项目中有些页面时延不稳定，需要看每次接口调用时延，怎么看，有两种方法：一种是直接去catalina.out日志中看，一种是直接去localhost_access_log日志中看，第一种需要在代码中实现时延的计算，第二种方法只需在server.xml中加一个简单的配置。这里只说第二种：
1、打开tomcat下conf/server.xml，先看Host节点配置：
<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true">
<!-- SingleSignOn valve, share authentication between web applications
Documentation at: /docs/config/valve.html -->
<!--
<Valve className="org.apache.catalina.authenticator.SingleSignOn" />
-->
<!-- Access log processes all example.
Documentation at: /docs/config/valve.html
Note: The pattern used is equivalent to using pattern="common" -->
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
prefix="localhost_access_log" suffix=".txt"
pattern="%h %l %u %t "%r" %s %b" />
</Host>
2、这时localhost_access_log最后一个是文件大小：
10.73.154.72 - - [12/Mar/2018:10:04:47 +0800] "POST /ms.sns.snsService/rewardHis HTTP/1.1" 200 133
3、在conf/server.xml的Host节点中Value节点最后的pattern参数中添加% D
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
prefix="localhost_access_log" suffix=".txt"
pattern="%h %l %u %t "%r" %s %b %D" />
4、重新打开localhost_access_log，加上了时延大小，单位是毫秒：
10.125.40.179 - - [21/May/2018:14:12:22 +0800] "POST /ms.bkticket.myBookTicketService/getBookTicketRechargeList HTTP/1.1" 200 2519 62 10.125.40.179 - - [21/May/2018:14:12:22 +0800] "POST /ms.bkticket.myBookTicketService/getBookTicketRemainBalance HTTP/1.1" 200 589 72 10.125.40.179 - - [21/May/2018:14:12:23 +0800] "POST /ms.bkticket.myBookTicketService/getBookTicketRechargeList HTTP/1.1" 200 2096 47