- All Implemented Interfaces:
Runnable
,Future<V>
,RunnableFuture<V>
,Worker<V>
,EventTarget
public abstract class Task<V> extends FutureTask<V> implements Worker<V>, EventTarget
A fully observable implementation of a FutureTask
. Task
exposes
additional state and observable properties useful for programming asynchronous
tasks in JavaFX, as defined in the Worker
interface. An implementation
of Task must override the call()
method. This method
is invoked on the background thread. Any state which is used in this method
must be safe to read and write from a background thread. For example, manipulating
a live scene graph from this method is unsafe and will result in runtime
exceptions.
Tasks are flexible and extremely useful for the encapsulation of "work". Because
Service
is designed to execute a Task, any Tasks defined by the application
or library code can easily be used with a Service. Likewise, since Task extends
from FutureTask, it is very easy and natural to use a Task with the java concurrency
Executor
API. Since a Task is Runnable, you
can also call it directly (by invoking the FutureTask.run()
method)
from another background thread. This allows for composition of work, or pass it to
a new Thread constructed and executed manually. Finally, since you can
manually create a new Thread, passing it a Runnable, it is possible to use
the following idiom:
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
Note that this code sets the daemon flag of the Thread to true. If you want a background thread to prevent the VM from exiting after the last stage is closed, then you would want daemon to be false. However, if you want the background threads to simply terminate after all the stages are closed, then you must set daemon to true.
Although ExecutorService
defines several methods which
take a Runnable, you should generally limit yourself to using the execute
method inherited from Executor
.
As with FutureTask, a Task is a one-shot class and cannot be reused. See Service
for a reusable Worker
.
Because the Task is designed for use with JavaFX GUI applications, it ensures
that every change to its public properties, as well as change notifications
for state, errors, and for event handlers, all occur on the main JavaFX application
thread. Accessing these properties from a background thread (including the
call()
method) will result in runtime exceptions being raised. The only exception
to this, is when initially configuring a Task, which may safely be done
from any thread. However, once the Task has been initialized and
started, it may only thereafter be used from the FX thread (except for those methods clearly
marked as being appropriate for the subclass to invoke from the background thread).
It is strongly encouraged that all Tasks be initialized with immutable state upon which the Task will operate. This should be done by providing a Task constructor which takes the parameters necessary for execution of the Task. Immutable state makes it easy and safe to use from any thread and ensures correctness in the presence of multiple threads.
In Java there is no reliable way to "kill" a thread in process. However,
when cancel
is called on a Task, it is important that
the Task stop processing. A "run-away" Task might continue processing
and updating the message, text, and progress properties even after the
Task has been cancelled! In Java, cancelling a Task is a cooperative
endeavor. The user of the Task will request that it be cancelled, and
the author of the Task must check whether is has been cancelled within
the body of the call
method. There are two ways this can
be done. First, the Task author may check the isCancelled method,
inherited from FutureTask
, to see whether the Task has
been cancelled. Second, if the Task implementation makes use of any
blocking calls (such as NIO InterruptibleChannels or Thread.sleep) and
the task is cancelled while in such a blocking call, an
InterruptedException is thrown. Task implementations which have blocking
calls should recognize that an interrupted thread may be the signal for
a cancelled task and should double check the isCancelled method to ensure
that the InterruptedException was thrown due to the cancellation of the
Task.
Examples
The following set of examples demonstrate some of the most common uses of Tasks.
A Simple Loop
The first example is a simple loop that does nothing particularly useful, but demonstrates the fundamental aspects of writing a Task correctly. This example will simply loop and print to standard out on each loop iteration. When it completes, it returns the number of times it iterated.
Task<Integer> task = new Task<Integer>() {
@Override protected Integer call() throws Exception {
int iterations;
for (iterations = 0; iterations < 100000; iterations++) {
if (isCancelled()) {
break;
}
System.out.println("Iteration " + iterations);
}
return iterations;
}
};
First, we define what type of value is returned from this Task. In this
case, we want to return the number of times we iterated, so we will
specify the Task to be of type Integer by using generics. Then, within
the implementation of the call
method, we iterate from
0 to 100000. On each iteration, we check to see whether this Task has
been cancelled. If it has been, then we break out of the loop and return
the number of times we iterated. Otherwise a message is printed to
the console and the iteration count increased and we continue looping.
Checking for isCancelled() in the loop body is critical, otherwise the
developer may cancel the task, but the task will continue running
and updating both the progress and returning the incorrect result
from the end of the call
method. A correct implementation
of a Task will always check for cancellation.
