I'm having an issue with Threads using netbeans Swing GUI. This is my first time really trying to develop a GUI for a backup program using Java's File System Notifier. I have two files SyncUI.java and Sync.java.
Pretty much what I want to happen is you enter a directory path in the jTextField1 text field which creates a sync thread that creates a new sync object and then calls processEvents on that object. When a file in that directory is changed I want to add text about the change to the list.
In its current state the UI is no longer not responding, however the processEvents isn't adding anything into my list. Any idea what the problem is? Also since I'm just starting to use java any constructive criticism is welcomed.
SyncUI.java:
package sync;
import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.DefaultListModel;
import javax.swing.JList;
import javax.swing.SwingUtilities;
public class SyncUI extends javax.swing.JFrame {
public SyncUI() {
initComponents();
}
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jButton1 = new javax.swing.JButton();
jTextField1 = new javax.swing.JTextField();
list1 = new java.awt.List();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jButton1.setText("Start");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton1ActionPerformed(evt);
}
});
jTextField1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jTextField1ActionPerformed(evt);
}
});
list1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
list1ActionPerformed(evt);
}
});
org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
.add(layout.createSequentialGroup()
.addContainerGap()
.add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
.add(list1, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.add(layout.createSequentialGroup()
.add(jTextField1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 329, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
.add(jButton1)
.add(0, 0, Short.MAX_VALUE)))
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
.add(layout.createSequentialGroup()
.addContainerGap()
.add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
.add(jButton1)
.add(jTextField1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
.add(list1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 229, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
.addContainerGap(25, Short.MAX_VALUE))
);
pack();
}// </editor-fold>
private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {
jButton1.doClick();
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
//I tried to use invokeLater, this solved the problem of the UI nonresponse issue
SwingUtilities.invokeLater(new Runnable() {
public void run()
{
//Creates a path dir that my Sync constructor needs to start file notification watcher on that directory
Path dir = Paths.get(jTextField1.getText());
try
{
//Creates a new sync object passing it the directory and the list in my GUI
Sync sync = new Sync(dir, list1);
try
{
sync.processEvents();
}
catch (InterruptedException ex)
{
Logger.getLogger(SyncUI.class.getName()).log(Level.SEVERE, null, ex);
}
}
catch (IOException ex)
{
Logger.getLogger(SyncUI.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
}
private void list1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}
public static void main(String args[]) throws IOException
{
java.awt.EventQueue.invokeLater(new Runnable()
{
public void run()
{
SyncUI s = new SyncUI();
s.setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton jButton1;
private javax.swing.JTextField jTextField1;
private java.awt.List list1;
// End of variables declaration
}
Sync.java:
package sync;
import static java.nio.file.StandardWatchEventKinds.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.nio.file.*;
import java.util.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.SwingUtilities;
public class Sync
{
private final WatchService ws;
private final Map<WatchKey,Path> keys;
public java.awt.List list;
public Sync(Path dir, java.awt.List list) throws IOException, InterruptedException
{
this.ws = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
this.list = list;
recSet(dir);
//this.processEvents();
}
private void register(Path dir) throws IOException
{
WatchKey key = dir.register(ws, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
keys.put(key, dir);
}
private void recSet(Path start) throws IOException
{
Files.walkFileTree(start, new SimpleFileVisitor<Path>()
{
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException
{
if(!Files.isHidden(dir))
{
register(dir);
System.out.println(dir);
}
return FileVisitResult.CONTINUE;
}
});
}
void processEvents() throws IOException, InterruptedException
{
System.out.println("Entered processEvents");
SwingUtilities.invokeLater(new Runnable() {
public void run()
{
System.out.println("Entered run");
list.add("test2");
list.repaint();
while(true)
{
WatchKey key;
try
{
key = ws.take();
}
catch (InterruptedException x)
{
return;
}
Path dir = keys.get(key);
if (dir == null)
{
System.err.println("WatchKey not recognized");
continue;
}
for (WatchEvent<?> event: key.pollEvents())
{
WatchEvent.Kind<?> kind = event.kind();
WatchEvent<Path> ev = (WatchEvent<Path>)event;
Path filename = ev.context();
String name = dir.resolve(filename).toString();
if (kind == OVERFLOW)
continue;
if(kind == ENTRY_CREATE)
{
System.out.print("Entry Created: ");
File f = new File(name);
if(f.isDirectory())
try {
register(dir.resolve(filename));
} catch (IOException ex) {
Logger.getLogger(Sync.class.getName()).log(Level.SEVERE, null, ex);
}
System.out.println(name);
list.add(name);
}
else if(kind == ENTRY_DELETE)
{
System.out.print("Entry Deleted: ");
System.out.println(name);
}
else if(kind == ENTRY_MODIFY)
{
File f = new File(name);
if(!f.isDirectory())
{
System.out.print("Entry Modify: ");
System.out.println(name);
}
}
boolean valid = key.reset();
if (!valid)
break;
}
}
}
});
}
}
Swing is not thread safe, so, if you are tryng to update a UI in the same thread you will have the "application freeze" behavior. To solve this, you need to delegate the process of update the UI to another thread. This is made using SwingUtilities.invokeLater (Java 5 and prior) method and/or the SwingWorker class (since Java 6).
Some links:
- http://docs.oracle.com/javase/tutorial/uiswing/concurrency/worker.html
- http://docs.oracle.com/javase/7/docs/api/javax/swing/SwingWorker.html
- http://java.sun.com/products/jfc/tsc/articles/threads/threads1.html
- http://forum.codecall.net/topic/56804-swing-thread-safety-how-to-properly-modify-components/
Google search: https://www.google.com.br/search?q=swing+thread+safe
In support of davidbuzatto:
No, I think you miss under stood what InvokeLater does. InvokeLater ensures that the runnable is executed ON the ETD. So basically, from what I can read, you've gone an put your long running, Event Blocking code right back in the ETD. Only use InvokeLater when you want to update the UI, use Threads or SwingWorker when you want to actually do processing
void processEvents() throws IOException, InterruptedException
{
System.out.println("Entered processEvents");
// PLEASE ETD, PUT THIS AT THE END OF THE QUEUE AND EXECUTE
// SO I RUN WITHIN YOUR CONTEXT
SwingUtilities.invokeLater(new Runnable() {
public void run()
{
// NOW RUNNING BACK ON THE ETD
System.out.println("Entered run");
list.add("test2");
list.repaint();
// NOW BLOCK THE ETD, SO NO MORE REPAINTS OR UPDATES WILL EVER
// OCCUR
while(true)
{
WatchKey key;
try
{
key = ws.take();
}
catch (InterruptedException x)
{
return;
}
Sorry for the caps, but I wanted the comments to standout.
1. Swing is Not Thread safe, but some methods like repaint(), setText() are Tread Safe.
2. The main() method in Swing is Not Long Lived. It schedules the construction of GUI in the Event Dispactcher Thread and then quits. Now its the responsibility of the EDT to handle the GUI.
3. You must keep your Non-UI work on your Non-UI thread, out off the GUI thread, ie EDT.
4. Your main() method should only do the work of making the JFrame visible, using EventQueue.invokeLater.
Eg:
public static void main(String[] args){
EventQueue.invokeLater(new Runnable(){
public void run(){
myFrame.setVisible(true);
}
}
}
5 SwingWorker is provided by Java to Synchronize the Work Output of the Non-UI thread on the GUI thread.
来源：https://stackoverflow.com/questions/11572726/java-awt-threads