替换禁用语（指定关键字）的过滤器（StopWordsFilter）

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        通用的用户登录过滤器（SessionFilter）

        设置不使用缓存的过滤器（ClearCacheFilter）

        设置站点黑名单的过滤器（BannedAccessFilter）

        将响应数据进行压缩处理的过滤器（CompressionFilter）

        替换禁用语（指定关键字）的过滤器（StopWordsFilter）

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。

 <!--替换关键字的过滤器配置  开始 -->
  <filter>
  <filter-name>StopWordsFilter</filter-name>
  <filter-class>com.hmw.filter.StopWordsFilter</filter-class>
  <init-param>
      <description>需要禁用的关键字，一个关键字占一行</description>
      <param-name>keys</param-name>
      <param-value>
        QQ
        百度
        七一五
      </param-value>
  </init-param>
  </filter>
  
  <filter-mapping>
  <filter-name>StopWordsFilter</filter-name>
  	<servlet-name>*.jsp</servlet-name>
  </filter-mapping>
 <!--替换关键字的过滤器  结束 -->

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 何明旺
 */
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.
	 * <P>
	 * 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.
	 * <P>
	 * 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.
	 * <P>
	 * Be sure <B>not</B> 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();
	}
}