责任链模式

责任链模式：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收者之间的耦合关系。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。这个定义让我们很自然地联想到了struts中的过滤器，没错，那我们自己创建一个过滤器吧：

package com.jerry.design.chain;

import java.util.HashMap;
import java.util.Map;



	// 测试类
public class Test {

	public static void main(String[] args) {
		Request req = new Request();
		req.setParam("first", "first ok!");
		req.setParam("second", "second ok!");
		req.setParam("third", "third ok!");
		req.setParam("one", "one ok!");
		// 创建指责链的所有节点  
        AbstractHandler handler01 = new FirstFilter();  
        AbstractHandler handler02 = new SecondFilter();  
        AbstractHandler handler03 = new ThirdFilter();  
 
        // 进行链的组装，即头尾相连，一层套一层  
        handler01.setNextHandler(handler02);  
        handler02.setNextHandler(handler03);  
        
        handler01.handleRequest(req);
        
    }
}
class Request {
	
    private Map<String,String> param = new HashMap<String,String>();

	public String getParameter(String string) {
		return (String) param.get(string);
	}

	public void setParam(String key,String value) {
		this.param.put(key, value);
	}
    
    
}

abstract class AbstractHandler {  
    protected AbstractHandler successor;  
    
    //处理请求，由子类完成   
    public abstract void handleRequest(Request request);  
  
    //设置下一个处理请求的人   
    public void setNextHandler(AbstractHandler successor) {  
        this.successor = successor;  
    }  
}  

class FirstFilter extends AbstractHandler {

  @Override
  public void handleRequest(Request request) {
		  System.out.println("当前为第一个处理者，可处理该请求，参数值为："+request.getParameter("first"));
		  successor.handleRequest(request);
  }
}

class SecondFilter extends AbstractHandler {

	  @Override
	  public void handleRequest(Request request) {
			  System.out.println("当前为第二个处理者，可处理该请求，参数值为："+request.getParameter("second"));
			  successor.handleRequest(request);
	  }
}

class ThirdFilter extends AbstractHandler {

	  @Override
	  public void handleRequest(Request request) {
			  System.out.println("当前为第三个处理者，可处理该请求，参数值为："+request.getParameter("third"));
	  }
}