Adobe Flex and AIR have strong ties to Java in their history, including an Eclipse based IDE, and full feature data services products built in Java to run in Servlet containers. However, even with the strong ties to the Java Platform, Adobe AIR has no native way to use Java on the client. In addition, AIR applications have fairly limited access to local resources when compared with other desktop platforms.
Generally speaking, Adobe has avoided adding native operating system features and local access for philosophical reasons – not technical. Adobe’s main apprehension is that such additions would make portability across operating systems more cumbersome. Although Adobe’s concerns are reasonable for a platform vendor, the community has responded by offering its own solution in the Merapi Project.
The Merapi’s Project website describes the bridge this way:
Merapi is a Java™ application, intended to run on a user's (client) computer. Merapi connects other Java™ applications on the user's computer to Adobe AIR™ applications that the user has installed.
It isn't magic. You have to develop your Adobe AIR™ application in a way that allows it to connect to Merapi. Merapi acts as a "middle man", passing objects between your AIR™ application and your Java™ application.
Using Merapi, Adobe AIR™ applications can "talk" to other software that the user has installed on their computer. In addition, Merapi allows AIR™ applications to serve as a user interface to just about anything that a Java™ application can do on a user's computer.
Another great summary of the project:
Using Merapi, Adobe AIR™ applications can "talk" to other software that the user has installed on their computer. In addition, Merapi allows AIR™ applications to serve as a user interface to just about anything that a Java™ application can do on a user's computer.
Merapi is another great example of the community filling the gap where vendors are unable to offer features desired by developers. To learn more about Merapi, check out this Step-by-Step guide and the following overview. In addition, here is a blog post from one of the contributors, Adam Flater, in early 2008 introducing the project.