Chapter 6: Applying J2EE Technologies

Overview

In this chapter we'll take a deeper look at some of the key decisions involved in developing a J2EE architecture, especially those we discussed in Chapter 1. We'll discuss:

• Choosing between a collocated and distributed architecture
  This is a particularly important decision with implications for performance, ease of implementation, scalability, robustness and the type of clients that an application can support. This decision should be made early in the design process, as it has implications for many other design decisions.

• Choosing if and how to use EJB
  As we saw in Chapter 1, EJB is a powerful technology that can help us solve some complex problems, but which may introduce unwarranted complexity if we don't need its full capabilities. In this chapter, we'll take a closer look at when, and how, to use EJB to enjoy its benefits but avoid its drawbacks.

• Choosing when to use messaging
  Sometimes business requirements call for asynchronous application behavior or the use of messaging to communicate with other applications. In other cases we may choose to use messaging within an application. We'll consider EJB container services for JMS messaging, and how to decide when to use asynchronous messaging as an implementation strategy.

• Authentication and authorization issues
  And especially how they relate to web applications.

• Using XML in J2EE applications
  XML is a core J2EE technology, and XML is becoming increasingly important in web applications and in the enterprise. We'll look at how XML can be used effectively in J2EE applications, and areas in which the use of XML may prove counterproductive.

• Caching issues
  Most applications, and especially web applications, need to cache some data to minimize the expense of querying persistent data sources. We'll consider the potential benefits and challenges of implementing caching.

After we discuss each issue, we'll make the relevant decisions for our sample application. While the sample application is just one – relatively simple – J2EE application, this serves to highlight many common problems and demonstrate the trade-offs called for in real projects.

We won't talk about data access in this chapter. This important topic will be addressed in Chapters 7, 8, and 9. We'll also pay relatively little attention to the implementation of the web tier. This will be discussed in detail in Chapters 12 and 13.