Can I invoke a main method passing jvm parameter?

Question

My intent is that I want to debug something of hadoop. The command to run the hadoop program is :

bin/hadoop jar path/to/hadoop-mapreduce-examples-2.2.0.jar wordcount /wordcount /output

And this command will call the RunJar.java 's main() method . I could pass jvm parameter to RunJar.java 's main() method by add these in hadoop-env.sh :

HADOOP_OPTS="$HADOOP_OPTS -Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=9000"

But the code inside RunJar.java 's main() is :

ClassLoader loader =
  new URLClassLoader(classPath.toArray(new URL[0]));
Class<?> mainClass = Class.forName(mainClassName, true, loader);
Method main = mainClass.getMethod("main", new Class[] {
  Array.newInstance(String.class, 0).getClass()
});
main.invoke(null, new Object[] { newArgs });

Can I pass some jvm parameter ( -Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=8999 ) to this invoke method

main.invoke(null, new Object[] { newArgs });

So that I could debug the main method invoked by RunJar.java in remote way

Answer 1

No, the JVM is already started.

The only way is if you run your JAR by starting a new JVM using Runtime.getRuntime().exec() or ProcessBuilder and Process classes.

This would probably do the trick, and you woudn't need to pass the arguments since you can actually call the script:

Runtime.getRuntime().exec(
        "bin/hadoop jar path/to/hadoop-mapreduce-examples-2.2.0.jar " +
        "wordcount /wordcount /output");