在多线程Swing程序中频繁调用setText（）

Question

I have a Swing program where work is continuously being done in a non-Swing thread. It often needs to update a JTextPane -- frequently many times per second. I realize that setText() needs to be called from back inside the event-dispatching thread, but I cant figure out how to make this happen smoothly.

The following minimal complete example is as close as I've been able to get it, using a PipedInputStream/PipedOutputStream pair, but this only seems to update the screen once every second or so. I'm not sure what's taking so long.

import java.awt.event.*;
import javax.swing.*;
import java.io.*;

public class TextTest extends JFrame {
    private JTextPane out = new JTextPane();
    private PipedInputStream pIn = new PipedInputStream();
    private PrintWriter pOut;

    public TextTest() {
        try {
            pOut = new PrintWriter(new PipedOutputStream(pIn));
        }
        catch (IOException e) {System.err.println("can't init stream");}

        add(new JScrollPane(out));
        setSize(500, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);

        // Start a loop to print to the stream continuously
        new Thread() {
            public void run() {
                for (int i = 0; true; i++) {
                    pOut.println(i);
                }
            }
        }.start();

        // Start a timer to display the text in the stream every 10 ms
        new Timer(10, new ActionListener() {
            public void actionPerformed (ActionEvent evt) {
                try {
                    if (pIn.available() > 0) {
                        byte[] buffer = new byte[pIn.available()];
                        pIn.read(buffer);
                        out.setText(out.getText() + new String(buffer));
                    }
                }
                catch (IOException e) {System.err.println("can't read stream");}
            }
        }).start();
    }

    public static void main(String[] args) {
        new TextTest();
    }
}

Am I implementing this wrong? Do I just have totally the wrong idea about how to continuously update a JTextPane from outside the EDT?

Answer 1

The setText() "method is thread safe, although most Swing methods are not. Please see How to Use Threads for more information."

Addendum: For reference, here's some other approaches to updating on the EDT. Another thing to note is that the action event handler for javax.swing.Timer executes on the EDT. Here's my variation:

import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import javax.swing.text.DefaultCaret;

public class TextTest extends JFrame {

    private JTextArea out = new JTextArea();
    private PipedInputStream pIn = new PipedInputStream();
    private PrintWriter pOut;

    public TextTest() {
        try {
            pOut = new PrintWriter(new PipedOutputStream(pIn));
        } catch (IOException e) {
            System.err.println("can't init stream");
        }

        DefaultCaret caret = (DefaultCaret) out.getCaret();
        caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

        add(new JScrollPane(out));
        setSize(300, 500);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);

        // Start a loop to print to the stream continuously
        new Thread() {

            public void run() {
                for (int i = 0; true; i++) {
                    pOut.println(i);
                }
            }
        }.start();

        // Start a timer to display the text in the stream every 10 ms
        new Timer(10, new ActionListener() {

            public void actionPerformed(ActionEvent evt) {
                try {
                    out.append(String.valueOf((char) pIn.read()));
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

    public static void main(String[] args) {
        new TextTest();
    }
}

Answer 2

you need to flush the output of your printWriter and i'd suggest a small pause in your thread given its a tight for loop to let the update thread kick in once in a while.

 pOut.println(i); 
 pOut.flush();
 try {
      sleep(10);
 } catch (InterruptedException e) {
 }

This will give a smoother flow.

Answer 3

but this only seems to update the screen once every second or so. I'm not sure what's taking so long.

System.out.println(pIn.available());

I added the above statement to the actionPerformed code of the Timer. Nothing happens until the buffer reaches 1024 bytes. So somehow I guess you need to change the buffer size.

Also, you should not be using setText(). It is inefficient to recreate the Document every time you make a change.

You could use:

out.replaceSelection(new String(buffer) );

Or the more common approach is to use:

Document doc = textPane.getDocument();
doc.insertString("...", doc.getLength(), null);

Don't think the insertString() method is thread safe, but the replaceSelection() method is.

Edit:

Just tried playing with a buffer size of 10 in the input stream and flushing the ouput stream and it didn't make any difference, so I guess I don't understand piped streams.

Answer 4

The proper tutorial link for concurrency and Swing looks like it's here: Lesson: Concurrency in Swing

@camickr: setText does not create a new document, it effectively does either this:

doc.replace(0, doc.getLength(), s, null);

or this:

doc.remove(0, doc.getLength());
doc.insertString(0, s, null);

I'm not claiming that it's efficient however...

Another thing that setText does not do is to cause revalidate() and repaint() to be issued ( setDocument does, however). It's probably worthwhile to add those two calls after the call to setText .