O'Reilly - Java Message Service
O'Reilly - Java Message Service
O'Reilly - Java Message Service
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Chapter 8. J2EE, EJB, and JMS<br />
8.1 J2EE Overview<br />
<strong>Java</strong> <strong>Message</strong> <strong>Service</strong><br />
<strong>Java</strong> 2, Enterprise Edition ( J2EE) is a specification that unites several other <strong>Java</strong><br />
enterprise technologies, including JMS, into one complete platform. J2EE is built on three<br />
main components: Enterprise <strong>Java</strong>Beans, Servlets, and <strong>Java</strong>Server Pages ( JSP). Many<br />
other technologies, such as JMS, JDBC, <strong>Java</strong>Mail, JTA, CORBA, and JNDI. are also<br />
included as services in J2EE. The <strong>Java</strong> <strong>Message</strong> <strong>Service</strong> actually has two roles in J2EE: it<br />
is both a service and the basis for a new enterprise bean type.<br />
To get a better understanding of what J2EE is, and why it is important, we need to discuss<br />
the three main components and explain how they are drawn together to form the unified<br />
J2EE platform. It is important to keep in mind that all the technologies discussed here are<br />
paper specifications licensed and implemented by vendors - a central theme in Sun<br />
Microsystems' enterprise technologies.<br />
8.1.1 Enterprise <strong>Java</strong>Beans<br />
Enterprise <strong>Java</strong>Beans (EJB) 2.0 defines a <strong>Java</strong> component model for component<br />
transaction monitors (CTMs). A CTM is a marriage of two technologies: distributed<br />
objects and transaction processing monitors (TPMs). Distributed object technologies such<br />
as CORBA, <strong>Java</strong> RMI-JRMP, and DCOM provide a networking and routing infrastructure<br />
that allows applications to access objects hosted on other processes or computers. A TPM,<br />
such as CICS or TUXEDO, provides a robust, secure, and scalable environment for<br />
running transactional applications. A CTM combines these technologies into transactional<br />
distributed objects that run in a robust, secure, and scalable environment. There are three<br />
main CTM technologies today: Sun's Enterprise <strong>Java</strong>Beans, Microsoft's COM+ (a.k.a.<br />
MTS), and the Object Management Group's CORBA Component Model (CCM). J2EE is<br />
built on EJB, which provides it with powerful transactional components that can be used to<br />
model and run an organization's business logic.<br />
Enterprise <strong>Java</strong>Beans are not at all like <strong>Java</strong> Beans. Enterprise<br />
<strong>Java</strong>Beans are nonvisual components that run on an application<br />
server. <strong>Java</strong> beans are used as visual widgets (buttons, graphs, etc.).<br />
Other than the common name "Bean" and the fact that they are both<br />
<strong>Java</strong> component technologies from Sun Microsystems, EJB and <strong>Java</strong><br />
Beans have very little in common.<br />
In Enterprise <strong>Java</strong>Beans 2.0, bean components come in three main flavors: session, entity,<br />
and message-driven beans. Session beans model processes and act as server-side<br />
extensions of their clients (they can manage a client's session state). Entity beans model<br />
persistent business objects; and combine business logic and database data. <strong>Message</strong>-driven<br />
beans, the newest bean type, are JMS clients that can consume messages concurrently in a<br />
robust and scalable EJB environment. The EJB 2.0 bean components are shown in Figure<br />
8.1.<br />
122
Change language