Threads, and the UI question.

[Dan Patterson]

There is something I am not understanding with this, so here goes.

First I am going to post the code which is in 3 classes. Then i'll ask the question at the bottom.

First OrderVod.java

  
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
/*
 * OrderVod.java is a 1.5 application that requires these files:
 *   VodTask.java
 *   SwingWorker.java
 */
public class OrderVod extends JPanel
                      implements ActionListener {
    public final static int ONE_SECOND = 1000;
    public  JTextField enterIp;
    
    private JProgressBar progressBar;
    private JLabel enterIpLabel;
    private Timer timer;
    private JButton runButton;
    private JButton cancelButton;
    private VodTask task;
    private JTextArea taskOutput;
    private String newline = "\n";
 
    public OrderVod() {
        super(new BorderLayout());
        task = new VodTask();
 
        //Create the UI.
        runButton = new JButton("Run");
        runButton.setActionCommand("run");
        runButton.addActionListener(this);
        
        cancelButton = new JButton("Cancel");
        cancelButton.setActionCommand("cancel");
        cancelButton.addActionListener(this);
        
        enterIp = new JTextField(16);
        enterIpLabel = new JLabel("Enter the I.P Address of the Set-top");
 
        progressBar = new JProgressBar(0, task.getLengthOfTask());
        progressBar.setValue(0);
        progressBar.setStringPainted(true);
 
        taskOutput = new JTextArea(20, 70);
        taskOutput.setMargin(new Insets(20,20,20,20));
        taskOutput.setEditable(false);
        taskOutput.setCursor(null); 
                                    
 
        JPanel panel = new JPanel();
        panel.add(enterIpLabel);
        panel.add(enterIp);
        panel.add(runButton);
        panel.add(cancelButton);
        panel.add(progressBar);
 
        add(panel, BorderLayout.PAGE_START);
        add(new JScrollPane(taskOutput), BorderLayout.CENTER);
        setBorder(BorderFactory.createEmptyBorder(70, 70, 70, 70));
 
        //Create a timer.
        timer = new Timer(ONE_SECOND, new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                progressBar.setValue(task.getCurrent());
                String s = task.getMessage();
                if (s != null) {
                    taskOutput.append(s + newline);
                    taskOutput.setCaretPosition(
                            taskOutput.getDocument().getLength());
                }
                if (task.isDone()) {
                    Toolkit.getDefaultToolkit().beep();
                    timer.stop();
                    runButton.setEnabled(true);
                    setCursor(null); 
                    progressBar.setValue(progressBar.getMinimum());
                }
            }
        });
    }
 
    /**
     * Called when the user presses the run button.
     */
    public void actionPerformed(ActionEvent evt) {
        runButton.setEnabled(false);
        setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
        task.go();
        timer.start();
    }
 
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        
        JFrame.setDefaultLookAndFeelDecorated(true);
 
        
        JFrame frame = new JFrame("OrderVod");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        
        JComponent newContentPane = new OrderVod();
        newContentPane.setOpaque(true); 
        frame.setContentPane(newContentPane);
 
        
        frame.pack();
        frame.setVisible(true);
    }
 
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}
 

then VodTask.java

 
/* 
 * VodTask.java is used by:
 *   OrderVod.java
 */
public class VodTask {
    private int lengthOfTask;
    private int current = 0;
    private boolean done = false;
    private boolean canceled = false;
    private String statMessage;
    
    public VodTask() {
        //Compute length of task...
        //In a real program, this would figure out
        //the number of bytes to read or whatever.
        lengthOfTask = 1000;
    }
 
    /**
     * Called from OrderVod to start the task.
     */
    public void go() {
        final SwingWorker worker = new SwingWorker() {
            public Object construct() {
                current = 0;
                done = false;
                canceled = false;
                statMessage = null;
                return new ActualTask();
            }
        };
        worker.start();
    }
 
    /**
     * Called from OrderVod to find out how much work needs
     * to be done.
     */
    public int getLengthOfTask() {
        return lengthOfTask;
    }
 
    /**
     * Called from OrderVod to find out how much has been done.
     */
    public int getCurrent() {
        return current;
    }
 
    public void stop() {
        canceled = true;
        statMessage = null;
    }
 
    /**
     * Called from OrderVod to find out if the task has completed.
     */
    public boolean isDone() {
        return done;
    }
 
    /**
     * Returns the most recent status message, or null
     * if there is no current status message.
     */
    public String getMessage() {
        return statMessage;
    }
 
    /**
     * The actual long running task.  This runs in a SwingWorker thread.
     */
    class ActualTask {
        ActualTask() {
            //Fake a long task,
            //making a random amount of progress every second.
            
