gzip是http協議中使用的一種加密算法,客戶端向web服務器端發出了請求後，通常情況下服務器端會將頁面文件和其他資源，返回到客戶端，客戶端加載後渲染呈現，這種情況文件一般都比較大，如果開啓Gzip ，那麼服務器端響應後，會將頁面，JS,CSS等文本文件或者其他文件通過高壓縮算法將其壓縮，然後傳輸到客戶端，由客戶端的瀏覽器負責解壓縮與呈現。通常能節省40%以上的流量（一般都有60%左右），一些PHP，JSP文件也能夠進行壓縮。
實 現：
Tomcat 開啓Gzip ：
1.找到Tomcat 目錄下的conf下的server.xml，並找到如下信息
將它改成如下的形式（其實在上面代碼的下面已經有了，將他們打開而已。）：
這樣，就能夠對html和xml進行壓縮了，如果要壓縮css 和 js，那麼需要將
compressableMimeType=”text/html,text/xml”加入css和js：
你甚至可以壓縮圖片：
compressableMimeType=”text/html,text/xml”加入css和js：
開啓後重啓Tomcat ，通過瀏覽器查看headers信息就能看到是否開啓（firebug中有），如果開啓了，那麼transfer-encoding就會是Gzip，否則就是chunked。
在代碼級別完成web應用的gzip壓縮的開啓：
1.Wrapper 用來包裝HttpServletResponse 對象
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.過濾器
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() {
}
/**
* 判斷瀏覽器是否支持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,當我們訪問應用中以.do結尾的資源的使用,服務器端就開啓http gzip壓縮,將壓縮後的信息通過http 協議傳遞給瀏覽器.
<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>