Concurrency Utilities for Java EE is being worked as JSR 236 and has released an Early Draft. It provides concurrency capabilities to Java EE application components without compromising container integrity. Simple (common) and advanced concurrency patterns are easily supported without sacrificing usability.

Using Java SE concurrency utilities such as java.util.concurrent API, java.lang.Thread and java.util.Timer in a Java EE application component such as EJB or Servlet are problematic since the container and server have no knowledge of these resources. JSR 236 enables concurrency largely by extending the Concurrency Utilities API developed under JSR-166. This also allows a consistency between Java SE and Java EE concurrency programming model.

There are four main programming interfaces available:

• ManagedExecutorService
• ManagedScheduledExecutorService
• ContextService
• ManagedThreadFactory

ManagedExecutorService is a managed version of java.util.concurrent.ExecutorService. The implementations of this interface are provided by the container and accessible using JNDI reference:

<resource-env-ref>
  <resource-env-ref-name>
    concurrent/BatchExecutor
  </resource-env-ref-name>
  <resource-env-ref-type>
    javax.enterprise.concurrent.ManagedExecutorService
  </resource-env-ref-type>
<resource-env-ref>

and available as:

@Resource(name="concurrent/BatchExecutor")
ManagedExecutorService executor;

Its recommended to bind the JNDI references in the java:comp/env/concurrent subcontext.

The asynchronous tasks that need to be executed need to implement java.lang.Runnable or java.util.concurrent.Callable interface as:

public class MyTask implements Runnable {
 public void run() {
 // business logic goes here
 }
}

OR

public class MyTask2 implements Callable<Date> {
  public Date call() {
 // business logic goes here 
  }
}

The task is then submitted to the executor using one of the submit method that return a Future instance. The Future represents the result of the task and can also be used to check if the task is complete or wait for its completion.

Future<String> future = executor.submit(new MyTask(), String.class);
. . .
String result = future.get();

Another example to submit tasks is:

class MyTask implements Callback<Long> { . . . }
class MyTask2 implements Callback<Date> { . . . }

ArrayList<Callable> tasks = new ArrayList<();
tasks.add(new MyTask());
tasks.add(new MyTask2());
List<Future<Object>> result = executor.invokeAll(tasks);

The ManagedExecutorService may be configured for different properties such as:

• Hung Task Threshold: Time in milliseconds that a task can execute before it is considered hung
• Pool Info
• Core Size: Number of threads to keep alive
• Maximum Size: Maximum number of threads allowed in the pool
• Keep Alive: Time to allow threads to remain idle when # of threads > Core Size
• Work Queue Capacity: # of tasks that can be stored in inbound buffer
  
• Thread Use: Application intend to run short vs long-running tasks, accordingly pooled or daemon threads are picked
  

ManagedScheduledExecutorService adds delay and periodic task running capabilities to ManagedExecutorService. The implementations of this interface are provided by the container and accessible using JNDI reference:

<resource-env-ref>
  <resource-env-ref-name>
    concurrent/BatchExecutor
  </resource-env-ref-name>
  <resource-env-ref-type>
    javax.enterprise.concurrent.ManagedExecutorService
  </resource-env-ref-type>
<resource-env-ref>

and available as:

@Resource(name="concurrent/timedExecutor")
ManagedExecutorService executor;

And then the tasks are submitted using submit, invokeXXX or scheduleXXX methods.

ScheduledFuture<?> future = executor.schedule(new MyTask(), 5, TimeUnit.SECONDS);

This will create and execute a one-shot action that becomes enabled after 5 seconds of delay.

More control is possible using one of the newly added methods:

MyTaskListener implements ManagedTaskListener {
  public void taskStarting(...) { . . . }
  public void taskSubmitted(...) { . . . }
  public void taskDone(...) { . . . }
  public void taskAborted(...) { . . . }
}
ScheduledFuture<?> future = executor.schedule(new MyTask(), 5, TimeUnit.SECONDS, new MyTaskListener());

Here, ManagedTaskListener is used to monitor the state of a task's future.

ManagedThreadFactory provides a method for creating threads for execution in a managed environment. A simple usage is:

@Resource(name="concurrent/myThreadFactory")
ManagedThreadFactory factory;
. . .
Thread thread = factory.newThread(new Runnable() { . . . });

concurrent/myThreadFactory is a JNDI resource.

There is lot of interesting content in the Early Draft, download it, and read yourself. The implementation will be made available soon and also be integrated in GlassFish 4 as well.

Some references for further exploring ...

• Javadoc
• Early Draft Specification
  
• concurrency-ee-spec.java.net
• [email protected]