GZIP压缩优化

Posted 2020-08-14 Cool咔咔

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了GZIP压缩优化相关的知识，希望对你有一定的参考价值。

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。）：

<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：

你甚至可以压缩图片：

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

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

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

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();
   }

}