Package com.luciad.fusion.util

Interface ILfnCallback<R>

Type Parameters:
R - the type of the result produced by the asynchronous task for which this callback was registered. Types which do not produce any result should use the Void type.
All Known Subinterfaces:
ILfnProgressCallback<R>, ILfnReadCallback
public interface ILfnCallback<R>
Interface to be implemented by objects interested in the result of an (asynchronously) executed task.

Tasks which are executed asynchronously usually offer two mechanisms for accessing their results: a future-based mechanism and a callback-based mechanism:

  • The future-based mechanism allows to poll for the status of the task (using the Future.isDone() method), and to retrieve the result via a blocking call on the future (Future.get()).
  • The callback-based mechanism allows to get notified of the result via the callback methods of ILfnCallback. A callback implementing this interface is therefore provided to the executor of the task.

Both mechanisms are usually provided at the same time, by API methods that look like: 


   Future<T> executeTask(Object aTaskParameter1, ..., ILfnCallback<T> aCallback);
where T is the type of the result produced by the asynchronous task. The callback is often allowed to be null, if one is only interested in the future.

Since callback methods may be invoked from any thread (asynchronously), implementations should take the necessary measures to ensure thread-safety. Especially updating the user interface directly from within these methods is not allowed, as user interface interactions should always be performed from within the Event Dispatch Thread.

The callback argument in asynchronous operations is usually the last parameter. This parameter may be null, meaning the caller is not interested in the asynchronous behavior. Asynchronous operations can easily be used in a synchronous workflow by using the Future's blocking "get" family of methods instead of the callback. This paradigm is illustrated in the code snippet below: 


 T result = executeTask(taskParameter1, ..., null).get();

Since:
2012.0

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    completed(R aResult)
    Called by the executor of the asynchronous task when the task has completed successfully.
    void
    threw(Throwable aThrowable)
    Called by the executor of the asynchronous task when the task failed to complete normally due to an error, exception or cancellation of the task.

  • Method Details

    • completed

      void completed(R aResult)
      Called by the executor of the asynchronous task when the task has completed successfully.
      Parameters:
      aResult - the result of the asynchronous task, or null for tasks that do not produce any result

    • threw

      void threw(Throwable aThrowable)
      Called by the executor of the asynchronous task when the task failed to complete normally due to an error, exception or cancellation of the task. In case of cancellation of the task (typically by calling Future.cancel()), a CancellationException will be reported on this method.
      Parameters:
      aThrowable - the error or exception causing the abortion of the task