If you ever need to create log files that are automatically prefixed by the process id of the native OS-level JVM process (or any other unique identifier for the VM process), it can be difficult, due to the lack of a straightforward mechanism in Java for obtaining the process handle or id. However, you can work around the limitation like this (JDK 1.5+ only):
import org.apache.log4j.FileAppender;
public class PidPrefixFileAppender extends FileAppender {
@Override
public void setFile(String file) {
RuntimeMXBean rt = ManagementFactory.getRuntimeMXBean();
super.setFile(rt.getName() + "-" + file);
}
}
This will automatically prefix any log files created via this appender, for example:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{DATE} %-5p %-15c (%F:%M:%L) - %m%n"/>
</layout>
</appender>
<appender name="CacheLoadCsvAppender" class="co.uk.researchkitchen.PidPrefixFileAppender">
<param name="File" value="cacheload.log"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%m%n"/>
</layout>
</appender>
<category name="cacheLoadLogger" additivity="false">
<priority value="info"/>
<appender-ref ref="CacheLoadCsvAppender"/>
</category>
<root>
<priority value="info" />
</root>
</log4j:configuration>
Will produce log files in the format processid@machine_id-cacheload.log.
