Java – Change WebSphere’s default Java SDK from IBM’s JVM to Oracle’s

javac generally spawns a separate process which should fall underneath different process rules.

-J options are for passing args via a wrapper/launcher to the JVM, I've not seen this on Tomcat.

Find out where the -Xmx is coming from:

find /your/install/dir/with/tomcat |xargs grep '-Xmx'

Without digging into the guts of Tomcat to be sure, I think that the sequence will be something like this.

1. A new process for the JVM is launched, passing 'stdin', 'stdout' and 'stderr' file descriptors. These will typically be set up by the calling shell and passed to the JVM across the fork/exec syscalls. (Or whatever the Windows equivalent is ...) But in this case, there is some wrapper script or native application that redirects 'stdout' to "jakarta_service_xxx.log" before the JVM is launched.

2. The JVM creates some internal logging system (implemented in native code) that will be used by the GC and other JVM services for JVM logging. This will use the 'stdout' or 'stderr' file descriptors.

3. The JVM creates PrintStream(OutputStream) objects that wrap 'stdout' and 'stderr' file descriptors and sets java.lang.System.out and java.lang.System.err to these objects respectively.

4. The JVM calls the Tomcat main method to start Tomcat.

5. Tomcat opens a new FileOutputStream to "stdout_xxx.log" and uses java.lang.System.setOut() to update java.lang.System.out. If there are different "stdout_xxx.log" files for each webapp, then it is likely that Tomcat has implemented a clever output stream proxy that demuxes output to different log files based on thread groups or something ...

I suspect that the JVM logging is not using java.util.Logging ... or any Java code at all. It just looks like it is. I say this because I think the JVM would get into knots if it tried to call into Java code at certain points; for example at critical points in the GC. But I might be wrong about this ...

As to WHY this is happening, I think it is happening because it is generally a good idea to separate "System.out/err" output coming from the webapps and from the jvm / tomcat core. There are probably configuration files etc that allow you to change this ... if you want to.