T
- the result type returned by this SwingWorker's
doInBackground
and get
methodsV
- the type used for carrying out intermediate results by this SwingWorker's
publish
and process
methodsRunnable
, Future<T>
, RunnableFuture<T>
public abstract class SwingWorker<T,V> extends Object implements RunnableFuture<T>
SwingWorker
is unspecified and should not be relied on. When writing a multi-threaded application using Swing, there are two constraints to keep in mind: (refer to Concurrency in Swing for more details):
These constraints mean that a GUI application with time intensive computing needs at least two threads: 1) a thread to perform the lengthy task and 2) the Event Dispatch Thread (EDT) for all GUI-related activities. This involves inter-thread communication which can be tricky to implement.
SwingWorker
is designed for situations where you need to have a long running task run in a background thread and provide updates to the UI either when done, or while processing. Subclasses of SwingWorker
must implement the doInBackground()
method to perform the background computation.
Workflow
There are three threads involved in the life cycle of a SwingWorker
:
Current thread: The execute()
method is called on this thread. It schedules SwingWorker
for the execution on a worker thread and returns immediately. One can wait for the SwingWorker
to complete using the get
methods.
Worker thread: The doInBackground()
method is called on this thread. This is where all background activities should happen. To notify PropertyChangeListeners
about bound properties changes use the firePropertyChange
and getPropertyChangeSupport()
methods. By default there are two bound properties available: state
and progress
.
Event Dispatch Thread: All Swing related activities occur on this thread. SwingWorker
invokes the process
and done()
methods and notifies any PropertyChangeListeners
on this thread.
Often, the Current thread is the Event Dispatch Thread.
Before the doInBackground
method is invoked on a worker thread, SwingWorker
notifies any PropertyChangeListeners
about the state
property change to StateValue.STARTED
. After the doInBackground
method is finished the done
method is executed. Then SwingWorker
notifies any PropertyChangeListeners
about the state
property change to StateValue.DONE
.
SwingWorker
is only designed to be executed once. Executing a SwingWorker
more than once will not result in invoking the doInBackground
method twice.
Sample Usage
The following example illustrates the simplest use case. Some processing is done in the background and when done you update a Swing component.
Say we want to find the "Meaning of Life" and display the result in a JLabel
.
final JLabel label; class MeaningOfLifeFinder extends SwingWorker<String, Object> {@Override
public String doInBackground() { return findTheMeaningOfLife(); }@Override
protected void done() { try { label.setText(get()); } catch (Exception ignore) { } } } (new MeaningOfLifeFinder()).execute();
The next example is useful in situations where you wish to process data as it is ready on the Event Dispatch Thread.
Now we want to find the first N prime numbers and display the results in a JTextArea
. While this is computing, we want to update our progress in a JProgressBar
. Finally, we also want to print the prime numbers to System.out
.
class PrimeNumbersTask extends SwingWorker<List<Integer>, Integer> { PrimeNumbersTask(JTextArea textArea, int numbersToFind) { //initialize }@Override
public List<Integer> doInBackground() { while (! enough && ! isCancelled()) { number = nextPrimeNumber(); publish(number); setProgress(100 * numbers.size() / numbersToFind); } } return numbers; }@Override
protected void process(List<Integer> chunks) { for (int number : chunks) { textArea.append(number + "\n"); } } } JTextArea textArea = new JTextArea(); final JProgressBar progressBar = new JProgressBar(0, 100); PrimeNumbersTask task = new PrimeNumbersTask(textArea, N); task.addPropertyChangeListener( new PropertyChangeListener() { public void propertyChange(PropertyChangeEvent evt) { if ("progress".equals(evt.getPropertyName())) { progressBar.setValue((Integer)evt.getNewValue()); } } }); task.execute(); System.out.println(task.get()); //prints all prime numbers we have got
Because SwingWorker
implements Runnable
, a SwingWorker
can be submitted to an Executor
for execution.