A Simple Loop With Progress Notification
Similar to the previous example, except this time we will modify the progress of the Task in each iteration. Note that we have a choice to make in the case of cancellation. Do we want to set the progress back to -1 (indeterminate) when the Task is cancelled, or do we want to leave the progress where it was at? In this case, let's leave the progress alone and only update the message on cancellation, though updating the progress after cancellation is a perfectly valid choice.
Task<Integer> task = new Task<Integer>() {
@Override protected Integer call() throws Exception {
int iterations;
for (iterations = 0; iterations < 10000000; iterations++) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
updateMessage("Iteration " + iterations);
updateProgress(iterations, 10000000);
}
return iterations;
}
};
As before, within the for loop we check whether the Task has been cancelled. If it has been cancelled, we will update the Task's message to indicate that it has been cancelled, and then break as before. If the Task has not been cancelled, then we will update its message to indicate the current iteration and then update the progress to indicate the current progress.
A Simple Loop With Progress Notification And Blocking Calls
This example adds to the previous examples a blocking call. Because a blocking call may thrown an InterruptedException, and because an InterruptedException may occur as a result of the Task being cancelled, we need to be sure to handle the InterruptedException and check on the cancel state.
Task<Integer> task = new Task<Integer>() {
@Override protected Integer call() throws Exception {
int iterations;
for (iterations = 0; iterations < 1000; iterations++) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
updateMessage("Iteration " + iterations);
updateProgress(iterations, 1000);
// Now block the thread for a short time, but be sure
// to check the interrupted exception for cancellation!
try {
Thread.sleep(100);
} catch (InterruptedException interrupted) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
}
}
return iterations;
}
};
Here we have added to the body of the loop a Thread.sleep
call. Since this is a blocking call, I have to handle the potential
InterruptedException. Within the catch block, I will check whether
the Task has been cancelled, and if so, update the message accordingly
and break out of the loop.
A Task Which Takes Parameters
Most Tasks require some parameters in order to do useful work. For
example, a DeleteRecordTask needs the object or primary key to delete
from the database. A ReadFileTask needs the URI of the file to be read.
Because Tasks operate on a background thread, care must be taken to
make sure the body of the call
method does not read or
modify any shared state. There are two techniques most useful for
doing this: using final variables, and passing variables to a Task
during construction.
When using a Task as an anonymous class, the most natural way to pass parameters to the Task is by using final variables. In this example, we pass to the Task the total number of times the Task should iterate.
final int totalIterations = 9000000;
Task<Integer> task = new Task<Integer>() {
@Override protected Integer call() throws Exception {
int iterations;
for (iterations = 0; iterations < totalIterations; iterations++) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
updateMessage("Iteration " + iterations);
updateProgress(iterations, totalIterations);
}
return iterations;
}
};
Since totalIterations
is final, the call
method can safely read it and refer to it from a background thread.
When writing Task libraries (as opposed to specific-use implementations), we need to use a different technique. In this case, I will create an IteratingTask which performs the same work as above. This time, since the IteratingTask is defined in its own file, it will need to have parameters passed to it in its constructor. These parameters are assigned to final variables.
public class IteratingTask extends Task<Integer> {
private final int totalIterations;
public IteratingTask(int totalIterations) {
this.totalIterations = totalIterations;
}
@Override protected Integer call() throws Exception {
int iterations = 0;
for (iterations = 0; iterations < totalIterations; iterations++) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
updateMessage("Iteration " + iterations);
updateProgress(iterations, totalIterations);
}
return iterations;
}
}
And then when used:
IteratingTask task = new IteratingTask(8000000);
In this way, parameters are passed to the IteratingTask in a safe
manner, and again, are final. Thus, the call
method can
safely read this state from a background thread.
WARNING: Do not pass mutable state to a Task and then operate on it from a background thread. Doing so may introduce race conditions. In particular, suppose you had a SaveCustomerTask which took a Customer in its constructor. Although the SaveCustomerTask may have a final reference to the Customer, if the Customer object is mutable, then it is possible that both the SaveCustomerTask and some other application code will be reading or modifying the state of the Customer from different threads. Be very careful in such cases, that while a mutable object such as this Customer is being used from a background thread, that it is not being used also from another thread. In particular, if the background thread is reading data from the database and updating the Customer object, and the Customer object is bound to scene graph nodes (such as UI controls), then there could be a violation of threading rules! For such cases, modify the Customer object from the FX Application Thread rather than from the background thread.
public class UpdateCustomerTask extends Task<Customer> {
private final Customer customer;
public UpdateCustomerTask(Customer customer) {
this.customer = customer;
}
@Override protected Customer call() throws Exception {
// pseudo-code:
// query the database
// read the values
// Now update the customer
Platform.runLater(new Runnable() {
@Override public void run() {
customer.setFirstName(rs.getString("FirstName"));
// etc
}
});
return customer;
}
}
A Task Which Returns No Value
Many, if not most, Tasks should return a value upon completion. For CRUD Tasks, one would expect that a "Create" Task would return the newly created object or primary key, a "Read" Task would return the read object, an "Update" task would return the number of records updated, and a "Delete" task would return the number of records deleted.
