java在filter中修改一个http请求的返回内容(转)

response保存了请求的返回信息,里面有个outputstream,你要返回给页面的流,都在这个地方保存. 
之前遇到一个问题,想把outputstream修改一下.因为这是个输出流,想要改这个里面的东西不是这么简单的. 
sun为我们提供了这么一个工具HttpServletResponseWrapper抽象类,利用这个类的子类把servletresponse包装一下,在过滤器中使用,就可以去除response的文件流,对其作出修改.给出一个实现: 

package com.ali.report.birt.filter;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

public class CharResponseWrapper extends HttpServletResponseWrapper {
    private ByteArrayOutputStream buffer=null;
    private ServletOutputStream out=null;
    private PrintWriter writer=null;

    public CharResponseWrapper(HttpServletResponse resp) throws IOException{
        super(resp);
        buffer=new ByteArrayOutputStream();//真正存储数据的流
        out=new WapperedOutputStream(buffer);
        writer=new PrintWriter(new OutputStreamWriter(buffer,this.getCharacterEncoding()));
    }
    //重载父类获取outputstream的方法
    @Override
    public ServletOutputStream getOutputStream()throws IOException{
        return out;
    }
    //重载父类获取writer的方法
    @Override
    public PrintWriter getWriter() throws UnsupportedEncodingException{
        return writer;
    }
    //重载父类获取flushBuffer的方法
    @Override
    public void flushBuffer()throws IOException{
        if(out!=null){
            out.flush();
        }
        if(writer!=null){
            writer.flush();
        }
    }
    @Override
    public void reset(){
        buffer.reset();
    }
    public String getContent()throws IOException{
        flushBuffer();//将out、writer中的数据强制输出到WapperedResponse的buffer里面，否则取不到数据
        return new String(buffer.toByteArray());
    }

    //内部类，对ServletOutputStream进行包装
    private class WapperedOutputStream extends ServletOutputStream{
        private ByteArrayOutputStream bos=null;
        public WapperedOutputStream(ByteArrayOutputStream stream) throws IOException{
            bos=stream;
        }
        @Override
        public void write(int b) throws IOException{
            bos.write(b);
        }
    }

}

然后在你的过滤器中这么使用: 

public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

            CharResponseWrapper crw = new CharResponseWrapper((HttpServletResponse)response);

            chain.doFilter(request, crw);

            String content = crw.getContent();//response流的内容

            //此处可以对content做处理,然后再把content写回到输出流中
            response.setContentLength(-1);

            PrintWriter out = response.getWriter();

            content = this.changeContent(content, sessionid, folder);

            out.write(content);

            out.flush();

            out.close();*/

                }

如此这般就可以达到你的目的了,当然扩展一下还是可以干很多事的,比如说压缩图片,改变字符集..........