Modifier and Type | Class | Description |
---|---|---|
static enum |
SwingWorker.StateValue |
Values for the state bound property. |
Future.State
Constructor | Description |
---|---|
SwingWorker() |
Constructs this SwingWorker . |
Modifier and Type | Method | Description |
---|---|---|
final void |
addPropertyChangeListener |
Adds a PropertyChangeListener to the listener list. |
final boolean |
cancel |
Attempts to cancel execution of this task. |
protected abstract T |
doInBackground() |
Computes a result, or throws an exception if unable to do so. |
protected void |
done() |
Executed on the Event Dispatch Thread after the doInBackground method is finished. |
final void |
execute() |
Schedules this SwingWorker for execution on a worker thread. |
final void |
firePropertyChange |
Reports a bound property update to any registered listeners. |
final T |
get() |
Waits if necessary for the computation to complete, and then retrieves its result. |
final T |
get |
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available. |
final int |
getProgress() |
Returns the progress bound property. |
final PropertyChangeSupport |
getPropertyChangeSupport() |
Returns the PropertyChangeSupport for this SwingWorker . |
final SwingWorker.StateValue |
getState() |
Returns the SwingWorker state bound property. |
final boolean |
isCancelled() |
Returns true if this task was cancelled before it completed normally. |
final boolean |
isDone() |
Returns true if this task completed. |
protected void |
process |
Receives data chunks from the publish method asynchronously on the Event Dispatch Thread. |
protected final void |
publish |
Sends data chunks to the process(java.util.List<V>) method. |
final void |
removePropertyChangeListener |
Removes a PropertyChangeListener from the listener list. |
final void |
run() |
Sets this Future to the result of computation unless it has been cancelled. |
protected final void |
setProgress |
Sets the progress bound property. |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
exceptionNow, resultNow, state
public SwingWorker()
SwingWorker
.protected abstract T doInBackground() throws Exception
Note that this method is executed only once.
Note: this method is executed in a background thread.
Exception
- if unable to compute a resultpublic final void run()
Future
to the result of computation unless it has been cancelled.run
in interface Runnable
run
in interface RunnableFuture<T>
@SafeVarargs protected final void publish(V... chunks)
process(java.util.List<V>)
method. This method is to be used from inside the doInBackground
method to deliver intermediate results for processing on the Event Dispatch Thread inside the process
method. Because the process
method is invoked asynchronously on the Event Dispatch Thread multiple invocations to the publish
method might occur before the process
method is executed. For performance purposes all these invocations are coalesced into one invocation with concatenated arguments.
For example:
publish("1"); publish("2", "3"); publish("4", "5", "6");might result in:
process("1", "2", "3", "4", "5", "6")
Sample Usage. This code snippet loads some tabular data and updates DefaultTableModel
with it. Note that it safe to mutate the tableModel from inside the process
method because it is invoked on the Event Dispatch Thread.
class TableSwingWorker extends SwingWorker<DefaultTableModel, Object[]> { private final DefaultTableModel tableModel; public TableSwingWorker(DefaultTableModel tableModel) { this.tableModel = tableModel; }@Override
protected DefaultTableModel doInBackground() throws Exception { for (Object[] row = loadData(); ! isCancelled() && row != null; row = loadData()) { publish((Object[]) row); } return tableModel; }@Override
protected void process(List<Object[]> chunks) { for (Object[] row : chunks) { tableModel.addRow(row); } } }
chunks
- intermediate results to processprotected void process(List<V> chunks)
publish
method asynchronously on the Event Dispatch Thread. Please refer to the publish(V...)
method for more details.
chunks
- intermediate results to processprotected void done()
doInBackground
method is finished. The default implementation does nothing. Subclasses may override this method to perform completion actions on the Event Dispatch Thread. Note that you can query status inside the implementation of this method to determine the result of this task or whether this task has been cancelled.protected final void setProgress(int progress)
progress
bound property. The value should be from 0 to 100. Because PropertyChangeListener
s are notified asynchronously on the Event Dispatch Thread multiple invocations to the setProgress
method might occur before any PropertyChangeListeners
are invoked. For performance purposes all these invocations are coalesced into one invocation with the last invocation argument only.
