DigitLiao's Notebook

大部分的瀏覽器都有支援Gzip的壓縮格式，因此在將內容傳給Client時可以先把內容以Gzip的方式壓縮來結省傳輸量，
如果您是租用虛擬主機的話，主機商大部份都是以傳輸流量來計費的，若您的網站在一個月內超過1G或其他規定的限制量
就需要多繳額外的費用了，因此這隻程式可以幫您多省一些頻寬。

如果大部分都文字的網頁經過Gzip壓縮，檔案大小可以壓到到原本的20%。



package com.jsptw.filter;
import java.io.*;
import java.util.zip.GZIPOutputStream;
import javax.servlet.*;
import javax.servlet.http.*;
public class GZIPEncodeFilter 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();       
     }  
   }
}