使用gzip优化web应用(filter实现)

相关知识：

　　gzip是http协议中使用的一种加密算法,客户端向web服务器端发出了请求后，通常情况下服务器端会将页面文件和其他资源，返回到客户端，客户端加载后渲染呈现，这种情况文件一般都比较大，如果开启Gzip ，那么服务器端响应后，会将页面，JS,CSS等文本文件或者其他文件通过高压缩算法将其压缩，然后传输到客户端，由客户端的浏览器负责解压缩与呈现。通常能节省40%以上的流量（一般都有60%左右），一些PHP，JSP文件也能够进行压缩。

实      现：　　

Tomcat 开启Gzip ：

1.找到Tomcat 目录下的conf下的server.xml，并找到如下信息

Connector port="8080" maxHttpHeaderSize="8192" maxThreads="150" minSpareThreads="25" maxSpareThreads="75" enableLookups="false" redirectPort="8443" acceptCount="100" connectionTimeout="20000" disableUploadTimeout="true"
将它改成如下的形式（其实在上面代码的下面已经有了，将他们打开而已。）：

<!-- Define a non-SSL HTTP/1.1 Connector on port 8080 --> <Connector port="8080" maxHttpHeaderSize="8192" maxThreads="150" minSpareThreads="25" maxSpareThreads="75" enableLookups="false" redirectPort="8443" acceptCount="100" connectionTimeout="20000" disableUploadTimeout="true" compression="on" compressionMinSize="2048" noCompressionUserAgents="gozilla, traviata" compressableMimeType="text/html,text/xml" >
这样，就能够对html和xml进行压缩了，如果要压缩css 和 js，那么需要将

compressableMimeType=”text/html,text/xml”加入css和js：

<Connector port="8080" ......... compressableMimeType="text/html,text/xml,text/css,text/javascript" >
你甚至可以压缩图片：

compressableMimeType=”text/html,text/xml”加入css和js：

<Connector port="8080" ......... compressableMimeType="text/html,text/xml,text/css,text/javascript,image/gif,image/jpg" >
开启后重启Tomcat ，通过浏览器查看headers信息就能看到是否开启（firebug中有），如果开启了，那么transfer-encoding就会是Gzip，否则就是chunked。



在代码级别完成web应用的gzip压缩的开启：



1.Wrapper  用来包装HttpServletResponse 对象

Java代码 public class Wrapper extends HttpServletResponseWrapper
{
public static final int OT_NONE = 0, OT_WRITER = 1, OT_STREAM = 2;
private int outputType = OT_NONE;
private ServletOutputStream output = null;
private PrintWriter writer = null;
private ByteArrayOutputStream buffer = null;
public Wrapper(HttpServletResponse resp) throws IOException {
super(resp);
buffer = new ByteArrayOutputStream();
}
public PrintWriter getWriter() throws IOException {
if(outputType==OT_STREAM)
throw new IllegalStateException();
else if(outputType==OT_WRITER)
return writer;
else {
outputType = OT_WRITER;
writer = new PrintWriter(new OutputStreamWriter(buffer, getCharacterEncoding()));
return writer;
}
}
public ServletOutputStream getOutputStream() throws IOException {
if(outputType==OT_WRITER)
throw new IllegalStateException();
else if(outputType==OT_STREAM)
return output;
else {
outputType = OT_STREAM;
output = new WrappedOutputStream(buffer);
return output;
}
}
public void flushBuffer() throws IOException {
if(outputType==OT_WRITER)
writer.flush();
if(outputType==OT_STREAM)
output.flush();
}
public void reset() {
outputType = OT_NONE;
buffer.reset();
}
public byte[] getResponseData() throws IOException {
flushBuffer();
return buffer.toByteArray();

}
class WrappedOutputStream extends ServletOutputStream {
private ByteArrayOutputStream buffer;
public WrappedOutputStream(ByteArrayOutputStream buffer) {
this.buffer = buffer;
}
public void write(int b) throws IOException {
buffer.write(b);
}
public byte[] toByteArray() {
return buffer.toByteArray();
}
}
}
package com.shop.gzip;

import java.io.ByteArrayOutputStream;
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 Wrapper extends HttpServletResponseWrapper {
    public static final int OT_NONE = 0, OT_WRITER = 1, OT_STREAM = 2;
    private int outputType = OT_NONE;
    private ServletOutputStream output = null;
    private PrintWriter writer = null;
    private ByteArrayOutputStream buffer = null;

    public Wrapper(HttpServletResponse resp) throws IOException {
        super(resp);
        buffer = new ByteArrayOutputStream();
    }