For example, the following invocations:
setProgress(1); setProgress(2); setProgress(3);might result in a single
PropertyChangeListener
notification with the value 3
.progress
- the progress value to setIllegalArgumentException
- is value not from 0 to 100public final int getProgress()
progress
bound property.public final void execute()
SwingWorker
for execution on a worker thread. There are a number of worker threads available. In the event all worker threads are busy handling other SwingWorkers
this SwingWorker
is placed in a waiting queue. Note: SwingWorker
is only designed to be executed once. Executing a SwingWorker
more than once will not result in invoking the doInBackground
method twice.
public final boolean cancel(boolean mayInterruptIfRunning)
cancel
is called, this task should never run. If the task has already started, then the mayInterruptIfRunning
parameter determines whether the thread executing this task (when known by the implementation) is interrupted in an attempt to stop the task. The return value from this method does not necessarily indicate whether the task is now cancelled; use Future.isCancelled()
.
cancel
in interface Future<T>
mayInterruptIfRunning
- true
if the thread executing this task should be interrupted (if the thread is known to the implementation); otherwise, in-progress tasks are allowed to completefalse
if the task could not be cancelled, typically because it has already completed; true
otherwise. If two or more threads cause a task to be cancelled, then at least one of them returns true
. Implementations may provide stronger guarantees.public final boolean isCancelled()
true
if this task was cancelled before it completed normally.isCancelled
in interface Future<T>
true
if this task was cancelled before it completedpublic final boolean isDone()
true
if this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will return true
.public final T get() throws InterruptedException, ExecutionException
Note: calling get
on the Event Dispatch Thread blocks all events, including repaints, from being processed until this SwingWorker
is complete.
When you want the SwingWorker
to block on the Event Dispatch Thread we recommend that you use a modal dialog.
For example:
class SwingWorkerCompletionWaiter implements PropertyChangeListener { private JDialog dialog; public SwingWorkerCompletionWaiter(JDialog dialog) { this.dialog = dialog; } public void propertyChange(PropertyChangeEvent event) { if ("state".equals(event.getPropertyName()) && SwingWorker.StateValue.DONE == event.getNewValue()) { dialog.setVisible(false); dialog.dispose(); } } } JDialog dialog = new JDialog(owner, true); swingWorker.addPropertyChangeListener( new SwingWorkerCompletionWaiter(dialog)); swingWorker.execute(); //the dialog will be visible until the SwingWorker is done dialog.setVisible(true);
get
in interface Future<T>
CancellationException
- if the computation was cancelledInterruptedException
- if the current thread was interrupted while waitingExecutionException
- if the computation threw an exceptionpublic final T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
Please refer to get()
for more details.
get
in interface Future<T>
timeout
- the maximum time to waitunit
- the time unit of the timeout argumentCancellationException
- if the computation was cancelledInterruptedException
- if the current thread was interrupted while waitingExecutionException
- if the computation threw an exceptionTimeoutException
- if the wait timed outpublic final void addPropertyChangeListener(PropertyChangeListener listener)
PropertyChangeListener
to the listener list. The listener is registered for all properties. The same listener object may be added more than once, and will be called as many times as it is added. If listener
is null
, no exception is thrown and no action is taken. Note: This is merely a convenience wrapper. All work is delegated to PropertyChangeSupport
from getPropertyChangeSupport()
.
listener
- the PropertyChangeListener
to be addedpublic final void removePropertyChangeListener(PropertyChangeListener listener)
PropertyChangeListener
from the listener list. This removes a PropertyChangeListener
that was registered for all properties. If listener
was added more than once to the same event source, it will be notified one less time after being removed. If listener
is null
, or was never added, no exception is thrown and no action is taken. Note: This is merely a convenience wrapper. All work is delegated to PropertyChangeSupport
from getPropertyChangeSupport()
.
listener
- the PropertyChangeListener
to be removedpublic final void firePropertyChange(String propertyName, Object oldValue, Object newValue)
old
and new
are equal and non-null. This SwingWorker
will be the source for any generated events.
When called off the Event Dispatch Thread PropertyChangeListeners
are notified asynchronously on the Event Dispatch Thread.
Note: This is merely a convenience wrapper. All work is delegated to PropertyChangeSupport
from getPropertyChangeSupport()
.
propertyName
- the programmatic name of the property that was changedoldValue
- the old value of the propertynewValue
- the new value of the propertypublic final PropertyChangeSupport getPropertyChangeSupport()
PropertyChangeSupport
for this SwingWorker
. This method is used when flexible access to bound properties support is needed. This SwingWorker
will be the source for any generated events.
Note: The returned PropertyChangeSupport
notifies any PropertyChangeListener
s asynchronously on the Event Dispatch Thread in the event that firePropertyChange
or fireIndexedPropertyChange
are called off the Event Dispatch Thread.
PropertyChangeSupport
for this SwingWorker
public final SwingWorker.StateValue getState()
SwingWorker
state bound property.
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