大家好，又见面了，我是你们的朋友全栈君。

通过Filter来实现留言板的敏感词过滤…

思路很简单，我们这里的敏感词是直接先放进去的，实际项目中，肯定是存在数据库中。在Filter 过滤器中，我们先拿到用户提交的留言，如果出现了敏感词，我们就用*号来替换。

代码演示:

index.jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
     <title>过滤器应用示例---敏感词过滤</title>
  </head>

  <body>
     <h2>过滤器应用示例---敏感词过滤</h2>
     <form action="<c:url value='/NoteServlet'/>" method="post">
        用户名:<input type="text" name="name" /><br/><br/>
        <fieldset>
            <legend>留言板</legend>
            <textarea name="note" rows="10" cols="20"></textarea>
        </fieldset>
        <input type="submit" value="留言" />     
     </form>
  </body>
</html>

WordsUtil.java:敏感词集合:

package cn.hncu.pubs;

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

public class WordsUtil { 
   
    private static List<String> list = new ArrayList<String>();
    static{
        //这里应该从数据库中导入敏感词的，我在这里就直接用词来模拟了
        list.add("骂人");
        list.add("sb");
    }
    public static List<String> getWords(){
        return list;
    }
    public static void reBuild(){
       //把list中的内容存储到数据库---每一段时间存储一次
    }
}

NoteServlet.java

package cn.hncu.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class NoteServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.println("不支持GET方式留言");
        out.close();
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
        out.println("<HTML>");
        out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
        out.println(" <BODY>");

        String name = request.getParameter("name");
        if(name==null || name.trim().length()<=0){
            out.println("名字不能为空!!!");
        }else{
            String words = request.getParameter("note");
            out.println("<br/>"+name+"的留言是:<br/>"+ words);
        }
        out.println(" </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }

}

WordFilter.java:敏感词过滤

package cn.hncu.filter;

import java.io.IOException;
import java.util.List;

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.HttpServletRequestWrapper;

import cn.hncu.pubs.WordsUtil;

public class WordFilter implements Filter{ 
   

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");

        //在过滤器中用装饰模式把 原装request的功能增强了
        //---拦截后台调用的getParamter()方法
        MyRequest req = new MyRequest((HttpServletRequest)request);

        chain.doFilter(req, response);//放行
    }

    @Override
    public void destroy() {
    }
}

class MyRequest extends HttpServletRequestWrapper{
    public MyRequest(HttpServletRequest request) {
        super(request);
    }

    @Override
    public String getParameter(String name) {
        String str = super.getParameter(name);
        List<String> list = WordsUtil.getWords();
        for(String word : list){
            str = str.replaceAll(word, "*");
        }
        return str;
    }



}

配置web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name></display-name>
  <filter>
    <filter-name>wordFilter</filter-name>
    <filter-class>cn.hncu.filter.WordFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>wordFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>


  <servlet>
    <servlet-name>NoteServlet</servlet-name>
    <servlet-class>cn.hncu.servlet.NoteServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>NoteServlet</servlet-name>
    <url-pattern>/NoteServlet</url-pattern>
  </servlet-mapping>    
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>