Tomcat7启用gzip压缩

背景：HTTP 压缩可以大大提高浏览网站的速度，它的原理是，在客户端请求网页后，从服务器端将网页文件压缩，再下载到客户端，由客户端的浏览器负责解压缩并浏览。相对于普通的浏览过程HTML ,CSS,Javascript , Text ，它可以节省40%左右的流量。更为重要的是，它可以对动态生成的，包括CGI、PHP , JSP , ASP , Servlet,SHTML等输出的网页也能进行压缩，压缩效率惊人。

第一步:修改$tomcat_home$/conf/server.xml
将
<Connector connectionTimeout="20000" port="8080" protocol="HTTP/1.1" redirectPort="8443"/>
修改为
<Connector connectionTimeout="20000" port="8080" protocol="HTTP/1.1" 　　redirectPort="8443"　        
　　　　　compression="on"
         compressionMinSize="2048"
         noCompressionUserAgents="gozilla, traviata"
         compressableMimeType="text/html,text/xml,text/plain,text/css,
         text/javascript,text/json,application/x-javascript,
         application/javascript,application/json"/>
注意要添加application/javascript,tomcat5用的可能是text/javascript,但tomcat7用的是application/javascript

第二步:用浏览器访问你重新部署的程序，打开开发者工具，进入Network面板，刷新页面，然后选择一个js文件点击，查看　Headers下面的Response Headers，里面会标明Encoding为gzip,那么恭喜你成功了。

以上是服务器自动帮你压缩文件，但如果文件比较大，你希望提前压缩后，到时候服务器自动读取你压缩的gzip文件而不是由服务器来压缩，怎么做呢?
第一步:实现filter类，让filter类来读取你压缩的gzip文件

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.logging.Logger;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
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 {

	private ServletContext ctx;
	private Logger logger = Logger.getLogger(GzipFilter.class.getName());
	private String contextPath;

	@Override
	public void destroy() {

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse res = (HttpServletResponse) response;
		String uri = req.getRequestURI();
		String accept = req.getHeader("Accept-Encoding");
		InputStream in = null;
		contextPath = ctx.getContextPath();
		uri = uri.substring(contextPath.length());
		if (accept != null && accept.contains("gzip") && (in = ctx.getResourceAsStream(uri + ".gz")) != null) {
			logger.info("start getting gzip file "+uri);
			ByteArrayOutputStream bout = new ByteArrayOutputStream();
			byte[] b = new byte[1024 * 8];
			int read = 0;
			while ((read = in.read(b)) >= 0) {
				bout.write(b, 0, read);
			}
			in.close();

			res.setHeader("Content-Encoding", "gzip");
			res.setContentType("application/javascript;charset=UTF-8");
			res.setContentLength(bout.size());

			ServletOutputStream out = res.getOutputStream();
			out.write(bout.toByteArray());
			out.flush();
			logger.info("finish getting gzip file "+uri);
			return;
		} else {   
			chain.doFilter(request, response);
		}
	}

	@Override
	public void init(FilterConfig config) throws ServletException {
		ctx = config.getServletContext();
	}

}

第二步:配置web.xml
添加如下片段即可

	<!-- read the precompressed gzip js file-->
	<filter>
		<filter-name>gzip</filter-name>
		<filter-class>GzipFilter</filter-class>
	</filter>
 
	<filter-mapping>
		<filter-name>gzip</filter-name>
		<url-pattern>*.js</url-pattern>
	</filter-mapping>

第三步:压缩你的js文件，比如a.js为a.js.gzip文件
第四步:用chrome验证是否成功