- java.lang.Object
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- javax.swing.SwingWorker<T,V>
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- Type Parameters:
T- the result type returned by thisSwingWorker'sdoInBackgroundandgetmethodsV- the type used for carrying out intermediate results by thisSwingWorker'spublishandprocessmethods
- All Implemented Interfaces:
Runnable,Future<T>,RunnableFuture<T>
public abstract class SwingWorker<T,V> extends Object implements RunnableFuture<T>
An abstract class to perform lengthy GUI-interaction tasks in a background thread. Several background threads can be used to execute such tasks. However, the exact strategy of choosing a thread for any particularSwingWorkeris 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):
- Time-consuming tasks should not be run on the Event Dispatch Thread. Otherwise the application becomes unresponsive.
- Swing components should be accessed on the Event Dispatch Thread only.
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.
SwingWorkeris 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 ofSwingWorkermust implement thedoInBackground()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 schedulesSwingWorkerfor the execution on a worker thread and returns immediately. One can wait for theSwingWorkerto complete using thegetmethods. -
Worker thread: The
doInBackground()method is called on this thread. This is where all background activities should happen. To notifyPropertyChangeListenersabout bound properties changes use thefirePropertyChangeandgetPropertyChangeSupport()methods. By default there are two bound properties available:stateandprogress. -
Event Dispatch Thread: All Swing related activities occur on this thread.
SwingWorkerinvokes theprocessanddone()methods and notifies anyPropertyChangeListenerson this thread.
Often, the Current thread is the Event Dispatch Thread.
Before the
doInBackgroundmethod is invoked on a worker thread,SwingWorkernotifies anyPropertyChangeListenersabout thestateproperty change toStateValue.STARTED. After thedoInBackgroundmethod is finished thedonemethod is executed. ThenSwingWorkernotifies anyPropertyChangeListenersabout thestateproperty change toStateValue.DONE.SwingWorkeris only designed to be executed once. Executing aSwingWorkermore than once will not result in invoking thedoInBackgroundmethod 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> {@Overridepublic String doInBackground() { return findTheMeaningOfLife(); }@Overrideprotected 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 aJProgressBar. Finally, we also want to print the prime numbers toSystem.out.class PrimeNumbersTask extends SwingWorker<List<Integer>, Integer> { PrimeNumbersTask(JTextArea textArea, int numbersToFind) { //initialize }@Overridepublic List<Integer> doInBackground() { while (! enough && ! isCancelled()) { number = nextPrimeNumber(); publish(number); setProgress(100 * numbers.size() / numbersToFind); } } return numbers; }@Overrideprotected 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 gotBecause
SwingWorkerimplementsRunnable, aSwingWorkercan be submitted to anExecutorfor execution.- Since:
- 1.6
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Nested Class Summary
Nested Classes Modifier and Type Class Description static classSwingWorker.StateValueValues for thestatebound property.
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Constructor Summary
Constructors Constructor Description SwingWorker()Constructs thisSwingWorker.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description voidaddPropertyChangeListener(PropertyChangeListener listener)Adds aPropertyChangeListenerto the listener list.protected abstract TdoInBackground()Computes a result, or throws an exception if unable to do so.protected voiddone()Executed on the Event Dispatch Thread after thedoInBackgroundmethod is finished.voidexecute()Schedules thisSwingWorkerfor execution on a worker thread.voidfirePropertyChange(String propertyName, Object oldValue, Object newValue)Reports a bound property update to any registered listeners.Tget()Waits if necessary for the computation to complete, and then retrieves its result.Tget(long timeout, TimeUnit unit)Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.intgetProgress()Returns theprogressbound property.PropertyChangeSupportgetPropertyChangeSupport()Returns thePropertyChangeSupportfor thisSwingWorker.SwingWorker.StateValuegetState()Returns theSwingWorkerstate bound property.protected voidprocess(List<V> chunks)Receives data chunks from thepublishmethod asynchronously on the Event Dispatch Thread.protected voidpublish(V... chunks)Sends data chunks to theprocess(java.util.List<V>)method.voidremovePropertyChangeListener(PropertyChangeListener listener)Removes aPropertyChangeListenerfrom the listener list.voidrun()Sets thisFutureto the result of computation unless it has been cancelled.protected voidsetProgress(int progress)Sets theprogressbound property.-
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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Methods declared in interface java.util.concurrent.Future
cancel, isCancelled, isDone
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Method Detail
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doInBackground
protected abstract T doInBackground() throws Exception
Computes a result, or throws an exception if unable to do so.Note that this method is executed only once.
Note: this method is executed in a background thread.
