服务器使用Gzip压缩数据，加快网络传输

        服务器使用Gzip压缩数据，加快网络传输，提高页面性能。使用方法也很简单，在web.xml进行过滤器的配置即可，如下所示。

<filter>
    <filter-name>gzipFilter</filter-name>  
    <filter-class>
        net.sf.ehcache.constructs.web.filter.GzipFilter
    </filter-class>
</filter>
<filter-mapping>
    <filter-name>gzipFilter</filter-name>
    <url-pattern>*.js</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>gzipFilter</filter-name>
    <url-pattern>*.html</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>gzipFilter</filter-name>
    <url-pattern>*.gif</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>gzipFilter</filter-name>
    <url-pattern>*.css</url-pattern>
</filter-mapping>

        当然，还要引入相关的两个jar包，ehcache-web-2.0.4.jar和ehcache.jar。

        使用gzip，首先要设置请求消息头Accept-Encoding为gzip。这样，你将会得到一个响应，根据消息头Content-Encoding为gzip你可以知道，传输过来的数据是经过gzip压缩的。另外，消息头Content-Length会告诉你压缩后的数据长度。

        反编译看到GzipFilter.java的doFilter方法如下，有设置Content-Length。

protected void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
  throws Exception
{
  if ((!(isIncluded(request))) && (acceptsEncoding(request, "gzip")) && (!(response.isCommitted())))
  {
    if (LOG.isDebugEnabled()) {
      LOG.debug(request.getRequestURL() + ". Writing with gzip compression");
    }

    ByteArrayOutputStream compressed = new ByteArrayOutputStream();
    GZIPOutputStream gzout = new GZIPOutputStream(compressed);

    GenericResponseWrapper wrapper = new GenericResponseWrapper(response, gzout);
    wrapper.setDisableFlushBuffer(true);
    chain.doFilter(request, wrapper);
    wrapper.flush();

    gzout.close();

    if (response.isCommitted()) {
      return;
    }

    switch (wrapper.getStatus())
    {
    case 204:
    case 205:
    case 304:
      return;
    }

    byte[] compressedBytes = compressed.toByteArray();
    boolean shouldGzippedBodyBeZero = ResponseUtil.shouldGzippedBodyBeZero(compressedBytes, request);
    boolean shouldBodyBeZero = ResponseUtil.shouldBodyBeZero(request, wrapper.getStatus());
    if ((shouldGzippedBodyBeZero) || (shouldBodyBeZero))
    {
      response.setContentLength(0);
      return;
    }

    ResponseUtil.addGzipHeader(response);

    if (this.setVaryHeader) {
      ResponseUtil.addVaryAcceptEncoding(wrapper);
    }

    response.setContentLength(compressedBytes.length);

    response.getOutputStream().write(compressedBytes);
  }
  else
  {
    if (LOG.isDebugEnabled()) {
      LOG.debug(request.getRequestURL() + ". Writing without gzip compression because the request does not accept gzip.");
    }
    chain.doFilter(request, response);
  }
}

        进一步看ResponseUtil.addGzipHeader方法，有设置消息头Content-Encoding为gzip。

public static void addGzipHeader(HttpServletResponse response)
  throws ResponseHeadersNotModifiableException
{
  response.setHeader("Content-Encoding", "gzip");
  boolean containsEncoding = response.containsHeader("Content-Encoding");
  if (!(containsEncoding))
    throw new ResponseHeadersNotModifiableException("Failure when attempting to set Content-Encoding: gzip");
}

        配置好后，要在浏览器端验证是否做了压缩，可以安装http Watch工具，在IE浏览器中查看，如下所示。

        未配置gzip压缩前：

        配置gzip压缩后：可以看到压缩比例

PS：网上看到用Java实现的gzip

GetMethod method = new GetMethod(url);//生成一个get方法实例  
  
method.setQueryString(queryString);//设置查询字符串  
method.addRequestHeader("Accept-Encoding", "gzip");//设置接受响应消息为gzip  
  
HttpClient client = new HttpClient();//生成执行get方法的客户端实例  
client.executeMethod(method);//执行get方法  
  
InputStream in = method.getResponseBodyAsStream();//获取响应消息体  
Header contentEncoding = method.getResponseHeader("Content-Encoding");//获取消息头Content-Encoding判断数据流是否gzip压缩过  
  
if (contentEncoding != null && contentEncoding.getValue().equalsIgnoreCase("gzip")) {  
    GZIPInputStream gzipIn = new GZIPInputStream(in);  
    int len = Integer.parseInt(method.getResponseHeader("Content-Length").getValue());  
    byte[] b = new byte[len];  
    gzipIn.read(b);  
      
    String json = new String(b);  
    System.out.println(json);  
}

        使用gzip在服务器端压缩数据的例子

byte[] result = data.getBytes("UTF-8");  
  
if(response.getHeader("Accept-Encoding").equalsIgnoreCase("gzip"))  
{  
    // System.out.println("Before compression, the data size is ："+ result.length);  
    // Using gzip compress the data  
    ByteArrayOutputStream out = new ByteArrayOutputStream();  
    GZIPOutputStream gout = new GZIPOutputStream(out);  
    gout.write(json.getBytes("UTF-8"));  
    gout.close();  
    result = out.toByteArray();  
  
    // System.out.println("After compression, the data size is "+gzipResult.length);  
    this.getResp().setHeader("Content-Encoding","gzip");  
    this.getResp().setHeader("Content-Length", result.length+"");  
}  
  
response.getOutputStream().write(result);  

 

参考文章：http://blog.csdn.net/hpli148/article/details/7468573