获取程序启动的所有线程的状态，不包括系统线程

代码段：

import java.util.Set;

public class ThreadStatus {
    public static void main(String args[]) throws Exception {
        for (int i = 0; i < 5; i++){
            Thread t = new Thread(new MyThread());
            t.setName("MyThread:" + i);
            t.start();
        }
        int threadCount = 0;
        Set<Thread> threadSet = Thread.getAllStackTraces().keySet();
        for (Thread t : threadSet) {
            if (t.getThreadGroup() == Thread.currentThread().getThreadGroup()) {
                System.out.println("Thread :" + t + ":" + "state:" + t.getState());
                ++threadCount;
            }
        }
        System.out.println("Thread count started by Main thread:" + threadCount);
    }
}

class MyThread implements Runnable {
    public void run() {
        try {
            Thread.sleep(2000);
        } catch(Exception err) {
            err.printStackTrace();
        }
    }
}

输出：

Thread :Thread[MyThread:1,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:3,5,main]:state:TIMED_WAITING
Thread :Thread[main,5,main]:state:RUNNABLE
Thread :Thread[MyThread:4,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:0,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:2,5,main]:state:TIMED_WAITING
Thread count started by Main thread:6

说明：

Thread.getAllStackTraces().keySet() 返回所有 Threads，包括应用程序线程和系统线程。如果你只对应用程序启动的线程状态感兴趣，请通过检查特定线程的线程组与主程序线程来迭代 Thread 集。

如果没有上面的 ThreadGroup 条件，程序将返回以下系统线程的状态：

Reference Handler
Signal Dispatcher
Attach Listener
Finalizer