compressionresponsewrapper.java

运用过滤器对请求和响应进行替换

package org.sunxin.ch16.filter;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.zip.GZIPOutputStream;

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

public class CompressionResponseWrapper extends HttpServletResponseWrapper
{

	private GZIPServletOutputStream gzipsos;
	private PrintWriter pw;
	
	public CompressionResponseWrapper(HttpServletResponse response) throws IOException 
	{
		super(response);
		
		//用响应输出流创建GZIPServletOutputStream对象
		gzipsos = new GZIPServletOutputStream(response.getOutputStream());
		////用GZIPServletOutputStream对象作为参数，构造PrintWriter对象
		pw = new PrintWriter(gzipsos);
	}
	
	/**
	 * 重写setContentLength()方法，以避免Content-Length实体报头所指出的长度
	 * 和压缩后的实体正文长度不匹配
	 */
	@Override
	public void setContentLength(int len){}

	@Override
	public ServletOutputStream getOutputStream() throws IOException
	{
		return gzipsos;
	}

	@Override
	public PrintWriter getWriter() throws IOException
	{
		return pw;
	}
	
	/**
	 * 过滤器调用这个方法来得到GZIPOutputStream对象，以便完成将压缩数据写入输出流的操作
	 */
	public GZIPOutputStream getGZIPOutputStream()
	{
		return gzipsos.getGZIPOutputStream();
	}
}