Gzip压缩优化网站

网站常使用GZIP压缩算法对网页内容进行压缩，然后传给浏览器，以减小数据传输量，提高响应速度。浏览器接收到GZIP压缩数据后会自动解压并正确显示。GZIP加速常用于解决网速慢的瓶颈。

压缩Filter中需要先判断客户浏览器时候支持GZip自动解压，如果支持，则进行GZIP压缩，否则不压缩。判断的依据是浏览器提供的Header信息，代码如下：

GZipFilter.java

 package com.rom.util;

 import java.io.IOException;

 import javax.servlet.Filter;

 import javax.servlet.FilterChain;

 import javax.servlet.FilterConfig;

 import javax.servlet.ServletException;

 import javax.servlet.ServletRequest;

 import javax.servlet.ServletResponse;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 /**

  * Servlet Filter implementation class GzipFilter

  */

 public class GzipFilter implements Filter {

     /**

      * Default constructor.

      */

     public GzipFilter() {

         // TODO Auto-generated constructor stub

     }

     /**

      * @see Filter#destroy()

      */

     public void destroy() {

         // TODO Auto-generated method stub

     }

     /**

      * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)

      */

     public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) {

         // TODO Auto-generated method stub

         // place your code here

         System.out.println("压缩的");

         // TODO Auto-generated method stub

         HttpServletRequest request = (HttpServletRequest)req;

         HttpServletResponse response =(HttpServletResponse)res; 

         String acceptEncoding =request.getHeader("Accept-Encoding");

         //支持的编码方式 

         try {

             if(acceptEncoding != null && acceptEncoding.toLowerCase().indexOf("gzip") != -1){ 

                 System.out.println("执行压缩的方法");

                 //如果客户浏览器支持GZIP格式，则使用GZIP压缩数据

                 GZipResponseWrapper gzipRes = new GZipResponseWrapper(response); 

                 chain.doFilter(request, gzipRes);//doFilter,使用自定义的response

                 gzipRes.finishResponse();//输出压缩数据 

             }else{

                 System.out.println("没有压缩");

                 chain.doFilter(request, response);//否则不压缩

             }

 //          chain.doFilter(request, response);

         } catch (IOException e) {

             e.printStackTrace();

         } catch (ServletException e) {

             e.printStackTrace();

         }

     }

     /**

      * @see Filter#init(FilterConfig)

      */

     public void init(FilterConfig fConfig) throws ServletException {

         // TODO Auto-generated method stub

     }

 }

GZipResponseWrapper为自定义的response类，内部将对输出的内容进行GZIP压缩。它集成HttpServletResponseWrapper类，也是一个“伪装”的response，不真正输出内容到客户端。

GZipResponseWrapper.java

 package com.rom.util;

 import java.io.IOException;

 import java.io.OutputStreamWriter;

 import java.io.PrintWriter;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.http.HttpServletResponse;

 import javax.servlet.http.HttpServletResponseWrapper;

 public class GZipResponseWrapper extends HttpServletResponseWrapper {

      // 默认的 response

     private HttpServletResponse response; 

     // 自定义的 outputStream, 执行close()的时候对数据压缩，并输出

     private GZipOutputStream gzipOutputStream; 

     // 自定义 printWriter，将内容输出到 GZipOutputStream 中

     private PrintWriter writer; 

     public GZipResponseWrapper(HttpServletResponse response) throws IOException {

         super(response);

         this.response = response;

     } 

     public ServletOutputStream getOutputStream() throws IOException {

         if (gzipOutputStream == null)

             gzipOutputStream = new GZipOutputStream(response);

         return gzipOutputStream;

     } 

     public PrintWriter getWriter() throws IOException {

         if (writer == null)

             writer = new PrintWriter(new OutputStreamWriter(

                     new GZipOutputStream(response), "UTF-8"));

         return writer;

     } 

     // 压缩后数据长度会发生变化 因此将该方法内容置空

     public void setContentLength(int contentLength) {

     } 

     public void flushBuffer() throws IOException {

         gzipOutputStream.flush();

     } 

     public void finishResponse() throws IOException {

         if (gzipOutputStream != null)

             gzipOutputStream.close();

         if (writer != null)

             writer.close();

     }

 }

getWriter()与getOutputStream()都使用了GZipOutputStream类。这是自定义的一个ServletOutputStream类，它先将数据缓存起来，然后使用JDK自带的GZIP压缩类将数据压缩，并输出到客户端浏览器。GZIP数据压缩与输出都在该类里实现的。

GZipOutputStream.java

 package com.rom.util;

 import java.io.ByteArrayOutputStream;

 import java.io.IOException;

 import java.util.zip.GZIPOutputStream;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.http.HttpServletResponse;

 public class GZipOutputStream extends ServletOutputStream {

      private HttpServletResponse response; 

         private GZIPOutputStream gzipOutputStream; 

         private ByteArrayOutputStream byteArrayOutputStream; 

         public GZipOutputStream(HttpServletResponse response) throws IOException {

             this.response = response;

             byteArrayOutputStream = new ByteArrayOutputStream();

             gzipOutputStream = new GZIPOutputStream(byteArrayOutputStream);

         } 

         public void write(int b) throws IOException {

             gzipOutputStream.write(b);

         } 

         public void close() throws IOException { 

             gzipOutputStream.finish(); 

             byte[] content = byteArrayOutputStream.toByteArray(); 

             response.addHeader("Content-Encoding", "gzip");

             response.addHeader("Content-Length", Integer.toString(content.length)); 

             ServletOutputStream out = response.getOutputStream();

             out.write(content);

             out.close();

         } 

         public void flush() throws IOException {

             gzipOutputStream.flush();

         } 

         public void write(byte[] b, int off, int len) throws IOException {

             gzipOutputStream.write(b, off, len);

         } 

         public void write(byte[] b) throws IOException {

             gzipOutputStream.write(b);

         } 

 }

添加xml配置文件

  <filter>

   <display-name>GzipFilter</display-name>

   <filter-name>GzipFilter</filter-name>

   <filter-class>com.rom.util.GzipFilter</filter-class>

 </filter>

 <filter-mapping>

   <filter-name>GzipFilter</filter-name>

   <url-pattern>/*</url-pattern>

 </filter-mapping>

巴特西

Gzip压缩优化网站

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