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EJB Timers are transactional objects. If the transaction that a timer is triggered under rolls back for some reason (e.g., as a result of a runtime exception in the timeout method), the timer creation is undone. In addition, the timeout method can be executed in a transactional context. You can specify a transactional attribute for the timeout method Required or RequiresNew and the container will start a transaction before invoking the timeout method. If the transaction fails, the container will make sure the changes made by the failed method do not take effect and will retry the timeout method. We ll talk about EJB transactions in much greater detail in the next chapter.

AspectJ is a compile-time weaver (since version 12, AspectJ can also weave aspect at loadtime) The aspect and class input files are woven together by AspectJ to produce a final application This application can then be executed as a regular Java application To compile the aspect with the three classes of the order-management application, call the ajc compiler from the operating-system command shell with the following command: ajc TraceAspectaj *java This command produces a set of class files that contain the bytecode of the aspectized application The first versions of AspectJ produced Java code The output of the ajc compiler was a Java program in which instructions from aspects and classes were merged This Java code could then be compiled by the regular javac Java compiler.

Clearly, although EJB timers are relatively feature-rich, they are not intended to go toe-to-toe against full-fledged scheduling solutions like Flux or Quartz. However, under some circumstances they are sufficient if not ideal. Like almost all other technology choices, this decision comes down to weighing features against needs for your specific situation and environment. Merits of timers Here are some of the merits of using EJB 3 timers:

By retrieving a serialized EJB handle, you can re-create the bean that was originally created and that produced the handle (see listing 1.13).

Timers are part of the EJB specification. Hence, applications using EJB timers will remain portable across containers instead of being locked into the nonstandard APIs of job schedulers like Quartz. Since the EJB timer service comes as a standard part of a Java EE application server, using it incurs no additional cost in terms of time or money. No extra installation or configuration is required as would be the case for an external job scheduler, and you won t need to worry about integration and support. The timer is a container-managed service. No separate thread pools or user threads are required for it, as would be the case with an external scheduler. For the same reasons, the EJB timer service is likely to have better out-of-the-box performance than third-party products. Transactions are fully supported with timers (see the sidebar titled EJB timers and transactions ), unlike external job schedulers, in which you may need to do extra setup for supporting JTA. By default, EJB timers are persisted and survive EJB lifecycles and container restarts. The same cannot be said of all third-party schedulers.

Limitations for timers The following are the primary limitations of EJB timers:

The advantage of this approach was that the produced code could easily be read by developers, who could then study the way that the pointcuts and advice code blocks were implemented Despite these benefits, this approach had several drawbacks The first had to do with performance The initial translation from Java to Java was costly In addition, a syntax analysis of the Java code was needed before the result of the weaving could be generated and writing a Java syntax analyzer that is fast enough to manage huge amounts of code is a difficult task Even more, this task is redundant with the one performed when the produced code is compiled The second disadvantage had to do with the source code needed to perform the weaving In some cases, the application was commercial or came from a developer who did not release the source code.