guestbookfilter.java

运用过滤器对请求和响应进行替换

package org.sunxin.ch16.filter;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class GuestbookFilter implements Filter
{
    private static final String WORD_FILE="word_file";
    
    HashMap<String,String> hm=new HashMap<String,String>();
    
    /**
     * 在init()方法中，读取保存了不雅字句和替换内容的文件，
     * 并以不雅字句作为key，替换内容作为value，保存到Hashmap对象中。
     */
    public void init(FilterConfig filterConfig) throws ServletException
    {   
        String configPath=filterConfig.getInitParameter(WORD_FILE);
        
        ServletContext sc=filterConfig.getServletContext();
        String filePath=sc.getRealPath(configPath);
        
        try
        {
            FileReader fr=new FileReader(filePath);
            BufferedReader br=new BufferedReader(fr);
            
            String line;
            while(null!=(line=br.readLine()))
            {
                String[] strTemp=line.split("=");
                hm.put(strTemp[0],strTemp[1]);
            }
        }
        catch(IOException ie)
        {
            throw new ServletException("读取过滤文件信息出错！");
        }
    }
   
    public void doFilter(ServletRequest request,
                         ServletResponse response,
                         FilterChain chain)
                  throws IOException, ServletException
    {
        
        HttpServletRequest httpReq=(HttpServletRequest)request;
        HttpServletResponse httpResp=(HttpServletResponse)response;
        
        //得到请求和响应对象的封装类对象。
        MyRequestWrapper reqWrapper=new MyRequestWrapper(httpReq);
        MyResponseWrapper respWrapper=new MyResponseWrapper(httpResp);
                
        chain.doFilter(reqWrapper,respWrapper);
        
        String content = new String(respWrapper.toByteArray());
        String result=replaceText(content);
        httpResp.setContentType("text/html;charset=GB2312");
        PrintWriter out = httpResp.getWriter();
        out.println(result);
        out.close();
    }
    
    /**
     * 对内容中的不雅字句进行过滤。
     */
    public String replaceText(String content) throws IOException
    {
        StringBuffer sb=new StringBuffer(content);
        Set<String> keys=hm.keySet();
        Iterator<String> it=keys.iterator();
        while(it.hasNext())
        {
            String key=(String)it.next();
            int index=sb.indexOf(key);
            while(-1!=index)
            {
                sb.replace(index,index+key.length(),(String)hm.get(key));
                index=sb.indexOf(key);
            }
        }
        return sb.toString();
        
    }
    public void destroy(){}
}