However sometimes there just isn't anything truly useful to return.
For example, I might have a Task which writes to a file. Task has built
into it a mechanism for indicating whether it has succeeded or failed
along with the number of bytes written (the progress), and thus there is
nothing really for me to return. In such a case, you can use the Void
type. This is a special type in the Java language which can only be
assigned the value of null
. You would use it as follows:
final String filePath = "/foo.txt";
final String contents = "Some contents";
Task<Void> task = new Task<Void>() {
@Override protected Void call() throws Exception {
File file = new File(filePath);
FileOutputStream out = new FileOutputStream(file);
// ... and other code to write the contents ...
// Return null at the end of a Task of type Void
return null;
}
};
A Task Which Returns An ObservableList
Because the ListView, TableView, and other UI controls and scene graph
nodes make use of ObservableList, it is common to want to create and return
an ObservableList from a Task. When you do not care to display intermediate
values, the easiest way to correctly write such a Task is simply to
construct an ObservableList within the call
method, and then
return it at the conclusion of the Task.
Task<ObservableList<Rectangle>> task = new Task<ObservableList<Rectangle>>() {
@Override protected ObservableList<Rectangle> call() throws Exception {
updateMessage("Creating Rectangles");
ObservableList<Rectangle> results = FXCollections.observableArrayList();
for (int i=0; i<100; i++) {
if (isCancelled()) break;
Rectangle r = new Rectangle(10, 10);
r.setX(10 * i);
results.add(r);
updateProgress(i, 100);
}
return results;
}
};
In the above example, we are going to create 100 rectangles and return
them from this task. An ObservableList is created within the
call
method, populated, and then returned.
A Task Which Returns Partial Results
Sometimes you want to create a Task which will return partial results. Perhaps you are building a complex scene graph and want to show the scene graph as it is being constructed. Or perhaps you are reading a large amount of data over the network and want to display the entries in a TableView as the data is arriving. In such cases, there is some shared state available both to the FX Application Thread and the background thread. Great care must be taken to never update shared state from any thread other than the FX Application Thread.
The easiest way to do this is to take advantage of the updateValue(Object)
method.
This method may be called repeatedly from the background thread. Updates are coalesced to
prevent saturation of the FX event queue. This means you can call it as frequently as
you like from the background thread but only the most recent set is ultimately set.
Task<Long> task = new Task<Long>() {
@Override protected Long call() throws Exception {
long a = 0;
long b = 1;
for (long i = 0; i < Long.MAX_VALUE; i++) {
updateValue(a);
a += b;
b = a - b;
}
return a;
}
};
Another way to do this is to expose a new property on the Task
which will represent the partial result. Then make sure to use
Platform.runLater
when updating the partial result.
Task<Long> task = new Task<Long>() {
@Override protected Long call() throws Exception {
long a = 0;
long b = 1;
for (long i = 0; i < Long.MAX_VALUE; i++) {
final long v = a;
Platform.runLater(new Runnable() {
@Override public void run() {
updateValue(v);
}
}
a += b;
b = a - b;
}
return a;
}
};
Suppose instead of updating a single value, you want to populate an ObservableList
with results as they are obtained. One approach is to expose a new property on the Task
which will represent the partial result. Then make sure to use
Platform.runLater
when adding new items to the partial
result.
public class PartialResultsTask extends Task<ObservableList<Rectangle>> {
// Uses Java 7 diamond operator
private ReadOnlyObjectWrapper<ObservableList<Rectangle>> partialResults =
new ReadOnlyObjectWrapper<>(this, "partialResults",
FXCollections.observableArrayList(new ArrayList<Rectangle>()));
public final ObservableList<Rectangle> getPartialResults() { return partialResults.get(); }
public final ReadOnlyObjectProperty<ObservableList<Rectangle>> partialResultsProperty() {
return partialResults.getReadOnlyProperty();
}
@Override protected ObservableList<Rectangle> call() throws Exception {
updateMessage("Creating Rectangles...");
for (int i=0; i<100; i++) {
if (isCancelled()) break;
final Rectangle r = new Rectangle(10, 10);
r.setX(10 * i);
Platform.runLater(new Runnable() {
@Override public void run() {
partialResults.get().add(r);
}
});
updateProgress(i, 100);
}
return partialResults.get();
}
}
A Task Which Modifies The Scene Graph
Generally, Tasks should not interact directly with the UI. Doing so
creates a tight coupling between a specific Task implementation and a
specific part of your UI. However, when you do want to create such a
coupling, you must ensure that you use Platform.runLater
so that any modifications of the scene graph occur on the
FX Application Thread.
