$0 (Program Name) in Java? Discover main class?

Solution 1:

Try this:

    StackTraceElement[] stack = Thread.currentThread ().getStackTrace ();
    StackTraceElement main = stack[stack.length - 1];
    String mainClass = main.getClassName ();

Of course, this only works if you're running from the main thread. Unfortunately I don't think there's a system property you can query to find this out.

Edit: Pulling in @John Meagher's comment, which is a great idea:

To expand on @jodonnell you can also get all stack traces in the system using Thread.getAllStackTraces(). From this you can search all the stack traces for the "main" Thread to determine what the main class is. This will work even if your class is not running in the main thread.

Solution 2:

System.getProperty("sun.java.command")

Solution 3:

To expand on @jodonnell you can also get all stack traces in the system using Thread.getAllStackTraces(). From this you can search all the stack traces for the main Thread to determine what the main class is. This will work even if your class is not running in the main thread.

Solution 4:

This is the code I came up with when using the combined responses of jodonnell and John Meagher. It stores the main class in a static variable to reduce overhead of repeated calls:

private static Class<?> mainClass;

public static Class<?> getMainClass() {
  if (mainClass != null)
    return mainClass;

  Collection<StackTraceElement[]> stacks = Thread.getAllStackTraces().values();
  for (StackTraceElement[] currStack : stacks) {
    if (currStack.length==0)
      continue;
    StackTraceElement lastElem = currStack[currStack.length - 1];
    if (lastElem.getMethodName().equals("main")) {
      try {
        String mainClassName = lastElem.getClassName();
        mainClass = Class.forName(mainClassName);
        return mainClass;
      } catch (ClassNotFoundException e) {
        // bad class name in line containing main?! 
        // shouldn't happen
        e.printStackTrace();
      }
    }
  }
  return null;
}