一个简单的数据压缩过滤器

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

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;


public class GZIPEncodeTest implements Filter {

public void init(FilterConfig filterConfig) {
}

public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain chain) throws IOException, ServletException {
  
  String transferEncoding = getGZIPEncoding((HttpServletRequest) request);
  if (transferEncoding == null) {
   chain.doFilter(request, response);
  } else {
   ((HttpServletResponse) response).setHeader("Content-Encoding",
     transferEncoding);
   GZIPEncodableResponse wrappedResponse = new GZIPEncodableResponse(
     (HttpServletResponse) response);
   chain.doFilter(request, wrappedResponse);
   wrappedResponse.flush();
  }
}

public void destroy() {
}

private static String getGZIPEncoding(HttpServletRequest request) {
  String acceptEncoding = request.getHeader("Accept-Encoding");
  if (acceptEncoding == null)
   return null;
  acceptEncoding = acceptEncoding.toLowerCase();
  if (acceptEncoding.indexOf("x-gzip") >= 0) {
   return "x-gzip";
  }
  if (acceptEncoding.indexOf("gzip") >= 0) {
   return "gzip";
  }
  return null;
}

private class GZIPEncodableResponse extends HttpServletResponseWrapper {
  private GZIPServletStream wrappedOut;

  public GZIPEncodableResponse(HttpServletResponse response)
    throws IOException {
   super(response);
   wrappedOut = new GZIPServletStream(response.getOutputStream());
  }

  public ServletOutputStream getOutputStream() throws IOException {
   return wrappedOut;
  }

  private PrintWriter wrappedWriter;

  public PrintWriter getWriter() throws IOException {
   if (wrappedWriter == null) {
    wrappedWriter = new PrintWriter(new OutputStreamWriter(
      getOutputStream(), getCharacterEncoding()));
   }
   return wrappedWriter;
  }

  public void flush() throws IOException {
   if (wrappedWriter != null) {
    wrappedWriter.flush();
   }
   wrappedOut.finish();
  }
}

private class GZIPServletStream extends ServletOutputStream {
  private GZIPOutputStream outputStream;

  public GZIPServletStream(OutputStream source) throws IOException {
   outputStream = new GZIPOutputStream(source);
  }

  public void finish() throws IOException {
   outputStream.finish();
  }

  public void write(byte[] buf) throws IOException {
   outputStream.write(buf);
  }

  public void write(byte[] buf, int off, int len) throws IOException {
   outputStream.write(buf, off, len);
  }

  public void write(int c) throws IOException {
   outputStream.write(c);
  }

  public void flush() throws IOException {
   outputStream.flush();
  }

  public void close() throws IOException {
   outputStream.close();
  }
}
}

<filter>
     <description>Here is  'response to data compression' filters  </description>
     <filter-name>GZIPEncoder   </filter-name>
     <filter-class>com.jsptw.filter.GZIPEncodeFilter</filter-class>
</filter>

<filter-mapping>
      <filter-name>GZIPEncoder</filter-name>
      <url-pattern>/*</url-pattern>
</filter-mapping>

/*

public static void main(String[] args) throws Exception {
  HttpClient http = new HttpClient();
  GetMethod get = new GetMethod("http://localhost:8080/games/backgroundIndex.jsp");
  try {
   get.addRequestHeader("accept-encoding", "gzip,deflate");
   get
     .addRequestHeader(
       "user-agent",
       "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; Alexa Toolbar; Maxthon 2.0)");
   int er = http.executeMethod(get);
   if (er == 200) {
    String html = get.getResponseBodyAsString();
    System.out.println("页面压缩后的代码："+html);
    System.out.println("压缩后的页面数据大小："+html.getBytes().length);
   }
  } finally {
   get.releaseConnection();
  }
}