Tomcat 配置gzip无效

来源：互联网发布：淘宝怎么买弹簧刀编辑：程序博客网时间：2024/06/08 14:49

gzip的详细配置请点击笔记：《tomcat的gzip压缩配置及优化效果对比》

提升Tomcat性能方法有很多种，使用NIO Connector和启用gzip压缩是其中两种。

NIO：Java New IO，使用了多路复用的技术，无疑要比普通的IO socket要高效。

gzip：对需要传输到前台的内容首先在内存中进行gzip压缩，这样可以大大的减少网络带宽占用。前提是前台的Accept-Encoding允许gzip。

但是，当同时配置了这两个时，会发现大于48KB的文件并没有进行压缩。

经查Tomcat源码，发现org.apache.catalina.servlets.DefaultServlet中：

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/**
     * Check if sendfile can be used. 
     */ 
    protectedboolean checkSendfile(HttpServletRequest request,  
                                  HttpServletResponse response,  
                                  CacheEntry entry,  
                                  longlength, Range range) {  
        if((sendfileSize > 0) 
            && (entry.resource != null) 
            && ((length > sendfileSize) || (entry.resource.getContent() == null)) 
            && (entry.attributes.getCanonicalPath() != null) 
            && (Boolean.TRUE == request.getAttribute("org.apache.tomcat.sendfile.support")) 
            && (request.getClass().getName().equals("org.apache.catalina.connector.RequestFacade")) 
            && (response.getClass().getName().equals("org.apache.catalina.connector.ResponseFacade"))) {  
            request.setAttribute("org.apache.tomcat.sendfile.filename", entry.attributes.getCanonicalPath());  
            if(range == null) {  
                request.setAttribute("org.apache.tomcat.sendfile.start",newLong(0L));  
                request.setAttribute("org.apache.tomcat.sendfile.end",newLong(length));  
            }else{  
                request.setAttribute("org.apache.tomcat.sendfile.start",newLong(range.start));  
                request.setAttribute("org.apache.tomcat.sendfile.end",newLong(range.end + 1)); 
            } 
            returntrue; 
        }else{  
            returnfalse; 
        } 
    }

此处的sendfileSize = 48*1024，默认值为48KB，可以发现，当文件大小大于48KB时，Tomcat并未马上将内容写回到output中，而是把文件的路径记录下来。

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/**
     * Serve the specified resource, optionally including the data content. 
     *
     * @param request The servlet request we are processing 
     * @param response The servlet response we are creating 
     * @param content Should the content be included? 
     *
     * @exception IOException if an input/output error occurs 
     * @exception ServletException if a servlet-specified error occurs 
     */ 
    protectedvoid serveResource(HttpServletRequest request,  
                                 HttpServletResponse response,  
                                 booleancontent)  
        throwsIOException, ServletException {  
   
            ...... 
   
            // Copy the input stream to our output stream (if requested)  
            if(content) {  
                try{  
                    response.setBufferSize(output); 
                }catch(IllegalStateException e) {  
                    // Silent catch  
                } 
                if(ostream != null) {  
                    if(!checkSendfile(request, response, cacheEntry, contentLength, null)) 
                        copy(cacheEntry, renderResult, ostream);  
                }else{  
                    copy(cacheEntry, renderResult, writer);  
                } 
            } 
               
            ...... 
   
    }

并在Http11Processor的process方法的最后一部分，把文件内容以FileChannel的形式写回到前台，不需要先把文件内容先读到用户内存->压缩->写回socket内核内存。

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/**
     * Process pipelined HTTP requests using the specified input and output 
     * streams. 
     *
     * @throws IOException error during an I/O operation 
     */ 
    publicSocketState process(NioChannel socket)  
        throwsIOException {  
           
         ...... 
            // Do sendfile as needed: add socket to sendfile and end  
            if(sendfileData != null&& !error) {  
                KeyAttachment ka = (KeyAttachment)socket.getAttachment(false); 
                ka.setSendfileData(sendfileData); 
                sendfileData.keepAlive = keepAlive;  
                SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());  
                //do the first write on this thread, might as well  
                openSocket = socket.getPoller().processSendfile(key,ka,true,true); 
                break; 
            } 
        ...... 
   
    }

这种NIO底层读写channel的形式避免了读取到用户内存的开销，也可以提升性能。

目前，尚不清楚使用NIO快，还是gzip较快，有待测试。

如果在使用NIO的同时还一定要用gzip，可以关闭NIO Connector的useSendFile选项。

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<Connector port="8080"protocol="org.apache.coyote.http11.Http11NioProtocol" 
               connectionTimeout="20000"  
               redirectPort="8443" 
                useSendfile="false" 
                compression="on"  
                compressionMinSize="2048"  
                noCompressionUserAgents="gozilla, traviata"  
                compressableMimeType="text/html,text/xml,text/javascript"/>

参考地址：http://tomcat.apache.org/tomcat-6.0-doc/config/http.html

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