How to set the -Xmx when start running a jar file?

Question

As we know that we can set -Xmx1024M in window->preferences->java->installed jres->edit->default vm arguments in eclipse. But when I package this project into a runnable jar file, how can I set the -Xmx1024M when running the jar via java -jar A.jar?

Thanks a lot!

Answer 1

Unfortunately, existing answers are wrong in one crucial point.

-Xmx must be passed to the Java runtime environment, not to the executed jar.

Wrong:

java -jar JavaApplication.jar -Xmx1024m  

Correct:

java -Xmx1024m -jar JavaApplication.jar  

More specifically, the java launcher needs to be used as follows:

java [options] -jar file.jar [arguments]

• [options] are passed to the Java runtime environment
• [arguments] are passed to the main function

The -Xmx parameter belongs to the (nonstandard) JVM options, and--being an option--needs to be listed before -jar (or at least before file.jar). The JVM will not recognize an -Xmx argument passed to the main function as proposed in other answers.

Answer 2

Three methods:

• Command Line:
  • Instruct your users to run your application using "java -jar SampleJavaApp.jar -Xmx1024m"
• Java Control Panel:
  • Instruct your users to dedicate more memory to java by default: Win7 guide
• Restart your jar with the appropriate Xmx value.

The last option is "evil" but doesn't require any extra effort from your users. Here's a sample block of code:

public static void main(String[] args) throws IOException, URISyntaxException {     String currentPath=SampleJavaApp.class           .getProtectionDomain()           .getCodeSource().getLocation()           .toURI().getPath()           .replace('/', File.separator.charAt(0)).substring(1);     if(args.length==0 && Runtime.getRuntime().maxMemory()/1024/1024<980) {         Runtime.getRuntime().exec("java -Xmx1024m -jar "+currentPath+" restart");         return;     } }