How do I set maximal jvm-memory (XMX) for a jar-file

Question

How do I set the maximal jvm-memory without adding an extra batch-script to my Programm. Answer is provided below.

Answer 1

My approach is to add a parameter to my program which i set when the jvm is configured properly.

Like this:

public static void main(final String args[]) {
        if ((args.length != 0) && args[0].equals("xmx_set"))
            runClient();
        else {
            try {
                Runtime.getRuntime().exec("java -Xmx256M -jar client.jar xmx_set");
            } catch (final IOException e) {
                e.printStackTrace();
            }
        }
    }

Answer 2

It's a good question, but your implmenetation assumes a lot. I presume you have to document the name of your jar for your users to invoke "java -jar xyz.jar" on so can you also include in the documentation that "-Xmx256M" is required?

You may have more luck using a java launcher, such as this one for Windows, where you put the launcher config (path, max memory etc.) in a separate file. For cross platform, there's LaunchAnywhere, and others, which function similarly. See http://stackoverflow.com/questions/147181/how-can-i-convert-my-java-program-to-an-exe-file

To improve upon your existing scheme:

• use the java.home system property to resolve the location of the JDK/JRE
• use the java.class.path to set up the class path, and similarly for java.library.path if your application requires native code.
• pass command arguments passed to your main method to the spanwed process

But still, this seems to be a lot of effort that at best represents a leaky abstraction, when instead simple and clear documentation would suffice.