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 (http://www.enhydra.org), 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.

Lutris delivers a muddled message with Enhydra. The vendor's Web site
refers to it as an open-source project, yet Lutris insisted to us that
Enhydra is not open-source. As it turns out, there are open-source and
commercial versions of Enhydra, but they're not the same. It's a
massive jumble that Lutris needs to clarify if it wants the place it
deserves in the competitive application server market.

» posted by ITworld staff

ITworld

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