            while (!canceled && !done) {
                try {
                    Thread.sleep(1000); //sleep for a second
                    current += Math.random() * 100; //make some progress
                    if (current >= lengthOfTask) {
                        done = true;
                        current = lengthOfTask;
                    }
                    statMessage = "Completed " + current +
                                  " out of " + lengthOfTask + ".";
                } catch (InterruptedException e) {
                    System.out.println("ActualTask interrupted");
                }
            }
        }
    }
}
 

then the SwingWorker.

import javax.swing.SwingUtilities;
 

public abstract class SwingWorker {
    private Object value;  // see getValue(), setValue()
 
    /** 
     * Class to maintain reference to current worker thread
     * under separate synchronization control.
     */
    private static class ThreadVar {
        private Thread thread;
        ThreadVar(Thread t) { thread = t; }
        synchronized Thread get() { return thread; }
        synchronized void clear() { thread = null; }
    }
 
    private ThreadVar threadVar;
 
    /** 
     * Get the value produced by the worker thread, or null if it 
     * hasn't been constructed yet.
     */
    protected synchronized Object getValue() { 
        return value; 
    }
 
    /** 
     * Set the value produced by worker thread 
     */
    private synchronized void setValue(Object x) { 
        value = x; 
    }
 
    /** 
     * Compute the value to be returned by the <code>get</code> method. 
     */
    public abstract Object construct();
 
    /**
     * Called on the event dispatching thread (not on the worker thread)
     * after the <code>construct</code> method has returned.
     */
    public void finished() {
    }
 
    /**
     * A new method that interrupts the worker thread.  Call this method
     * to force the worker to stop what it's doing.
     */
    public void interrupt() {
        Thread t = threadVar.get();
        if (t != null) {
            t.interrupt();
        }
        threadVar.clear();
    }
 
    /**
     * Return the value created by the <code>construct</code> method.  
     * Returns null if either the constructing thread or the current
     * thread was interrupted before a value was produced.
     * 
     * @return the value created by the <code>construct</code> method
     */
    public Object get() {
        while (true) {  
            Thread t = threadVar.get();
            if (t == null) {
                return getValue();
            }
            try {
                t.join();
            }
            catch (InterruptedException e) {
                Thread.currentThread().interrupt(); // propagate
                return null;
            }
        }
    }
 

    /**
     * Start a thread that will call the <code>construct</code> method
     * and then exit.
     */
    public SwingWorker() {
        final Runnable doFinished = new Runnable() {
           public void run() { finished(); }
        };
 
        Runnable doConstruct = new Runnable() { 
            public void run() {
                try {
                    setValue(construct());
                }
                finally {
                    threadVar.clear();
                }
 
                SwingUtilities.invokeLater(doFinished);
            }
        };
 
        Thread t = new Thread(doConstruct);
        threadVar = new ThreadVar(t);
    }
 
    /**
     * Start the worker thread.
     */
    public void start() {
        Thread t = threadVar.get();
        if (t != null) {
            t.start();
        }
    }
}
 

Ok What I am trying to do is run a shell script and have the output of the script show up in realtime in the JTextArea. What I am not sure about is where my code should go that is performing that task. Here is that code.

public void runRun() {
      
      String ip = enterIp.getText();
      String line = "";
      String NL = System.getProperty("line.separator");
 
     try {
          Process child = new ProcessBuilder("testvodscript",(ip)).start();
            
          BufferedReader input = new BufferedReader(new
          InputStreamReader(child.getInputStream()));         
            
            while((line = input.readLine()) != null) {
                   text.append(line + NL);
 }
 
             
}            catch (IOException e) {
                e.printStackTrace();
                System.exit(1);
}          catch  (SecurityException se) {
                    se.printStackTrace();
                    System.exit(1);
}            catch (NullPointerException npe) {
                    System.out.println("Null Pointer Exception");
                    System.exit(1);
}            catch (IllegalArgumentException iae) {
                    iae.printStackTrace();
                    System.exit(1);
 }
} 
 

The first 3 files are not completely my writings, I found code similar to what I am trying to do and changed it to how I wanted it. So what i need to figure out is when the run button is pushed i want this code above to run and the progress bar to tell the progress of it. Any help is much appreciated. Thanks, Sorry for the long post.

[Neeraj Dheer]

I think it should go in the actionPerformed(...) method in OrderVod.java

 /**     
* Called when the user presses the run button.     
*/    
 
public void actionPerformed(ActionEvent evt) { 
       runButton.setEnabled(false);
        setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
         task.go();
        timer.start();
//add call here, after u start the timer.  
 
}  

i hope that helps.