org.apache.commons.lang3.concurrent

Class CallableBackgroundInitializer<T>

java.lang.Object

org.apache.commons.lang3.concurrent.BackgroundInitializer<T>

org.apache.commons.lang3.concurrent.CallableBackgroundInitializer<T>

Type Parameters:

T - the type of the object managed by this initializer class

All Implemented Interfaces:

ConcurrentInitializer<T>

public class 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 BackgroundInitializer.start() method. This causes the Callable to be executed in another thread. When the results of the Callable are needed the initializer's BackgroundInitializer.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();
 

Since:

3.0

Constructor Summary

Constructors

Constructor and Description
CallableBackgroundInitializer(Callable<T> call) Creates a new instance of CallableBackgroundInitializer and sets the Callable to be executed in a background thread.
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.

Method Summary

Modifier and Type	Method and Description
protected T	initialize() Performs initialization in a background thread.

Methods inherited from class org.apache.commons.lang3.concurrent.BackgroundInitializer

get, getActiveExecutor, getExternalExecutor, getFuture, getTaskCount, isStarted, setExternalExecutor, start

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CallableBackgroundInitializer

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:

IllegalArgumentException - if the Callable is null

CallableBackgroundInitializer

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:

IllegalArgumentException - if the Callable is null

Method Detail

initialize

protected T initialize()
                throws Exception

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

Specified by:

initialize in class BackgroundInitializer<T>

Returns:

the result of the initialization

Throws:

Exception - if an error occurs