    public PrintWriter getWriter() throws IOException {
        if (outputType == OT_STREAM)
            throw new IllegalStateException();
        else if (outputType == OT_WRITER)
            return writer;
        else {
            outputType = OT_WRITER;
            writer = new PrintWriter(new OutputStreamWriter(buffer,
                    getCharacterEncoding()));
            return writer;
        }
    }

    public ServletOutputStream getOutputStream() throws IOException {
        if (outputType == OT_WRITER)
            throw new IllegalStateException();
        else if (outputType == OT_STREAM)
            return output;
        else {
            outputType = OT_STREAM;
            output = new WrappedOutputStream(buffer);
            return output;
        }
    }

    public void flushBuffer() throws IOException {
        if (outputType == OT_WRITER)
            writer.flush();
        if (outputType == OT_STREAM)
            output.flush();
    }

    public void reset() {
        outputType = OT_NONE;
        buffer.reset();
    }

    public byte[] getResponseData() throws IOException {
        flushBuffer();
        return buffer.toByteArray();

    }

    class WrappedOutputStream extends ServletOutputStream {
        private ByteArrayOutputStream buffer;

        public WrappedOutputStream(ByteArrayOutputStream buffer) {
            this.buffer = buffer;
        }

        public void write(int b) throws IOException {
            buffer.write(b);
        }

        public byte[] toByteArray() {
            return buffer.toByteArray();
        }
    }
}






2.过滤器



Java代码 public class GZipFilter implements Filter
{

public void destroy()
{
  // TODO Auto-generated method stub
 
}

public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain chain) throws IOException, ServletException
   {
   System.out.println("进入过滤器");
   HttpServletResponse resp = (HttpServletResponse)response;
   Wrapper wrapper = new Wrapper(resp);
   chain.doFilter(request, wrapper);
   byte[] gzipData = gzip(wrapper.getResponseData());
   resp.addHeader("Content-Encoding", "gzip");
   resp.setContentLength(gzipData.length);
   ServletOutputStream output = response.getOutputStream();
   output.write(gzipData);
   output.flush();
   }

public void init(FilterConfig arg0) throws ServletException
{
  // TODO Auto-generated method stub
 
}

private byte[] gzip(byte[] data) {
  ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240);
  GZIPOutputStream output = null;
  try {
  output = new GZIPOutputStream(byteOutput);
  output.write(data);
  }
  catch (IOException e) {}
  finally {
  try {
  output.close();
  }
  catch (IOException e) {}
  }
  return byteOutput.toByteArray();
  }

}


package com.shop.gzip;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.GZIPOutputStream;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class GZipFilter implements Filter {

    public void destroy() {
    }
      /**
       * 判断浏览器是否支持GZIP
       * @param request
       * @return
       */
      private static boolean isGZipEncoding(HttpServletRequest request){
        boolean flag=false;
        String encoding=request.getHeader("Accept-Encoding");
        if(encoding.indexOf("gzip")!=-1){
          flag=true;
        }
        return flag;
      }
     
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletResponse resp = (HttpServletResponse) response;
        HttpServletRequest req=(HttpServletRequest)request;
        if(isGZipEncoding(req)){
            Wrapper wrapper = new Wrapper(resp);
            chain.doFilter(request, wrapper);
            byte[] gzipData = gzip(wrapper.getResponseData());
            resp.addHeader("Content-Encoding", "gzip");
            resp.setContentLength(gzipData.length);
            ServletOutputStream output = response.getOutputStream();
            output.write(gzipData);
            output.flush();
        } else {
            chain.doFilter(request, response);
        }       

    }

    public void init(FilterConfig arg0) throws ServletException {

    }

    private byte[] gzip(byte[] data) {
        ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240);
        GZIPOutputStream output = null;
        try {
            output = new GZIPOutputStream(byteOutput);
            output.write(data);
        } catch (IOException e) {
        } finally {
            try {
                output.close();
            } catch (IOException e) {
            }
        }
        return byteOutput.toByteArray();
    }

}

3.在web.xml中配置 GZipFilter,当我们访问应用中以.do结尾的资源的使用,服务器端就开启http gzip压缩,将压缩后的信息通过http 协议传递给浏览器. 

  

Xml代码 <filter> 

　　<filter-name>ecsideExport</filter-name> 

　　<filter-class>com.web.servlet.GZipFilter</filter-class> 

</filter> 

<filter-mapping> 

             <filter-name>ecsideExport</filter-name> 

            <url-pattern>*.do</url-pattern> 

</filter-mapping>