final Group group = new Group();
Task<Void> task = new Task<Void>() {
@Override protected Void call() throws Exception {
for (int i=0; i<100; i++) {
if (isCancelled()) break;
final Rectangle r = new Rectangle(10, 10);
r.setX(10 * i);
Platform.runLater(new Runnable() {
@Override public void run() {
group.getChildren().add(r);
}
});
}
return null;
}
};
Reacting To State Changes Generically
Sometimes you may want to write a Task which updates its progress, message, text, or in some other way reacts whenever a state change happens on the Task. For example, you may want to change the status message on the Task on Failure, Success, Running, or Cancelled state changes.
Task<Integer> task = new Task<Integer>() {
@Override protected Integer call() throws Exception {
int iterations = 0;
for (iterations = 0; iterations < 100000; iterations++) {
if (isCancelled()) {
break;
}
System.out.println("Iteration " + iterations);
}
return iterations;
}
@Override protected void succeeded() {
super.succeeded();
updateMessage("Done!");
}
@Override protected void cancelled() {
super.cancelled();
updateMessage("Cancelled!");
}
@Override protected void failed() {
super.failed();
updateMessage("Failed!");
}
};
- Since:
- JavaFX 2.0
-
Property Summary
Properties Type Property Description ReadOnlyObjectProperty<Throwable>
exception
Gets the ReadOnlyObjectProperty representing any exception which occurred.ReadOnlyStringProperty
message
Gets the ReadOnlyStringProperty representing the message.ObjectProperty<EventHandler<WorkerStateEvent>>
onCancelled
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.ObjectProperty<EventHandler<WorkerStateEvent>>
onFailed
The onFailed event handler is called whenever the Task state transitions to the FAILED state.ObjectProperty<EventHandler<WorkerStateEvent>>
onRunning
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.ObjectProperty<EventHandler<WorkerStateEvent>>
onScheduled
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.ObjectProperty<EventHandler<WorkerStateEvent>>
onSucceeded
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.ReadOnlyDoubleProperty
progress
Gets the ReadOnlyDoubleProperty representing the progress.ReadOnlyBooleanProperty
running
Gets the ReadOnlyBooleanProperty representing whether the Worker is running.ReadOnlyObjectProperty<Worker.State>
state
Gets the ReadOnlyObjectProperty representing the current state.ReadOnlyStringProperty
title
Gets the ReadOnlyStringProperty representing the title.ReadOnlyDoubleProperty
totalWork
Gets the ReadOnlyDoubleProperty representing the maximum amount of work that needs to be done.ReadOnlyObjectProperty<V>
value
Gets the ReadOnlyObjectProperty representing the value.ReadOnlyDoubleProperty
workDone
Gets the ReadOnlyDoubleProperty representing the current progress. -
Nested Class Summary
Nested classes/interfaces inherited from interface javafx.concurrent.Worker
Worker.State
-
Constructor Summary
Constructors Constructor Description Task()
Creates a new Task. -
Method Summary
Modifier and Type Method Description <T extends Event>
voidaddEventFilter(EventType<T> eventType, EventHandler<? super T> eventFilter)
Registers an event filter to this task.<T extends Event>
voidaddEventHandler(EventType<T> eventType, EventHandler<? super T> eventHandler)
Registers an event handler to this task.EventDispatchChain
buildEventDispatchChain(EventDispatchChain tail)
Construct an event dispatch chain for this target.protected abstract V
call()
Invoked when the Task is executed, the call method must be overridden and implemented by subclasses.boolean
cancel()
Terminates execution of this Worker.boolean
cancel(boolean mayInterruptIfRunning)
protected void
cancelled()
A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the CANCELLED state.ReadOnlyObjectProperty<Throwable>
exceptionProperty()
Gets the ReadOnlyObjectProperty representing any exception which occurred.protected void
failed()
A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the FAILED state.void
fireEvent(Event event)
Fires the specified event.Throwable
getException()
Gets the value of the property exception.String
getMessage()
Gets the value of the property message.EventHandler<WorkerStateEvent>
getOnCancelled()
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.EventHandler<WorkerStateEvent>
getOnFailed()
The onFailed event handler is called whenever the Task state transitions to the FAILED state.EventHandler<WorkerStateEvent>
getOnRunning()
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.EventHandler<WorkerStateEvent>
getOnScheduled()
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.EventHandler<WorkerStateEvent>
getOnSucceeded()
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.double
getProgress()
Gets the value of the property progress.Worker.State
getState()
Gets the value of the property state.String
getTitle()
Gets the value of the property title.double
getTotalWork()
Gets the value of the property totalWork.V
getValue()
Gets the value of the property value.double
getWorkDone()
Gets the value of the property workDone.boolean
isRunning()
Gets the value of the property running.ReadOnlyStringProperty
