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>