As open source technology is gaining more popularity in the press and among the general population, there still seems to be a lack of knowledge of what is available via open source amid many software development projects. While the mainstream media and the average computer user thinks of Linux whenever the term open source is brought up, this article looks at the amazing wealth of technology available to Java software development teams. For years there have been promises of code reuse resulting from the use of object-oriented programming. The open source community is delivering on that promise today.

If you're a Java developer, there is a gold mine of good open source technologies available now to assist you with your projects. There is an open source project covering nearly every category of technology, component, or framework that you can envisage.

The Communities and Projects
Apache Software Foundation
The Apache Software Foundation, best known for its Apache Web server, is probably the most well-known source for open source projects. Apache products are widely considered to be best-of-breed in their categories. Apache's Jakarta project is home to some of the best Java development technologies available. In the Java community, one of the most well-known open source projects is the Struts project, which is part of this Jakarta family. It can be arguably stated that Struts has become a de facto standard framework for implementing Java Web applications.

One of the few open source development projects in wider use is the Ant build system, which is another project from the Apache team. Ant is a robust, enterprise-ready tool for building and deploying your Java applications. Any Java project that is not using Ant as a part of its build process today should be doing so. Apache is also the home of the most widely used Java XML libraries, Xerces and Xalen. It's hard to find a Java project using XML that doesn't make use of these libraries.

Another popular open source project from the Apache group is the Tomcat server. Tomcat is the official reference implementation of the Java servlet and JSP specifications. Tomcat is a capable server and has widespread usage, particularly as a development test server. The most significant piece of J2EE not supported by Tomcat is the EJB specification. Many projects that don't use EJB technology will use Tomcat as a testing environment on local developer workstations, even if the production server will ultimately be a commercial J2EE product such as WebSphere or WebLogic. Tomcat is also used in many production environments.

JBoss, Inc.
If you want a full J2EE application server that does give you access to EJB technology, the open source community has a powerful offering that meets your needs as well. The JBoss server, created and supported by the JBoss group, is a standards-compliant J2EE application server. The JBoss group is proving that open source can also be adapted to a successful commercial business model with its recent announcement of 10 million dollars of venture funding led by the venture capital firm, Matrix Partners.

The Apache group has a competitor in the works as well. The Apache Geronimo project will be the J2EE application server from the Apache group. Many of the Geronimo developers are former JBoss developers. As of this writing, Geronimo had not yet released a J2EE-compatible server, but rather what they call "technology demonstrations." Geronimo is a great example of what will be an enterprise application built on top of many other open source projects. Rather than build from the ground up, the Geronimo team is wisely making use of many open source projects already in existence. This allows the Geronimo team to rapidly build an enterprise-class application server in a time frame that would be daunting to any commercial development team.

JUnit
One of the hottest trends in application development today is the concept of test-driven development. This philosophy places a new emphasis on creating unit tests for all of your methods as you write them. Here's another area where open source shines. The de facto standard unit-testing framework for Java development is JUnit. JUnit greatly simplifies the creation and execution of unit-level tests for your code. As I've stated about Ant, if your project is not using JUnit, it should be.

SourceForge
While Apache is probably the most well-known place for open source Java technology, the biggest resource for developers is the SourceForge community Web site. SourceForge is the home of thousands of open source projects. At the time of this writing, they had over 12,000 Java projects listed on their site. Not that these are all active and useful projects. Many of them are lying stagnant with outdated code, or no files have been produced. Because of this, when you do a search on the SourceForge site, don't get too excited about all the results until you've had the chance to actually browse the details of the projects to make sure they contain useful technology. For those developing open source projects, SourceForge provides free hosting services for your projects. SourceForge is usually the first place to check if you are looking for an open source component covering a particular technology.

The SourceForge site is divided into subcommunities called foundries. Each foundry is a community focused on a specific technology. Our primary interest here is in the Java foundry. The Java foundry is a central location where you can find news, announcements, discussions, and articles about the Java projects hosted by SourceForge.

Tigris.org
A lesser-known site that provides good open source projects is the Tigris.org site. Tigris.org is an open source community focused on building better tools for collaborative software development. While not nearly as large as the SourceForge community, a nice thing about the Tigris site is that all of its projects are active and ongoing. Thus, you won't come across any dead or barely started projects with no usable code as you often do on SourceForge. The Tigris projects don't have a complete Java focus, but rather tend to be focused on more of the noncoding-related tasks that are part of the software development cycle.

A particularly good project from Tigris is ArgoUML. ArgoUML is a full-featured UML modeling tool implemented in Java. For those who are not familiar with ArgoUML and are in need of a good software modeling tool, check out ArgoUML. I think you'll be impressed with what you can get for free. One of the most intriguing and perhaps most useful projects that Tigris offers is a library of reusable software engineering document templates in the ReadySET project. Here you'll find templates covering all your software project deliverable documents, including project planning, requirements, architecture and design, and deployment and test documents.

Java.net
New this year to the open source community space is Sun's Java.net community. This is really much more than an open source community. The open source projects are just a piece of the Java.net community. This community also provides articles, discussion forums, mailing lists, news, and blogs related to Java technology. This is a great educational site for those new to the Java platform and those who wish to expand their knowledge of the platform and technologies available. With all of its offerings, this is a well-rounded collaborative community site where projects, discussions, and other offerings are divided into communities of interest related to specific technologies under the Java umbrella. This is a nice distinction that this site offers. If you're looking for a project in a specific technology, say a Java networking project, you can search within that specific community. For an experienced Java developer, a periodic review of this site will help you keep current on emerging Java technologies.

Open Symphony
Open source J2EE enterprise class components can be found at the Open Symphony project. This is a project that emphasizes quality over quantity. You won't find nearly as many components and technologies available here as on some of the other open source communities, but those you do find are very robust, scalable, enterprise-ready components that have been used in many commercial applications. In their own words, their components stress simplicity, integration, plugability, and specification compliance. Popular components available here include a good workflow engine, OSWorkflow, and WebWork, an MVC framework alternative to Struts. The components here are all developed by the same core team, and thus they cover a spectrum of enterprise technologies. Unlike some of the larger community sites, you won't find 10 components here trying to accomplish the same thing. For the most part, these components are designed to complement each other and give the developer the building blocks necessary to develop an enterprise-scalable application. There is a very unrestrictive common license adopted for all of the Open Symphony projects as well, allowing for source and binary redistribution and/or modification in both commercial and open source projects.