messageProperty()
Gets the ReadOnlyStringProperty representing the message.ObjectProperty<EventHandler<WorkerStateEvent>>
onCancelledProperty()
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.ObjectProperty<EventHandler<WorkerStateEvent>>
onFailedProperty()
The onFailed event handler is called whenever the Task state transitions to the FAILED state.ObjectProperty<EventHandler<WorkerStateEvent>>
onRunningProperty()
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.ObjectProperty<EventHandler<WorkerStateEvent>>
onScheduledProperty()
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.ObjectProperty<EventHandler<WorkerStateEvent>>
onSucceededProperty()
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.ReadOnlyDoubleProperty
progressProperty()
Gets the ReadOnlyDoubleProperty representing the progress.<T extends Event>
voidremoveEventFilter(EventType<T> eventType, EventHandler<? super T> eventFilter)
Unregisters a previously registered event filter from this task.<T extends Event>
voidremoveEventHandler(EventType<T> eventType, EventHandler<? super T> eventHandler)
Unregisters a previously registered event handler from this task.protected void
running()
A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the RUNNING state.ReadOnlyBooleanProperty
runningProperty()
Gets the ReadOnlyBooleanProperty representing whether the Worker is running.protected void
scheduled()
A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the SCHEDULED state.protected <T extends Event>
voidsetEventHandler(EventType<T> eventType, EventHandler<? super T> eventHandler)
Sets the handler to use for this event type.void
setOnCancelled(EventHandler<WorkerStateEvent> value)
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.void
setOnFailed(EventHandler<WorkerStateEvent> value)
The onFailed event handler is called whenever the Task state transitions to the FAILED state.void
setOnRunning(EventHandler<WorkerStateEvent> value)
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.void
setOnScheduled(EventHandler<WorkerStateEvent> value)
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.void
setOnSucceeded(EventHandler<WorkerStateEvent> value)
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.ReadOnlyObjectProperty<Worker.State>
stateProperty()
Gets the ReadOnlyObjectProperty representing the current state.protected void
succeeded()
A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the SUCCEEDED state.ReadOnlyStringProperty
titleProperty()
Gets the ReadOnlyStringProperty representing the title.ReadOnlyDoubleProperty
totalWorkProperty()
Gets the ReadOnlyDoubleProperty representing the maximum amount of work that needs to be done.protected void
updateMessage(String message)
Updates themessage
property.protected void
updateProgress(double workDone, double max)
Updates theworkDone
,totalWork
, andprogress
properties.protected void
updateProgress(long workDone, long max)
Updates theworkDone
,totalWork
, andprogress
properties.protected void
updateTitle(String title)
Updates thetitle
property.protected void
updateValue(V value)
Updates thevalue
property.ReadOnlyObjectProperty<V>
valueProperty()
Gets the ReadOnlyObjectProperty representing the value.ReadOnlyDoubleProperty
workDoneProperty()
Gets the ReadOnlyDoubleProperty representing the current progress.Methods inherited from class java.util.concurrent.FutureTask
done, get, get, isCancelled, isDone, run, runAndReset, set, setException, toString
-
Property Details
-
state
- Specified by:
stateProperty
in interfaceWorker<V>
- See Also:
getState()
-
onScheduled
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.- Since:
- JavaFX 2.1
- See Also:
getOnScheduled()
,setOnScheduled(EventHandler)
-
onRunning
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.- Since:
- JavaFX 2.1
- See Also:
getOnRunning()
,setOnRunning(EventHandler)
-
onSucceeded
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.- Since:
- JavaFX 2.1
- See Also:
getOnSucceeded()
,setOnSucceeded(EventHandler)
-
onCancelled
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.- Since:
- JavaFX 2.1
- See Also:
getOnCancelled()
,setOnCancelled(EventHandler)
-
onFailed
The onFailed event handler is called whenever the Task state transitions to the FAILED state.- Since:
- JavaFX 2.1
- See Also:
getOnFailed()
,setOnFailed(EventHandler)
-
value
- Specified by:
valueProperty
in interfaceWorker<V>
- See Also:
getValue()
-
exception
- Specified by:
exceptionProperty
in interfaceWorker<V>
- See Also:
getException()
-
workDone
- Specified by:
workDoneProperty
in interfaceWorker<V>
- See Also:
getWorkDone()
-
totalWork
- Specified by:
totalWorkProperty
in interfaceWorker<V>
- See Also:
getTotalWork()
-
progress
- Specified by:
progressProperty
in interfaceWorker<V>
- See Also:
getProgress()
-
running
- Specified by:
runningProperty
in interfaceWorker<V>
- See Also:
isRunning()
-
message
- Specified by:
messageProperty
in interfaceWorker<V>
- See Also:
getMessage()
-
title
- Specified by:
titleProperty
in interfaceWorker<V>
- See Also:
getTitle()
-
-
Constructor Details
-
Task
public Task()Creates a new Task.
