Log4j Rewrite Appender

PropertyRewritePolicy

<appender name="stdoutaddprops" class="org.apache.log4j.rewrite.RewriteAppender">
  <appender-ref ref="stdout" />
    <rewritePolicy class="org.apache.log4j.rewrite.PropertyRewritePolicy">
      <param name="properties" value="p1=Hello,p2=World,x1=3.1415,username=${user.name}"/>
    </rewritePolicy>
</appender>