesg) {if (mesg.equals(responsibility)) {System.out.println("A manager  -->  Get a Project");} else {if (nextChain != null) {nextChain.operator(mesg);}}}@Overridepublic void addChain(IHandle h) {nextChain = h;}@Overridepublic IHandle getChain() {return nextChain;}}public class Programmer implements IHandle {private IHandle nextChain = null;private String responsibility = "Coding";@Overridepublic void operator(String mesg) {if (mesg.equals(responsibility)) {System.out.println("A Programmer  -->  Coding");} else {if (nextChain != null) {nextChain.operator(mesg);}}}@Overridepublic void addChain(IHandle h) {nextChain = h;}@Overridepublic IHandle getChain() {return nextChain;}}public class ProjectManager implements IHandle {private IHandle nextChain = null;private String responsibility = "Design";@Overridepublic void operator(String mesg) {if (mesg.equals(responsibility)) {System.out.println("A PM  -->  Design");} else {if (nextChain != null) {nextChain.operator(mesg);}}}@Overridepublic void addChain(IHandle h) {nextChain = h;}@Overridepublic IHandle getChain() {return nextChain;}}public class Test {public static void main(String[] args) {Manager manager = new Manager();ProjectManager pm = new ProjectManager();Programmer programmer = new Programmer();manager.addChain(pm);pm.addChain(programmer);manager.operator("Get Project");manager.operator("Design");manager.operator("Coding");}}

    或则采取如下的结构：

public abstract class Chain {protected Chain nextChain;public abstract void doChain(Object vo);public void setChain(Chain nextChain){this.nextChain = nextChain;}protected void sendNextChain(Object vo){if(nextChain !=null){nextChain.doChain(vo);}}}

     但是，如果不是单向链呢？比如数据从A链到B链处理后，希望处理的结果由B链经A连返回出来（类似计算机网络的五层结构的数据流向）。例子如下:

public class Request {String requestStr;public String getRequestStr() {return requestStr;}public void setRequestStr(String requestStr) {this.requestStr = requestStr;}}public class Response {String responseStr;public String getResponseStr() {return responseStr;}public void setResponseStr(String responseStr) {this.responseStr = responseStr;}}public interface Filter {void doFilter(Request request, Response response, FilterChain chain);}public class AFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {request.requestStr = request.requestStr.replace('<', '{')   .replace('>', '}');chain.doFilter(request, response, chain);response.responseStr += "---AFilter()";}}public class BFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {request.requestStr = request.requestStr.replace("天朝", "中国");chain.doFilter(request, response, chain);response.responseStr += "---BFilter()";}}public class FilterChain implements Filter {List<Filter> filters = new ArrayList<Filter>();int index = 0;public FilterChain addFilter(Filter f) {this.filters.add(f);return this;}@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {if(index == filters.size()) return ;Filter f = filters.get(index);index ++;f.doFilter(request, response, chain);}}public class Main {public static void main(String[] args) {String msg = "*********************";Request request = new Request();request.setRequestStr(msg);Response response = new Response();response.setResponseStr("response");FilterChain fc = new FilterChain();fc.addFilter(new AFilter())  .addFilter(new BFilter())  ;fc.doFilter(request, response, fc);System.out.println(request.getRequestStr());System.out.println(response.getResponseStr());}}