设计模式之责任链模式

责任链（Chain of Responsibility）模式
   责任链模式是一种对象的行为模式。在责任链模式里，很多对象由每一个对象对其下家的引用而连接起来形成一条链。请求在这个链上传递，直到链上的某一个对象决定处理此请求。发出这个请求的客户端并不知道链上的哪一个对象最终处理这个请求，这使得系统可以在不影响客户端的情况下动态地重新组织和分配责任。

  GoF对职责链模式的定义为：为了避免请求的发送者和接收者之间的耦合关系，使多个接受对象都有机会处理请求。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

java Web中用到的比较多，比如开发中常用到的Filter和struts2的interceptor.

下面是一个模仿web过滤器的java简单实现,采用责任链模式。

首先测试类：
 

  package com.ihyperwin.designPattern.chainOfResponsibility;

public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
		String msg = "<script>全部为中文或者小写英文，ABC123qwertyuiop";
		Request request = new Request();
		Response response = new Response();
		request.setRequestString(msg);
		response.setResponseString("");
		HtmlFilter htmlFilter = new HtmlFilter();
		CaseFilter caseFilter = new CaseFilter();
		FilterChain filterChain = new FilterChain();
		filterChain.addFilter(htmlFilter);
		filterChain.addFilter(caseFilter);
		filterChain.doFilter(request, response, filterChain);//开始过滤
		
		System.out.println("requstString is "+request.getRequestString());
		System.out.println("responseString is "+response.getResponseString());
		

	}

}

/**
 * 
 */
package com.ihyperwin.designPattern.chainOfResponsibility;

/**
 * @author ihyperwin
 * 模拟请求类
 */
public class Request {
	
	private String requestString;

	public Request() {
		super();
	}

	public String getRequestString() {
		return requestString;
	}

	public void setRequestString(String requestString) {
		this.requestString = requestString;
	}

}

/**
 * 
 */
package com.ihyperwin.designPattern.chainOfResponsibility;

/**
 * @author ihyperwin
 * 模拟返回响应类
 */
public class Response {
	
	private String responseString;

	public Response() {
		super();
	}

	public String getResponseString() {
		return responseString;
	}

	public void setResponseString(String responseString) {
		this.responseString = responseString;
	}
	
	


}

/**
 * 
 */
package com.ihyperwin.designPattern.chainOfResponsibility;

/**
 * @author ihyperwin
 * 过滤器接口
 */
public interface Filter {
	
	void doFilter(Request request,Response response,FilterChain filterChain);

}

/**
 * 
 */
package com.ihyperwin.designPattern.chainOfResponsibility;

/**
 * @author ihyperwin
 * 把大写英文字母转换成小写的过滤器类
 */
public class CaseFilter implements Filter{

	@Override
	public void doFilter(Request request, Response response,
			FilterChain filterChain) {
		
		request.setRequestString(request.getRequestString().toLowerCase()+"#CaseFilter");
		filterChain.doFilter(request, response, filterChain);
		response.setResponseString(response.getResponseString()+"#CaseFilter");
		
	}

	
	

}

/**
 * 
 */
package com.ihyperwin.designPattern.chainOfResponsibility;

/**
 * @author ihyperwin
 * 转换非法html字符的过滤器类
 */
public class HtmlFilter implements Filter{

	@Override
	public void doFilter(Request request, Response response,
			FilterChain filterChain) {
		
		request.setRequestString(request.getRequestString().replace("<", "&lt;").replace(">", "&gt;")+"#htmlFilter");
		filterChain.doFilter(request, response, filterChain);
		response.setResponseString(response.getResponseString()+"#htmlFilter");
	}

	
	

}

/**
 * 
 */
package com.ihyperwin.designPattern.chainOfResponsibility;

import java.util.ArrayList;
import java.util.List;

/**
 * @author ihyperwin
 * 过滤器链
 */
public class FilterChain implements Filter{
	
	private List<Filter> filterList = new ArrayList<Filter>();
	
	private int index = 0;
	
	public FilterChain addFilter(Filter filter){
		filterList.add(filter);
		return this;
	}

	@Override
	public void doFilter(Request request, Response response,
			FilterChain filterChain) {
		if(filterList.size()<=0) return;
		if(index>=filterList.size()) return;
		Filter filter = filterList.get(index);
		index++;
		filter.doFilter(request, response, filterChain);
		
		
	}
	
	

}