tomcat接口调用时延开关

　　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 &quot;%r&quot; %s %b" />

      </Host>

　　2、这时localhost_access_log最后一个字段是文件大小：

10.111.11.179 - - [12/Mar/2018:10:04:47 +0800] "POST /wlf.hello/getHelloWorld 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 &quot;%r&quot; %s %b %D" />

　　4、重新打开localhost_access_log，加上了时延大小，单位是毫秒：

10.111.11.179 - - [21/May/2018:14:12:22 +0800] "POST /wlf.hello/getHelloWorld HTTP/1.1" 200 2519 62
10.111.11.179 - - [21/May/2018:14:12:22 +0800] "POST /wlf.hello/getHelloWorld HTTP/1.1" 200 589 72
10.111.11.179 - - [21/May/2018:14:12:23 +0800] "POST /wlf.hello/getHelloWorld HTTP/1.1" 200 2096 47