package com.greatest.Filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//自定義HttpFilter方法 ，實現Filter介面
public abstract class MyFilter implements Filter {

	// 用於儲存FilterConfig方法
	private FilterConfig fconfig;

	// 不建議子類直接覆蓋，若直接覆蓋，可能會導致filterconfig成員變數初始化失敗
	@Override
	public void init(FilterConfig Config) throws ServletException {
		this.fconfig = Config;
		init();
	}

	// 供子類繼承的初始化方法 可以通過getFilterConfig（）方法獲取FilterConfig物件
	protected void init() {
		// TODO Auto-generated method stub

	}// 直接返回init(ServletConfig)的FilterConfig物件

	public FilterConfig getFconfig() {
		return fconfig;
	}

	@Override
	public void destroy() {
	}

	// 原聲的doFilter方法 在方法內部把ServletRequest ,ServletResponse轉為了
	// HttpServletRequest 和 HttpSrevletResponse 並呼叫了
	// doFilter(ServletRequest Req, ServletResponse Resp, FilterChain Chain)
	// 若編寫Filter的過濾方法 不建議直接繼承該方法 而建議 繼承
	// public abstract void doFilter(HttpServletRequest
	// request,HttpServletResponse response,
	// FilterChain Chain) 方法
	@Override
	public void doFilter(ServletRequest Req, ServletResponse Resp, FilterChain Chain)
			throws IOException, ServletException {
		HttpServletRequest requesr = (HttpServletRequest) Req;
		HttpServletResponse response = (HttpServletResponse) Resp;

		doFilter(requesr, response, Chain);

	}// 抽像方法 為Http請求定製 必須實現的方法

	public abstract void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain Chain)
			throws IOException, ServletException;

}
 

package com.greatest.Filter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class MyHttpServletRequest extends HttpServletRequestWrapper {
		public MyHttpServletRequest(HttpServletRequest request) {
			super(request);
			// TODO Auto-generated constructor stub
		}
	    @Override
	       //增強方法  不光獲取值  還要判斷  
	    public String getParameter(String name) {
	       String  val=super.getParameter(name);
	       if(val!=null&&val.contains(" fuck ")){
	    	   val=val.replace("fuck", "****");
	       }
	    	return val;
	    }
	}
 

package com.greatest.Filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet Filter implementation class ContentFilter
 */
@WebFilter("/bbs.jsp")
public class ContentFilter extends MyFilter{

	 public void doFilter(HttpServletRequest request,
	    		HttpServletResponse response, FilterChain filterChain)
	    		throws IOException, ServletException {
	    	//1. 獲取請求 content 引數的值
	    	String content = request.getParameter("content");
	    	
	    	System.out.println(request); 
	    	HttpServletRequest req = new MyHttpServletRequest(request);
	    	
	    	//2. 把其中 fuck, shit 等字串替換換為 ****
	    	if(content.contains(" fuck ")){
	    		//SerletRequest, HttpServletRequest 中並沒有提供諸如 setParameter(paramName, paramValue)
	    		//類似於這樣的方法. 
	    		
	    		//目標: 改變 HttpServletRequest 的 getParameter(String) 方法的行為: 若該方法的返回值中
	    		//包含 " fuck ", 則替換為 " **** "
	    		
	    		//1. 若對於一個類的方法不滿意, 需要進行重寫, 最常見的方式是, 繼承父類, 重寫方法. 
	    		//若實現則需要繼承 org.apache.catalina.connector.RequestFacade, 而這僅是 Tomcat
	    		//伺服器的實現, 若更換伺服器, 該方案將無法使用. ×. 
	    		
	    		//2. 直接寫一個 HttpServletRequest 介面的實現類: 無法實現	其中方法. ×
	    		
	    		//3. 裝飾目前的 HttpServletRequest 物件: 裝飾其 getParameter 方法, 而其他方法還和其實現相同.
	    		//建立一個類, 該類實現 HttpServletRequest 介面, 把當前 doFilter 中的 request 傳入到該類中, 作為
	    		//其成員變數, 使用該成員變數去實現介面的全部方法. 
	    		
	    	}
	    	
	    	//3. 轉到目標頁面
	    	filterChain.doFilter(req, response);
	    }
}
 

Content JSP
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="bbs.jsp" method="post">
    content:<textarea rows="5" cols="21" name="content"></textarea>
    <input type="submit" value="Submit"/>
    
    </form>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    content:${param.content } 
    <br><br>
    method:<%=request.getMethod() %>
    <br><br>
    <%=request %>
</body>
</html>