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ThreadLister.javaAPI DocExample3814Sat Jan 24 10:44:26 GMT 2004je3.thread

ThreadLister

public class ThreadLister extends Object
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.

Fields Summary
Constructors Summary
Methods Summary
public static voidlistAllThreads(java.io.PrintWriter out)
Find the root thread group and list it recursively

        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, "");
public static voidmain(java.lang.String[] args)
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.

	// 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);
private static voidprintGroupInfo(java.io.PrintWriter out, java.lang.ThreadGroup g, java.lang.String indent)
Display info about a thread group and its threads and groups

        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 + "    ");
private static voidprintThreadInfo(java.io.PrintWriter out, java.lang.Thread t, java.lang.String indent)
Display information about a thread.

        if (t == null) return;
        out.println(indent + "Thread: " + t.getName() +
		    "  Priority: " + t.getPriority() +
		    (t.isDaemon()?" Daemon":"") +
		    (t.isAlive()?"":" Not Alive"));