Enterprise JavaBeans 3.1, 6th Edition

Asynchronous Methods

New in the EJB 3.1 Specification is the feature of fire-and-forget invocations upon session beans. Often we’ll have requirements where a request may take some time to be fully processed, and the client may not need to wait for the result or confirmation of completion. In these cases, we can take advantage of the new @javax.ejb.Asynchronous annotation to return control to the client before EJB is invoked. When the client does need access to the return value, it can do so via the facilities provided by java.util.concurrent.Future.

In the case of our EncryptionEJB, perhaps we have a very intensive hashing function that takes some time to complete:

    /**
     * Returns a one-way hash of the specified argument, calculated
asynchronously.
     * Useful for safely storing passwords.
     *
     * @param input
     * @return
     * @throws IllegalArgumentException
     * @throws EncryptionException
     */
    Future<String> hashAsync(String input) throws
IllegalArgumentException, EncryptionException;

During implementation, the bean provider may mark this method (either on the business interface or the bean class) as @Asynchronous, wrapping the real return value in a convenience implementation of java.util.concurrent.Future called javax.ejb.AsyncResult:

    @Asynchronous
    @Override
    public Future<String> hashAsync(final String input) throws
IllegalArgumentException, EncryptionException
    {
       // Get the real hash
       final String hash = this.hash(input);

       // Wrap and return
       return new AsyncResult<String>(hash);
    }

Client usage therefore ...