Java Reference
In-Depth Information
Java SE
In the Java SE landscape, a myriad of options have been introduced over the years. First, there's the
standard java.lang.Thread support present since day 1 and Java Development Kit (JDK) 1.0. Java 1.3
saw the introduction of java.util.TimerTask to support doing some sort of work periodically. Java 5
debuted the java.util.concurrent package as well as a reworked hierarchy for building thread pools,
oriented around the java.util.concurrent.Executor .
The application programming interface (API) for Executor is simple:
package java.util.concurrent;
public interface Executor {
void execute(Runnable command);
ExecutorService , a subinterface, provides more functionality for managing threads and providing
support for raising events to the threads, such as shutdown() . There are several implementations that
have shipped with the JDK since Java SE 5.0. Many of them are available via static factory methods on
the java.util.concurrent.Executors class, in much the same way that utility methods for manipulating
java.util.Collection instances are offered on the java.util.Collections class. What follows are
examples. ExecutorService also provides a submit() method, which returns a Future<T> . An instance of
Future<T> can be used to track the progress of a thread that's executing—usually asynchronously. You
can call isDone() or isCancelled() to determine whether the job is finished or cancelled, respectively. If
you submit an object of type Runnable , whose primary method ( run ) supports no return type, the get()
on Future<T> method will return either null or a value that you specify as a parameter on submission of
the job, like so:
Runnable task = new Runnable(){
public void run(){
Thread.sleep( 1000 * 60 ) ;
System.out.println("Done sleeping for a minute, returning! " );
ExecutorService executorService = Executors.newCachedThreadPool() ;
if(executorService.submit(task, Boolean.TRUE).get().equals( Boolean.TRUE ))
System.out.println( "Job has finished!");
With that in hand, you can explore some the characteristics of the various implementations. For
example, you'll use the following Runnable instance:
package com.apress.springenterpriserecipes.spring3.executors;
import java.util.Date;
import org.apache.commons.lang.exception.ExceptionUtils;
public class DemonstrationRunnable implements Runnable {
public void run() {
try {
} catch (InterruptedException e) {
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