Programmatically Set -X: and -XX: System Properties in JVM

Question

I know The -D properties can be set by System.setProperty() which takes the key=>value form.

But how do I set the -XX options. I'm specifically looking to set -XX:+PrintGCDetails inside main();

Answer 1

You can't change that once the JVM has started. These are not Java system properties, but parameters that govern the startup and configuration of the JVM system.

Answer 2

If you are launching a java applet you can pass them in a parameter called java_arguments.

If you are launching a JNLP program you can pass the parameters like this:

<resources>
    <jar href="MyApp.jar" />
    <java version="1.6+" initial-heap-size="5m" max-heap-size="256m" java-vm-args="-XXSomeOption" />
</resources>

You cannot change these parameters once the application is running, but you can re-launch java by looking at system properties like java.home to determine which JVM was used to launch your program.

Answer 3

The only way to set these values is to start another Java process. You can start a new process with the parameters you want and exit. You can't change the options once the process has started.