Log4J Filters

[Karthik Vijayarajan]

Hi,
I am trying to understand some Filter configurations in log4j xml. I came across this code in my application which sounds little confusing to me.

   
 
<appender name="TRACE_SPECIFIC" class="org.apache.log4j.RollingFileAppender">
<param name="file" value="C:\\Log\\Test.log"/>
   <param name="MaxFileSize" value="10000KB"/>
   <param name="MaxBackupIndex" value="10"/>
    <param name="Append" value="true" />
 <param name="Threshold" value="ALL"/>
<layout class="org.apache.log4j.PatternLayout">
 <param name="ConversionPattern"value="%d{ISO8601} %c %p :  %m %n"/>
</layout>
       
       [B]<filter class="org.apache.log4j.varia.LevelMatchFilter">
  <param name="LevelToMatch" value="TRACE"/>
  <param name="AcceptOnMatch" value="true"/>
       </filter>[/B]
 
       <filter class="org.apache.log4j.varia.DenyAllFilter"/>

If my understanding is right, the first filter LevelMatchFilter says that Log4j should log all requests that are at level TRACE and should not consult remaining filters. I cant quite get as why i need the second filter DenyAllFilter. Can you please throw some light? Thank you.

[ September 02, 2008: Message edited by: Karthik Vijayarajan ]
[ September 02, 2008: Message edited by: Karthik Vijayarajan ]

[Paul Michael]

From the docs of DenyAllFilter:

You can add this filter to the end of a filter chain to switch from the default "accept all unless instructed otherwise" filtering behaviour to a "deny all unless instructed otherwise" behaviour.

Hope this helps.

[Karthik Vijayarajan]

Thank you for the response.
I thought the first filter's[LevelMatchFilter] configuration establishes what the DenyAllFilter would do. The configuration doesnt seem to be posing any problems though. I guess since the LevelMatchFilter configuration returns "ACCEPT", the DenyAllFilter is not consulted at all. Thank you.