CallableBackgroundInitializer

public class org.apache.commons.lang3.concurrent.CallableBackgroundInitializer<T> extends BackgroundInitializer<T>

A specialized BackgroundInitializer implementation that wraps a Callable object.

An instance of this class is initialized with a Callable object when it is constructed. The implementation of the #initialize() method defined in the super class delegates to this Callable so that the Callable is executed in the background thread.

The java.util.concurrent.Callable interface is a standard mechanism of the JDK to define tasks to be executed by another thread. The CallableBackgroundInitializer class allows combining this standard interface with the background initializer API.

Usage of this class is very similar to the default usage pattern of the BackgroundInitializer class: Just create an instance and provide the Callable object to be executed, then call the initializer’s #start() method. This causes the Callable to be executed in another thread. When the results of the Callable are needed the initializer’s #get() method can be called (which may block until background execution is complete). The following code fragment shows a typical usage example:

// a Callable that performs a complex computation
Callable<Integer> computationCallable = new MyComputationCallable();
// setup the background initializer
CallableBackgroundInitializer<Integer> initializer =
    new CallableBackgroundInitializer(computationCallable);
initializer.start();
// Now do some other things. Initialization runs in a parallel thread
...
// Wait for the end of initialization and access the result
Integer result = initializer.get();

Parameters:

<T> – The type of the object managed by this initializer class

Since:

3.0

Constructors

CallableBackgroundInitializer(Callable)	Creates a new instance of CallableBackgroundInitializer and sets the Callable to be executed in a background thread.
CallableBackgroundInitializer(Callable, ExecutorService)	Creates a new instance of CallableBackgroundInitializer and initializes it with the Callable to be executed in a background thread and the ExecutorService for managing the background execution.

public CallableBackgroundInitializer(Callable<T> call)

Creates a new instance of CallableBackgroundInitializer and sets the Callable to be executed in a background thread.

Parameters:

call – The Callable (must not be null).

Throws:

java.lang.IllegalArgumentException – Thrown if the Callable is null.

public CallableBackgroundInitializer(Callable<T> call, ExecutorService exec)

Creates a new instance of CallableBackgroundInitializer and initializes it with the Callable to be executed in a background thread and the ExecutorService for managing the background execution.

Parameters:

• call – The Callable (must not be null).

• exec – An external ExecutorService to be used for task execution.

Throws:

java.lang.IllegalArgumentException – Thrown if the Callable is null.

Methods

getTypedException(Exception)	Gets an Exception with a type of E as defined by a concrete subclass of this class.
initialize()	Performs initialization in a background thread.

@Override protected Exception getTypedException(Exception e)

Gets an Exception with a type of E as defined by a concrete subclass of this class.

Parameters:

e – The actual exception that was thrown.

Returns:

A new exception with the actual type of E, that wraps e.

@Override protected T initialize() throws Exception

Performs initialization in a background thread. This implementation delegates to the Callable passed at construction time of this object.

Returns:

The result of the initialization.

Throws:

java.lang.Exception – Thrown if an error occurs.