Determining location of JVM executable during runtime

Question

How does one obtain the location of the executable of the currently running JVM during runtime? I would like to instantiate another JVM as a subprocess using the ProcessBuilder class.

I am aware that there is the java.home System property, but this doesn't specify the location of the JVM executable. I understand I could do something like this to get the path:

System.getProperties().getProperty("java.home") + File.pathSeparator + "bin" + File.pathSeparator + "java"

This code isn't platform independent, because the Windows executable's name is java.exe, not java. Is there a way to get the path of the JVM executable that takes the platform's idiosyncrasies into account?

Answer 1

You could always just use os.name to check if the user is running Windows or not. That'll work on OS X, Linux and Windows at

String jvm_location;
if (System.getProperty("os.name").startsWith("Win")) {
    jvm_location = System.getProperties().getProperty("java.home") + File.separator + "bin" + File.separator + "java.exe";
} else {
    jvm_location = System.getProperties().getProperty("java.home") + File.separator + "bin" + File.separator + "java";
}

Answer 2

Yes, there is a way to get the path of the JVM executable (if it exists). Include it in the configuration of the application. There are lots of ways to do that: Command line argument -- java myApp.Main /path/to/Java; Properties -- java -Dpath.to.java=/path/to/java; etc.

If you want true platform independence, then your whole scheme is flawed because the existence of a JVM executable is not guaranteed. I could imagine a JVM with no need for a java executable.

If you want 99.99% platform independence, then I think you have the tools needed.

Answer 3

This thread has an interesting discussion of the issue covering several platforms: Finding current executable's path without /proc/self/exe

Given that discussion, it should be possible, if you really needed it, to write some JNI wrapper that #ifdef's the current platform and makes the proper native call.

If you're only on Linux the '/proc/self/exe' is a symbolic link to the actual executable being run. This has the advantage of not relying on any environment variables (i.e. PATH or JAVA_HOME). But as I said, it's definitely not platform independent.

Answer 4

You are trying to fork the entire JVM.

1. That is extremely inefficient, mainly because of the heaviness of yet another java process. If your heavily doing this, then your program is going to be really slow
2. Threads exist for this very reason

But if you really must, you can try just executing java -arguments directly, since most standard java installations put java on the cli path.