10.1 Java 2 Enterprise Edition

Previous chapters have concentrated on describing JMX ^[1] as it is generally defined in the base specification: a framework suitable to instrument and manage any software application. The managed application can be a cell phone network, an office suite, an operating system component ”any program that can be represented as a collection of JMX MBeans. In fact, it is quite possible that the Java Virtual Machine itself will include a JMX agent as a standard component in one of the next revisions.

This chapter describes how JMX is used for management of a specific class of programs that are becoming more and more essential in the universe of the Internet and e-business. These classes of programs are called application servers. Although there are several forms of application servers, the most rapidly growing segment of this market consists of application servers that conform to the Java 2 Enterprise Edition (J2EE) ^[2] specification.

There are several books that cover all of the details incorporated in J2EE and how to create applications that can be served by compliant application server programs. We won't attempt to duplicate all of that information in this book, but it is important to present a basic overview of J2EE before discussing how JMX will be used to manage J2EE application servers.

From its beginning, the cross-platform portability of Java ^[3] has made it an attractive language for developers of applications that had to be usable in an "enterprise" environment. Such environments frequently have been built up by the combination of many heterogeneous computer networks consisting of a variety of computing platforms. The ubiquity of the Java Virtual Machine (JVM) hides a lot of the difficult system-level code details from the application developers and allows them to concentrate on creating the business logic for the application.

Even though the Java language itself became a de facto industry standard, there were many different extension libraries for building the distributed systems used in an enterprise environment. The Java 2 Enterprise Edition specification began as an effort to provide a unified, standard definition of the distributed services needed in this environment, as well as a component model for building applications for such an environment. J2EE has become a kind of umbrella specification that incorporates a whole series of subspecifications. The specification starts with the base Java 2 Standard Edition (J2SE) ^[4] and builds on top of that by adding extension libraries that must be supplied and supported by any compliant application server vendor. Some of the better-known parts of the J2EE specification include Enterprise JavaBeans (EJB), ^[5] servlets and JavaServer Pages (JSP), ^[6] Java DataBase Connectivity (JDBC), ^[7] and Java Message Service (JMS). ^[8]

Many products on the market comply with the J2EE specification. J2EE application servers must pass an extensive suite of compliance tests (the J2EE Compatibility Test Suite, or CTS) and are then officially designated to conform to J2EE. This means that applications designed to execute in one of these products can be easily deployed in a competing J2EE-compliant application server. Application portability between server products keeps the market competitive and puts the power of choice in the customer's hands, where it belongs (at least according to the widely held philosophy that has been part of the Java revolution since its beginnings).