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. The 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. The threads so spawned are provided
and managed by the container.There are four main programming interfaces available:
ManagedExecutorServiceManagedScheduledExecutorServiceContextServiceManagedThreadFactory
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 implementjava.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();
The task would run on a separate thread provided and managed by the container.
Another example to submit tasks is:
class MyTask implements Callable<Long> { . . . }
class MyTask2 implements Callable<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
The specification does not mandate any configuration attributes.
The above mentioned properties are only examples and may not be
supported by all application servers.
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 exploration ...