Tomcat 配置gzip无效
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.
*/
protected
boolean
checkSendfile(HttpServletRequest request,
HttpServletResponse response,
CacheEntry entry,
long
length, 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"
,
new
Long(0L));
request.setAttribute(
"org.apache.tomcat.sendfile.end"
,
new
Long(length));
}
else
{
request.setAttribute(
"org.apache.tomcat.sendfile.start"
,
new
Long(range.start));
request.setAttribute(
"org.apache.tomcat.sendfile.end"
,
new
Long(range.end +
1
));
}
return
true
;
}
else
{
return
false
;
}
}
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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
*/
protected
void
serveResource(HttpServletRequest request,
HttpServletResponse response,
boolean
content)
throws
IOException, 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);
}
}
......
}
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/**
* Process pipelined HTTP requests using the specified input and output
* streams.
*
* @throws IOException error during an I/O operation
*/
public
SocketState process(NioChannel socket)
throws
IOException {
......
// 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
;
}
......
}
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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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connectionTimeout=
"20000"
redirectPort=
"8443"
useSendfile=
"false"
compression=
"on"
compressionMinSize=
"2048"
noCompressionUserAgents=
"gozilla, traviata"
compressableMimeType=
"text/html,text/xml,text/javascript"
/>
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参考地址：http://tomcat.apache.org/tomcat-6.0-doc/config/http.html