本系列文章导读：
功能描述
将请求响应中所有的禁用关键字替换掉之后再输出。
使用方法
在 java web 项目的 web.xml 文件中添加如下代码。
StopWordsFilter com.hmw.filter.StopWordsFilter 需要禁用的关键字，一个关键字占一行 keys QQ 百度 七一五 StopWordsFilter *.jsp
过滤器源码
ReplaceKeyWordFilter.java
package com.hmw.filter;import java.io.IOException;import java.io.PrintWriter;import java.util.HashSet;import java.util.Iterator;import java.util.Set;import java.util.StringTokenizer;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.HttpServletResponse;/** * 替换关键字的滤器 * * @author */public class StopWordsFilter implements Filter { private Set keyWords = new HashSet(); /** * 将需要进行替换的关键字添加到一个定义好的 Set 中 */ @Override public void init(FilterConfig config) throws ServletException { String keys = config.getInitParameter("keys"); StringTokenizer tokenizer = new StringTokenizer(keys); String token = null; while (tokenizer.hasMoreTokens()) { token = tokenizer.nextToken(); if(token != null && token.length() > 0){ keyWords.add(tokenizer.nextToken()); } } } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException { CharArrayWrapper responseWrapper = new CharArrayWrapper( (HttpServletResponse) response); // 调用请求资源（使用自己包装的 responseWrapper） chain.doFilter(request, responseWrapper); // 取得响应字符串 String responseString = responseWrapper.toString(); // 将需要替换的关键字用“**”替换掉 Iterator iter = keyWords.iterator(); while (iter.hasNext()) { responseString = replace(responseString, iter.next(), "**"); } // 修改响应头信息中的 Content-Length response.setContentLength(responseString.length()); PrintWriter out = response.getWriter(); out.write(responseString); } @Override public void destroy() { } /** * 将字符串中的所有的指定子字符串替换掉 * @param mainString 需要进行替换的字符串 * @param orig 需要被替换的子串 * @param replacement 替换后的新串 * @return 返回替换后的字符串 */ public static String replace(String mainString, String orig, String replacement) { String result = ""; int oldIndex = 0; int index = 0; int origLength = orig.length(); while ((index = mainString.indexOf(orig, oldIndex)) != -1) { result = result + mainString.substring(oldIndex, index) + replacement; oldIndex = index + origLength; } result = result + mainString.substring(oldIndex); return result; }} CharArrayWrapper.java
package com.hmw.filter;import java.io.CharArrayWriter;import java.io.PrintWriter;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpServletResponseWrapper;/** * A response wrapper that takes everything the client would normally output and * saves it in one big character array. */public class CharArrayWrapper extends HttpServletResponseWrapper { private CharArrayWriter charWriter; /** * Initializes wrapper. * * First, this constructor calls the parent constructor. That call is * crucial so that the response is stored and thus setHeader, *setStatus, * addCookie, and so forth work normally. *
* Second, this constructor creates a CharArrayWriter that will be used to * accumulate the response. */ public CharArrayWrapper(HttpServletResponse response) { super(response); charWriter = new CharArrayWriter(); } /** * When servlets or JSP pages ask for the Writer, don't give them the real * one. Instead, give them a version that writes into the character array. * The filter needs to send the contents of the array to the client (perhaps * after modifying it). */ @Override public PrintWriter getWriter() { return new PrintWriter(charWriter); } /** * Get a String representation of the entire buffer. *
* Be sure not to call this method multiple times on the same * wrapper. The API for CharArrayWriter does not guarantee that it * "remembers" the previous value, so the call is likely to make a new * String every time. */ @Override public String toString() { return charWriter.toString(); } /** Get the underlying character array. */ public char[] toCharArray() { return charWriter.toCharArray(); }}