Using JMX with Enterprise JavaBeans - JMX in Action - page 336

In the previous chapter, you learned about using JMX with the Java Message Ser-
vice ( JMS ), one of the components of the J2EE platform. In this chapter, you will
learn about using JMX with Enterprise JavaBeans ( EJB ), a technology that enables
you to access and manipulate enterprise data.
When people speak of J2EE , Enterprise JavaBeans immediately come to mind,
because EJB s are the most robust, scalable way to create enterprise applications.
However, like other applications, EJB applications can suffer from a lack of man-
agement and inability to be configured at runtime. Without additional custom
development, EJB applications often cannot easily provide a high level of obser-
vation and modification at runtime.
By combining JMX with your EJB s, you can provide a distributed, simple way to
gather information about, alter the behavior of, and monitor your enterprise appli-
cations. Using JMX , you can easily tap into the functionality of an EJB ; in return for
a little additional work, you gain significant advantages. As in chapter 13, which
demonstrated this same advantage by using JMX with JMS , you can use JMX to
open a window into the enterprise application.
Note that this chapter won't help you understand EJB s completely if you don't
already have some exposure to them. For more information about EJB s, go to
http://www.javasoft.com.

14.1 An EJB review

As we just stated, this chapter isn't an EJB tutorial. However, before diving into
working with EJB s and JMX , we do need to review a little information about EJB s.
If you have no experience with EJB s, we suggest you check out some of the docu-
mentation at http://www.javasoft.com.

14.1.1 The EJB model

As we've mentioned, EJB s are an ideal way for applications to access enterprise
data. The EJB specification defines a pattern for creating EJB s such that they can
be deployed in different containers without any code modification. The EJB con-
tainer provides services such as database persistence and an execution JVM . To
contain the EJB s in this chapter, you will again be using JBoss.
The EJB specification currently defines three types of EJB s: session beans,
entity beans, and message-driven beans. Each type of EJB gives you different
capabilities for reading or manipulating data.