-
-
Method Details
-
call
Invoked when the Task is executed, the call method must be overridden and implemented by subclasses. The call method actually performs the background thread logic. Only the updateProgress, updateMessage, updateValue and updateTitle methods of Task may be called from code within this method. Any other interaction with the Task from the background thread will result in runtime exceptions.- Returns:
- The result of the background work, if any.
- Throws:
Exception
- an unhandled exception which occurred during the background operation
-
getState
Gets the value of the property state. -
stateProperty
Description copied from interface:Worker
Gets the ReadOnlyObjectProperty representing the current state.- Specified by:
stateProperty
in interfaceWorker<V>
- See Also:
getState()
-
onScheduledProperty
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.- Since:
- JavaFX 2.1
- See Also:
getOnScheduled()
,setOnScheduled(EventHandler)
-
getOnScheduled
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.- Returns:
- the onScheduled event handler, if any
- Since:
- JavaFX 2.1
-
setOnScheduled
The onSchedule event handler is called whenever the Task state transitions to the SCHEDULED state.- Parameters:
value
- the event handler, can be null to clear it- Since:
- JavaFX 2.1
-
scheduled
protected void scheduled()A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the SCHEDULED state. This method is invoked on the FX Application Thread after the Task has been fully transitioned to the new state.- Since:
- JavaFX 2.1
-
onRunningProperty
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.- Since:
- JavaFX 2.1
- See Also:
getOnRunning()
,setOnRunning(EventHandler)
-
getOnRunning
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.- Returns:
- the onRunning event handler, if any
- Since:
- JavaFX 2.1
-
setOnRunning
The onRunning event handler is called whenever the Task state transitions to the RUNNING state.- Parameters:
value
- the event handler, can be null to clear it- Since:
- JavaFX 2.1
-
running
protected void running()A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the RUNNING state. This method is invoked on the FX Application Thread after the Task has been fully transitioned to the new state.- Since:
- JavaFX 2.1
-
onSucceededProperty
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.- Since:
- JavaFX 2.1
- See Also:
getOnSucceeded()
,setOnSucceeded(EventHandler)
-
getOnSucceeded
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.- Returns:
- the onSucceeded event handler, if any
- Since:
- JavaFX 2.1
-
setOnSucceeded
The onSucceeded event handler is called whenever the Task state transitions to the SUCCEEDED state.- Parameters:
value
- the event handler, can be null to clear it- Since:
- JavaFX 2.1
-
succeeded
protected void succeeded()A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the SUCCEEDED state. This method is invoked on the FX Application Thread after the Task has been fully transitioned to the new state.- Since:
- JavaFX 2.1
-
onCancelledProperty
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.- Since:
- JavaFX 2.1
- See Also:
getOnCancelled()
,setOnCancelled(EventHandler)
-
getOnCancelled
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.- Returns:
- the onCancelled event handler, if any
- Since:
- JavaFX 2.1
-
setOnCancelled
The onCancelled event handler is called whenever the Task state transitions to the CANCELLED state.- Parameters:
value
- the event handler, can be null to clear it- Since:
- JavaFX 2.1
-
cancelled
protected void cancelled()A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the CANCELLED state. This method is invoked on the FX Application Thread after the Task has been fully transitioned to the new state.- Since:
- JavaFX 2.1
-
onFailedProperty
The onFailed event handler is called whenever the Task state transitions to the FAILED state.- Since:
- JavaFX 2.1
- See Also:
getOnFailed()
,setOnFailed(EventHandler)
-
getOnFailed
The onFailed event handler is called whenever the Task state transitions to the FAILED state.- Returns:
- the onFailed event handler, if any
- Since:
- JavaFX 2.1
-
setOnFailed
The onFailed event handler is called whenever the Task state transitions to the FAILED state.- Parameters:
value
- the event handler, can be null to clear it- Since:
- JavaFX 2.1
-
failed
protected void failed()A protected convenience method for subclasses, called whenever the state of the Task has transitioned to the FAILED state. This method is invoked on the FX Application Thread after the Task has been fully transitioned to the new state.- Since:
- JavaFX 2.1
-
getValue
Gets the value of the property value. -
valueProperty
Description copied from interface:Worker
Gets the ReadOnlyObjectProperty representing the value.- Specified by:
valueProperty
in interfaceWorker<V>
- See Also:
getValue()
-
getException
Gets the value of the property exception.- Specified by:
getException
in interfaceWorker<V>
- Property description:
- Returns:
- the exception, if one occurred
-
exceptionProperty
