J2EE and XML Development

Geared toward experienced developers, this reference demonstrates how Java 2 Platform, Enterprise Edition (J2EE), and XML technologies can be used together to create more robust distributed applications and software systems. The use of XML technology to extend and enhance the capabilities of the J2EE platform is covered in detail.

Discussed are J2EE and XML integration at each layer of an n-tier distributed application model. Design patterns, tradeoffs, and decision criteria are provided in terms of individual XML and J2EE technology combinations.

Hot topics in application integration are also covered, including Web services, architectures, and business partner integration.

User interface development

This chapter

Demonstrates use of XSLT with Java servlets
Compares pure J2EE user interface development with an XML approach
Shows how to build multidevice and multilocale
Covers XML web publishing frameworks

Creating a robust presentation layer for your J2EE application is a challenging endeavor. This is so because the vast majority of J2EE applications are web-based, also known as "thin-client", applications. In this chapter, we examine some emerging challenges in J2EE user interface design and discuss ways you might use XML technology to overcome them.

The remainder of the chapter focuses on overcoming the limitations of the pure J2EE approach using XSLT technology. First we develop an XSLT-based presentation layer from scratch. Then we use XSLT from within a web pub-lishing framework to discover the benefits and drawbacks of using a third party API.

The goal of this chapter is not to convince you that one architecture or product is superior to another. We wish only to make you aware of the avail-able options, see them in action, and understand the positive and negative aspects of taking each approach.

5.1 Creating a thin-client user interface

In this chapter, we focus almost exclusively on web-based, thin-client distrib-uted applications. Before diving into the details of overcoming challenges associated with these types of applications, we should take a moment to dis-cuss what they are and why building interfaces for them is so difficult.

DEFINITION A thin-client application is one in which the server side is responsi-ble for generating the user interface views into the application. The client side usually consists only of generic rendering software, e. g., a web browser.

If you have built web-based applications before, you are no doubt familiar with the thin-client architecture. Until recently, the burden of generating the user interface for your application on the server side was not too difficult. Two relatively recent developments, however, are now making the development and maintenance of your presentation layer components more challenging.

5.1.1 Serving different types of devices

The first new challenge relates to the ongoing proliferation of web-enabled devices. It seems as though anything that runs on electricity these days now has a web browser on it. These "smart" devices include cell phones, PDAs, and refrigerators. (That only sounds like a joke.) The trouble with these smart devices is that they are usually quite dumb, virtually light years behind the cur-rent version of your favorite computer-based Internet browser. Some under-stand a subset of the HTML specification, and others require an entirely separate markup language. An example of the latter is the WAP-enabled cell phone, which requires web pages to be rendered using the Wireless Markup Language (WML).

DEFINITION WML is an XML-based presentation markup language specifically designed for web browsing on cellular telephones. These phones typically feature small display areas and very limited rendering capa-bilities. WML arranges content into a deck of cards (pages), each of which should contain very little data and uncomplicated navigation.

Creating a single, integrated user interface that can render content for various types of devices is difficult to do using the traditional J2EE (or ASP, or Cold Fusion, etc.) approach. User interface components in these technologies were not designed to change the entire structure of the generated content based on the type client requesting it. This means that, in order to serve web browser and cell phone client types from your J2EE web application, you must develop and maintain two separate presentation layers. One layer would generate an HTML interface, and the other a WML interface. Some updates to the applica-tion would require updates to both user interfaces. If you think managing two interfaces is scary, consider supporting three more types of client devices in the same application.

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