列出JVM中所有的線程組和線程

這個類包含一個有用的靜態方法列出所有在JVM中的線程和線程組。它也有一個簡單的main（）方法，以便它可以作為一個獨立的程序運行。

import java.awt.BorderLayout;
import java.io.PrintWriter;
import java.io.StringWriter;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
/**

This class contains a useful static method for listing all threads and
threadgroups in the VM. It also has a simple main() method so it can be run
as a standalone program.
/
public class ThreadLister {
/** Display information about a thread. /
private static void printThreadInfo(PrintWriter out, Thread t, String indent) {
 if (t == null)
   return;
 out.println(indent + "Thread: " + t.getName() + "  Priority: " + t.getPriority()

 + (t.isDaemon() ? " Daemon" : "") + (t.isAlive() ? "" : " Not Alive"));

}
/* Display info about a thread group and its threads and groups /
private static void printGroupInfo(PrintWriter out, ThreadGroup g, String indent) {
 if (g == null)
   return;
 int num_threads = g.activeCount();
 int num_groups = g.activeGroupCount();
 Thread[] threads = new Thread[num_threads];
 ThreadGroup[] groups = new ThreadGroup[num_groups];
g.enumerate(threads, false);
 g.enumerate(groups, false);
out.println(indent + "Thread Group: " + g.getName() + "  Max Priority: " + g.getMaxPriority()

 + (g.isDaemon() ? " Daemon" : ""));


for (int i = 0; i < num_threads; i++)
   printThreadInfo(out, threads[i], indent + "    ");
 for (int i = 0; i < num_groups; i++)
   printGroupInfo(out, groups[i], indent + "    ");
}
/* Find the root thread group and list it recursively /
public static void listAllThreads(PrintWriter out) {
 ThreadGroup current_thread_group;
 ThreadGroup root_thread_group;
 ThreadGroup parent;
// Get the current thread group
 current_thread_group = Thread.currentThread().getThreadGroup();
// Now go find the root thread group
 root_thread_group = current_thread_group;
 parent = root_thread_group.getParent();
 while (parent != null) {
   root_thread_group = parent;
   parent = parent.getParent();
 }
// And list it, recursively
 printGroupInfo(out, root_thread_group, "");
}
/**

The main() method create a simple graphical user interface to display the
threads in. This allows us to see the "event dispatch thread" used by AWT
and Swing.
*/
public static void main(String[] args) {
// Create a simple Swing GUI
JFrame frame = new JFrame("ThreadLister Demo");
JTextArea textarea = new JTextArea();
frame.getContentPane().add(new JScrollPane(textarea), BorderLayout.CENTER);
frame.setSize(500, 400);
frame.setVisible(true);
// Get the threadlisting as a string using a StringWriter stream
StringWriter sout = new StringWriter(); // To capture the listing
PrintWriter out = new PrintWriter(sout);
ThreadLister.listAllThreads(out); // List threads to stream
out.close();
String threadListing = sout.toString(); // Get listing as a string
// Finally, display the thread listing in the GUI
textarea.setText(threadListing);
}
}</pre>