把一个AccessLogValve在Host或Context元素如：

<Host name="www.mysite.com" appBase="..." >

    <Valve className="org.apache.catalina.valves.AccessLogValve"
     directory="logs" prefix="mysitelog." suffix=".txt" 
     pattern="..." resolveHosts="false" />

</Host>

该pattern属性可以采用两个速记值之一（ common ， combined
）或使用多个常量和替换字符串的自定义模式。让我引用Tomcat文档：

https://tomcat.apache.org/tomcat-8.0-doc/config/valve.html#Access_Log_Valve

pattern属性的值由文字字符串组成，并以“％”字符作为前缀的模式标识符组合在一起，以替换为来自当前请求和响应的相应变量值。支持以下模式代码：

>     %a - Remote IP address
>     %A - Local IP address
>     %b - Bytes sent, excluding HTTP headers, or '-' if zero
>     %B - Bytes sent, excluding HTTP headers
>     %h - Remote host name (or IP address if enableLookups for the connector
> is false)
>     %H - Request protocol
>     %l - Remote logical username from identd (always returns '-')
>     %m - Request method (GET, POST, etc.)
>     %p - Local port on which this request was received. See also %{xxx}p
> below.
>     %q - Query string (prepended with a '?' if it exists)
>     %r - First line of the request (method and request URI)
>     %s - HTTP status code of the response
>     %S - User session ID
>     %t - Date and time, in Common Log Format
>     %u - Remote user that was authenticated (if any), else '-'
>     %U - Requested URL path
>     %v - Local server name
>     %D - Time taken to process the request, in millis
>     %T - Time taken to process the request, in seconds
>     %F - Time taken to commit the response, in millis
>     %I - Current request thread name (can compare later with stacktraces)

还支持编写信息传入或传出的标头，cookie，会话或请求属性以及特殊的时间戳格式。它是根据Apache HTTP Server日志配置语法建模的。它们每个都可以使用不同的xxx键多次使用：

>     %{xxx}i write value of incoming header with name xxx
>     %{xxx}o write value of outgoing header with name xxx
>     %{xxx}c write value of cookie with name xxx
>     %{xxx}r write value of ServletRequest attribute with name xxx
>     %{xxx}s write value of HttpSession attribute with name xxx
>     %{xxx}p write local (server) port (xxx==local) or remote (client) port
> (xxx=remote)
>     %{xxx}t write timestamp at the end of the request formatted using the
> enhanced SimpleDateFormat pattern xxx

如您所见，可以使用很多字段，但是如果仍然需要更多字段，则必须编写自己的AccessLogValve实现。