Description copied from interface:Worker
Gets the ReadOnlyObjectProperty representing any exception which occurred.- Specified by:
exceptionProperty
in interfaceWorker<V>
- See Also:
getException()
-
getWorkDone
public final double getWorkDone()Gets the value of the property workDone.- Specified by:
getWorkDone
in interfaceWorker<V>
- Property description:
- Returns:
- the amount of work done
- See Also:
Worker.totalWorkProperty()
,Worker.progressProperty()
-
workDoneProperty
Description copied from interface:Worker
Gets the ReadOnlyDoubleProperty representing the current progress.- Specified by:
workDoneProperty
in interfaceWorker<V>
- See Also:
getWorkDone()
-
getTotalWork
public final double getTotalWork()Gets the value of the property totalWork.- Specified by:
getTotalWork
in interfaceWorker<V>
- Property description:
- Returns:
- the total work to be done
- See Also:
Worker.workDoneProperty()
,Worker.progressProperty()
-
totalWorkProperty
Description copied from interface:Worker
Gets the ReadOnlyDoubleProperty representing the maximum amount of work that needs to be done. These "work units" have meaning to the Worker implementation, such as the number of bytes that need to be downloaded or the number of images to process or some other such metric.- Specified by:
totalWorkProperty
in interfaceWorker<V>
- See Also:
getTotalWork()
-
getProgress
public final double getProgress()Gets the value of the property progress.- Specified by:
getProgress
in interfaceWorker<V>
- Property description:
- Returns:
- the current progress
- See Also:
Worker.workDoneProperty()
,Worker.totalWorkProperty()
-
progressProperty
Description copied from interface:Worker
Gets the ReadOnlyDoubleProperty representing the progress.- Specified by:
progressProperty
in interfaceWorker<V>
- See Also:
getProgress()
-
isRunning
public final boolean isRunning()Gets the value of the property running. -
runningProperty
Description copied from interface:Worker
Gets the ReadOnlyBooleanProperty representing whether the Worker is running.- Specified by:
runningProperty
in interfaceWorker<V>
- See Also:
isRunning()
-
getMessage
Gets the value of the property message.- Specified by:
getMessage
in interfaceWorker<V>
- Property description:
- Returns:
- the current message
-
messageProperty
Description copied from interface:Worker
Gets the ReadOnlyStringProperty representing the message.- Specified by:
messageProperty
in interfaceWorker<V>
- See Also:
getMessage()
-
getTitle
Gets the value of the property title. -
titleProperty
Description copied from interface:Worker
Gets the ReadOnlyStringProperty representing the title.- Specified by:
titleProperty
in interfaceWorker<V>
- See Also:
getTitle()
-
cancel
public final boolean cancel()Description copied from interface:Worker
Terminates execution of this Worker. Calling this method will either remove this Worker from the execution queue or stop execution. -
cancel
public boolean cancel(boolean mayInterruptIfRunning) -
updateProgress
protected void updateProgress(long workDone, long max)Updates theworkDone
,totalWork
, andprogress
properties. Calls to updateProgress are coalesced and run later on the FX application thread, and calls to updateProgress, even from the FX Application thread, may not necessarily result in immediate updates to these properties, and intermediate workDone values may be coalesced to save on event notifications.max
becomes the new value fortotalWork
.This method is safe to be called from any thread.
- Parameters:
workDone
- A value from Long.MIN_VALUE up to max. If the value is greater than max, then it will be clamped at max. If the value passed is negative then the resulting percent done will be -1 (thus, indeterminate).max
- A value from Long.MIN_VALUE to Long.MAX_VALUE.- See Also:
updateProgress(double, double)
-
updateProgress
protected void updateProgress(double workDone, double max)Updates theworkDone
,totalWork
, andprogress
properties. Calls to updateProgress are coalesced and run later on the FX application thread, and calls to updateProgress, even from the FX Application thread, may not necessarily result in immediate updates to these properties, and intermediate workDone values may be coalesced to save on event notifications.max
becomes the new value fortotalWork
.This method is safe to be called from any thread.
- Parameters:
workDone
- A value from Double.MIN_VALUE up to max. If the value is greater than max, then it will be clamped at max. If the value passed is negative, or Infinity, or NaN, then the resulting percentDone will be -1 (thus, indeterminate).max
- A value from Double.MIN_VALUE to Double.MAX_VALUE. Infinity and NaN are treated as -1.- Since:
- JavaFX 2.2
-
updateMessage
Updates themessage
property. Calls to updateMessage are coalesced and run later on the FX application thread, so calls to updateMessage, even from the FX Application thread, may not necessarily result in immediate updates to this property, and intermediate message values may be coalesced to save on event notifications.This method is safe to be called from any thread.
