Get a list of all threads currently running in Java

Question

Is there any way I can get a list of all running threads in the current JVM (including the threads not started by my class)?

Is it also possible to get the

Answer 1

Code snippet to get list of threads started by main thread:

import java.util.Set;

public class ThreadSet {
    public static void main(String args[]) throws Exception{
        Thread.currentThread().setName("ThreadSet");
        for ( int i=0; i< 3; i++){
            Thread t = new Thread(new MyThread());
            t.setName("MyThread:"+i);
            t.start();
        }
        Set threadSet = Thread.getAllStackTraces().keySet();
        for ( Thread t : threadSet){
            if ( t.getThreadGroup() == Thread.currentThread().getThreadGroup()){
                System.out.println("Thread :"+t+":"+"state:"+t.getState());
            }
        }
    }
}

class MyThread implements Runnable{
    public void run(){
        try{
            Thread.sleep(5000);
        }catch(Exception err){
            err.printStackTrace();
        }
    }
}

output:

Thread :Thread[MyThread:2,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:0,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:1,5,main]:state:TIMED_WAITING
Thread :Thread[ThreadSet,5,main]:state:RUNNABLE

If you need all threads including system threads, which have not been started by your program, remove below condition.

if ( t.getThreadGroup() == Thread.currentThread().getThreadGroup())

Now output:

Thread :Thread[MyThread:2,5,main]:state:TIMED_WAITING
Thread :Thread[Reference Handler,10,system]:state:WAITING
Thread :Thread[MyThread:1,5,main]:state:TIMED_WAITING
Thread :Thread[ThreadSet,5,main]:state:RUNNABLE
Thread :Thread[MyThread:0,5,main]:state:TIMED_WAITING
Thread :Thread[Finalizer,8,system]:state:WAITING
Thread :Thread[Signal Dispatcher,9,system]:state:RUNNABLE
Thread :Thread[Attach Listener,5,system]:state:RUNNABLE