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>