- Parameters:
message
- the new message
-
updateTitle
Updates thetitle
property. Calls to updateTitle are coalesced and run later on the FX application thread, so calls to updateTitle, even from the FX Application thread, may not necessarily result in immediate updates to this property, and intermediate title values may be coalesced to save on event notifications.This method is safe to be called from any thread.
- Parameters:
title
- the new title
-
updateValue
Updates thevalue
property. Calls to updateValue are coalesced and run later on the FX application thread, so calls to updateValue, even from the FX Application thread, may not necessarily result in immediate updates to this property, and intermediate values may be coalesced to save on event notifications.This method is safe to be called from any thread.
- Parameters:
value
- the new value- Since:
- JavaFX 8.0
-
addEventHandler
public final <T extends Event> void addEventHandler(EventType<T> eventType, EventHandler<? super T> eventHandler)Registers an event handler to this task. Any event filters are first processed, then the specified onFoo event handlers, and finally any event handlers registered by this method. As with other events in the scene graph, if an event is consumed, it will not continue dispatching.- Type Parameters:
T
- the specific event class of the handler- Parameters:
eventType
- the type of the events to receive by the handlereventHandler
- the handler to register- Throws:
NullPointerException
- if the event type or handler is null- Since:
- JavaFX 2.1
-
removeEventHandler
public final <T extends Event> void removeEventHandler(EventType<T> eventType, EventHandler<? super T> eventHandler)Unregisters a previously registered event handler from this task. One handler might have been registered for different event types, so the caller needs to specify the particular event type from which to unregister the handler.- Type Parameters:
T
- the specific event class of the handler- Parameters:
eventType
- the event type from which to unregistereventHandler
- the handler to unregister- Throws:
NullPointerException
- if the event type or handler is null- Since:
- JavaFX 2.1
-
addEventFilter
public final <T extends Event> void addEventFilter(EventType<T> eventType, EventHandler<? super T> eventFilter)Registers an event filter to this task. Registered event filters get an event before any associated event handlers.- Type Parameters:
T
- the specific event class of the filter- Parameters:
eventType
- the type of the events to receive by the filtereventFilter
- the filter to register- Throws:
NullPointerException
- if the event type or filter is null- Since:
- JavaFX 2.1
-
removeEventFilter
public final <T extends Event> void removeEventFilter(EventType<T> eventType, EventHandler<? super T> eventFilter)Unregisters a previously registered event filter from this task. One filter might have been registered for different event types, so the caller needs to specify the particular event type from which to unregister the filter.- Type Parameters:
T
- the specific event class of the filter- Parameters:
eventType
- the event type from which to unregistereventFilter
- the filter to unregister- Throws:
NullPointerException
- if the event type or filter is null- Since:
- JavaFX 2.1
-
setEventHandler
protected final <T extends Event> void setEventHandler(EventType<T> eventType, EventHandler<? super T> eventHandler)Sets the handler to use for this event type. There can only be one such handler specified at a time. This handler is guaranteed to be called first. This is used for registering the user-defined onFoo event handlers.- Type Parameters:
T
- the specific event class of the handler- Parameters:
eventType
- the event type to associate with the given eventHandlereventHandler
- the handler to register, or null to unregister- Throws:
NullPointerException
- if the event type is null- Since:
- JavaFX 2.1
-
fireEvent
Fires the specified event. Any event filter encountered will be notified and can consume the event. If not consumed by the filters, the event handlers on this task are notified. If these don't consume the event either, then all event handlers are called and can consume the event.This method must be called on the FX user thread.
- Parameters:
event
- the event to fire- Since:
- JavaFX 2.1
-
buildEventDispatchChain
Description copied from interface:EventTarget
Construct an event dispatch chain for this target. The event dispatch chain contains event dispatchers which might be interested in processing of events targeted at thisEventTarget
. This event target is not automatically added to the chain, so if it wants to process events, it needs to add anEventDispatcher
for itself to the chain.In the case the event target is part of some hierarchy, the chain for it is usually built from event dispatchers collected from the root of the hierarchy to the event target.
The event dispatch chain is constructed by modifications to the provided initial event dispatch chain. The returned chain should have the initial chain at its end so the dispatchers should be prepended to the initial chain.
The caller shouldn't assume that the initial chain remains unchanged nor that the returned value will reference a different chain.
- Specified by:
buildEventDispatchChain
in interfaceEventTarget
- Parameters:
tail
- the initial chain to build from- Returns:
- the resulting event dispatch chain for this target
-