Is there a way to get user's UID on Linux machine using java?

you can execute id command and read result.

for example:

$ id -u jigar

output:

1000

you can execute command by

try {
    String userName = System.getProperty("user.name");
    String command = "id -u "+userName;
    Process child = Runtime.getRuntime().exec(command);

    // Get the input stream and read from it
    InputStream in = child.getInputStream();
    int c;
    while ((c = in.read()) != -1) {
        process((char)c);
    }
    in.close();
} catch (IOException e) {
}

source

There is actually an api for this. There is no need to call a shell command or use JNI, just

def uid = new com.sun.security.auth.module.UnixSystem().getUid()

If you can influence how the Java VM is started, you could handover the uid as a user property:

java -Duserid=$(id -u) CoolApp

In your CoolApp, you could simply fetch the ID with:

System.getProperty("userid");

Regards,

Martin.