责任链模式----ChainOfResponsibility

意图：避免请求发送者与接收者耦合在一起，让多个对象都有可能接收请求，将这些对象连接成一条链，

并且沿着这条链传递请求，直到有对象处理它为止
主要解决：职责链上的处理者负责处理请求，客户只需要将请求发送到职责链上即可，无须关心请求的处

理细节和请求的传递，所以职责链将请求的发送者和请求的处理者解耦了
什么时候使用：在处理消息的时候以过滤很多道
如何解决 ：拦截的类都实现统一接口

应用实例：1、红楼梦中的“击鼓传花”2、JS中的事件冒泡 3、JAVA WEB中 Apache Tomcat 的对Encoding的 处理，

Struts2 的拦截器， jsp servlet 的Filte

1. package com.bjsxt.dp.filter;
   
   public interface Filter {
   	void doFilter(Request request, Response response, FilterChain chain);
   }
   

   
   

   package com.bjsxt.dp.filter;
   
   public class Request {
   	String requestStr;
   
   	public String getRequestStr() {
   		return requestStr;
   	}
   
   	public void setRequestStr(String requestStr) {
   		this.requestStr = requestStr;
   	}
   }
   

   
   

   package com.bjsxt.dp.filter;
   
   public class Response {
   	String responseStr;
   
   	public String getResponseStr() {
   		return responseStr;
   	}
   
   	public void setResponseStr(String responseStr) {
   		this.responseStr = responseStr;
   	}
   	
   }
   

   
   

   package com.bjsxt.dp.filter;
   
   import java.util.ArrayList;
   import java.util.List;
   
   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;
   	}
   	
   	@Override
   	public void doFilter(Request request, Response response, FilterChain chain) {
   		if(index == filters.size()) return ;
   		
   		Filter f = filters.get(index);
   		index ++;
   		f.doFilter(request, response, chain);
   	}
   }
   

   
   

   package com.bjsxt.dp.filter;
   
   public class HTMLFilter implements Filter {
   
   	
   	@Override
   	public void doFilter(Request request, Response response, FilterChain chain) {
   		//process the html tag <>
   		request.requestStr = request.requestStr.replace('<', '[')
   				   .replace('>', ']') + "---HTMLFilter()";
   		chain.doFilter(request, response, chain);
   		response.responseStr += "---HTMLFilter()";
   	}
   
   }
   

   
   

   package com.bjsxt.dp.filter;
   
   public class SesitiveFilter implements Filter {
   
   	@Override
   	public void doFilter(Request request, Response response, FilterChain chain) {
   		request.requestStr = request.requestStr.replace("被就业", "就业")
   		 .replace("敏感", "") + "---SesitiveFilter()";
   		chain.doFilter(request, response, chain);
   		response.responseStr += "---SesitiveFilter()";
   	
   	}
   }
   

2. 
   

   package com.bjsxt.dp.filter;
   
   public class Main {
   
   	/**
   	 * @param args
   	 */
   	public static void main(String[] args) {
   		String msg = "大家好:)，<script>，敏感，被就业，网络授课没感觉，因为看不见大家伙儿";
   		Request request = new Request();
   		request.setRequestStr(msg);
   		Response response = new Response();
   		response.setResponseStr("response");
   		FilterChain fc = new FilterChain();
   		fc.addFilter(new HTMLFilter())
   		  .addFilter(new SesitiveFilter());
   		
   		fc.doFilter(request, response, fc);
   		System.out.println(request.getRequestStr());
   		System.out.println(response.getResponseStr());
   	}
   
   }