- Returns:
- the computed result
- Throws:
Exception- if unable to compute a result
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run
public final void run()
Sets thisFutureto the result of computation unless it has been cancelled.- Specified by:
runin interfaceRunnable- Specified by:
runin interfaceRunnableFuture<T>- See Also:
Thread.run()
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publish
@SafeVarargs protected final void publish(V... chunks)
Sends data chunks to theprocess(java.util.List<V>)method. This method is to be used from inside thedoInBackgroundmethod to deliver intermediate results for processing on the Event Dispatch Thread inside theprocessmethod.Because the
processmethod is invoked asynchronously on the Event Dispatch Thread multiple invocations to thepublishmethod might occur before theprocessmethod 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
DefaultTableModelwith it. Note that it safe to mutate the tableModel from inside theprocessmethod 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; }@Overrideprotected DefaultTableModel doInBackground() throws Exception { for (Object[] row = loadData(); ! isCancelled() && row != null; row = loadData()) { publish((Object[]) row); } return tableModel; }@Overrideprotected void process(List<Object[]> chunks) { for (Object[] row : chunks) { tableModel.addRow(row); } } }- Parameters:
chunks- intermediate results to process- See Also:
process(java.util.List<V>)
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process
protected void process(List<V> chunks)
Receives data chunks from thepublishmethod asynchronously on the Event Dispatch Thread.Please refer to the
publish(V...)method for more details.- Parameters:
chunks- intermediate results to process- See Also:
publish(V...)
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done
protected void done()
Executed on the Event Dispatch Thread after thedoInBackgroundmethod 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.- See Also:
doInBackground(),Future.isCancelled(),get()
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setProgress
protected final void setProgress(int progress)
Sets theprogressbound property. The value should be from 0 to 100.Because
PropertyChangeListeners are notified asynchronously on the Event Dispatch Thread multiple invocations to thesetProgressmethod might occur before anyPropertyChangeListenersare invoked. For performance purposes all these invocations are coalesced into one invocation with the last invocation argument only.For example, the following invokations:
setProgress(1); setProgress(2); setProgress(3);
might result in a singlePropertyChangeListenernotification with the value3.- Parameters:
progress- the progress value to set- Throws:
IllegalArgumentException- is value not from 0 to 100
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getProgress
public final int getProgress()
Returns theprogressbound property.- Returns:
- the progress bound property.
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execute
public final void execute()
Schedules thisSwingWorkerfor execution on a worker thread. There are a number of worker threads available. In the event all worker threads are busy handling otherSwingWorkersthisSwingWorkeris placed in a waiting queue.Note:
SwingWorkeris only designed to be executed once. Executing aSwingWorkermore than once will not result in invoking thedoInBackgroundmethod twice.
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get
public final T get() throws InterruptedException, ExecutionException
Waits if necessary for the computation to complete, and then retrieves its result.Note: calling
geton the Event Dispatch Thread blocks all events, including repaints, from being processed until thisSwingWorkeris complete.When you want the
SwingWorkerto 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);- Specified by:
getin interfaceFuture<T>- Returns:
- the computed result
- Throws:
CancellationException- if the computation was cancelledInterruptedException- if the current thread was interrupted while waitingExecutionException- if the computation threw an exception
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get
public final T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.Please refer to
get()for more details.- Specified by:
getin interfaceFuture<T>- Parameters:
timeout- the maximum time to waitunit- the time unit of the timeout argument- Returns:
- the computed result
- Throws:
CancellationException- if the computation was cancelledInterruptedException- if the current thread was interrupted while waitingExecutionException- if the computation threw an exceptionTimeoutException- if the wait timed out
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addPropertyChangeListener
public final void addPropertyChangeListener(PropertyChangeListener listener)
Adds aPropertyChangeListenerto 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. Iflistenerisnull, no exception is thrown and no action is taken.Note: This is merely a convenience wrapper. All work is delegated to
PropertyChangeSupportfromgetPropertyChangeSupport().- Parameters:
listener- thePropertyChangeListenerto be added
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removePropertyChangeListener
public final void removePropertyChangeListener(PropertyChangeListener listener)
Removes aPropertyChangeListenerfrom the listener list. This removes aPropertyChangeListenerthat was registered for all properties. Iflistenerwas added more than once to the same event source, it will be notified one less time after being removed. Iflistenerisnull, 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
PropertyChangeSupportfromgetPropertyChangeSupport().- Parameters:
listener- thePropertyChangeListenerto be removed
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firePropertyChange
public final void firePropertyChange(String propertyName, Object oldValue, Object newValue)
Reports a bound property update to any registered listeners. No event is fired ifoldandneware equal and non-null.This
SwingWorkerwill be the source for any generated events.When called off the Event Dispatch Thread
PropertyChangeListenersare notified asynchronously on the Event Dispatch Thread.Note: This is merely a convenience wrapper. All work is delegated to
PropertyChangeSupportfromgetPropertyChangeSupport().- Parameters:
propertyName- the programmatic name of the property that was changedoldValue- the old value of the propertynewValue- the new value of the property
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getPropertyChangeSupport
public final PropertyChangeSupport getPropertyChangeSupport()
Returns thePropertyChangeSupportfor thisSwingWorker. This method is used when flexible access to bound properties support is needed.This
SwingWorkerwill be the source for any generated events.Note: The returned
PropertyChangeSupportnotifies anyPropertyChangeListeners asynchronously on the Event Dispatch Thread in the event thatfirePropertyChangeorfireIndexedPropertyChangeare called off the Event Dispatch Thread.- Returns:
PropertyChangeSupportfor thisSwingWorker
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getState
public final SwingWorker.StateValue getState()
Returns theSwingWorkerstate bound property.- Returns:
- the current state
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