August 15, 2001, 3:43 PM — Java can be used many ways in Web applications, from the simple, old-fashioned CGI to the complex J2EE (Java 2 Enterprise Edition) framework. With help from the open-source community, Lutris Technologies Inc. has developed Enhydra, a unique, pure-Java framework for enterprise Web applications.
Enhydra is a collection of open-source Java projects made commercial by the addition of Lutris' documentation, code samples, and support. These added benefits are worth the scant investment -- $995 per CPU, as compared to J2EE fees of as much as $25,000 per CPU -- if you buy into Enhydra's approach to Web applications. Lower-cost alternatives to J2EE can only do the market good, but at the same time, it is reasonable to question the long-term wisdom of adopting any enterprise Java framework but J2EE.
This latest Enhydra release updates Java compatibility to Java Developer's Kit Version 1.3, adds graphical application creation wizards, enhances the InstantDB Java database, extends support to wireless applications, and strengthens the Kelp development toolset.
To appreciate Enhydra 3.52's uniqueness, you should understand how Sun Microsystems Inc. constructs Web applications. In Sun's Java servlet model, a Web server passes HTTP requests from users to the Java servlet responsible for the requested information. The servlet parses the user's request, interacts with databases and back-end systems as needed, and produces the dynamic Web page that's displayed in the user's browser. An extension of servlets, JSP (Java Server Pages) uses HTML and XML templates to shape the application's output.
Servlets and JSP work very well, but they have been criticized for failing to steer developers toward creating tiered applications. In contrast, Enhydra forces a sharp delineation between an application's presentation and business tiers. Enhydra developers can work independently on business logic and presentation code (in this case, HTML), freeing each developer to focus on his or her strongest skills. Enhydra weaves the separate tiers together at run time.
The key to Enhydra is Lutris' XMLC (XML compiler). Instead of marking HTML and XML documents with special tags that let a presentation engine such as JSP know where to insert data, a developer working with XMLC creates an ordinary, static HTML or XML document that's displayable on any browser. XMLC digests the document and creates an object model that the Java developer uses to produce a dynamic presentation. Aside from being easier to use than JSP and facilitating the advantageous separation of development roles, XMLC extends its capabilities to all HTML/XML dialects, including wireless variants such as WML (Wireless Markup Language) and cHTML (compact HTML).
XMLC's downside is that major changes to the HTML or XML document require it to be recompiled. Conceivably, an Enhydra project could bounce between development teams several times before it's ready for delivery. JSP makes it easier for developers to quickly tweak the presentation layer because the code and HTML share a single file.
Enhydra 3.52 does not include an IDE (integrated development environment). Instead, it enhances existing IDEs, such as Borland Software Corp.'s JBuilder and Oracle Corp.'s JDeveloper, with graphical tools that ease application creation, database connections, and management.
Enhydra's new graphical application wizard generates the template files and directory hierarchy needed for new projects. Supplant the wizard's sample code with some real Java and HTML is simple. The wizard creates a make file you use to rebuild the application each time you change it. The wizard makes the process easier, but the frequent rebuilds mean Enhydra projects take longer than those that use integrated approaches.
Enhydra 3.52 Web applications can run on their own or under an Apache Software Foundation, iPlanet E-Commerce Solutions, or Microsoft Corp. Web server. A stand-alone Enhydra application runs under Enhydra Multiserver, a servlet/JSP host that has a built-in low-volume Web server. Multiserver hosts Enhydra's administrative console. Using the Web interface, you can start, stop, and add new Enhydra applications to a running host. Multiserver includes load balancing and fail-over capabilities.
Enhydra 3.52 delivers an impressive bundle of functionality at a low cost. We like XMLC's clean separation of application tiers, but that's tempered by the need for frequent rebuilds and the chance that HTML/XML documents will fall out of sync with the Java code that manages them. Moreover, some developers may not be keen on learning skills they can't use everywhere.
