Transactional support is fundamental to application development. While most data sources are transactional in nature, some data sources like the file system are not.
In typical J2EE deployments, applications often need to interface with other applications through file-based messages. Such deployments would benefit from an adapter that would buffer all file operations and provide a transactional view to the file system.
This article, targeted at developers, demonstrates how J2EE Connector Architecture and JTA specifications can be implemented to build such an adapter, XAFileConnector. We'll also suggest enhancements to extend the adapter functionality in light of the new proposed draft connector specifications.
Most applications are bound to the local file system. They use the file system to store and share data. Often the success of interactions with the file system needs to be tied to the successful completion of other actions involving other Enterprise Information Systems (EIS). For instance, we often encounter situations where a record is to be deleted from the database only after it has been successfully written to a file. While the same can be easily built into the application logic, it would be infinitely more neater if we could develop an extension on the file system that would help us include the file operations such as "create", "read", "update", and "delete" as part of a transactional unit of work that could be committed or rolled back as a group. This extension is called a Resource Adapter. The ubiquitous presence of the file system and the role it plays in Enterprise Application Integration strategy justify the need to build such a resource adapter.
For a J2EE-managed environment, i.e., an environment characterized by the presence of a container for runtime support, J2EE recommends Connector Architecture as a standard way of integrating heterogeneous EISs with the application server. The Connector Architecture specifies application- and system-level contracts to be implemented by the EIS. The resource adapter implements the EIS side of the contracts. The adapter uses a native interface specific to the underlying EIS, runs in the containers address space, and manages access to the EIS resources. Adherence to the Connector contracts on one hand ensures that the same adapter can be deployed on different vendors' containers, while ensuring that application and tool developers have a standard interface to program to for accessing different EIS systems. Among the set of contracts that need to be implemented by the resource adapter to seamlessly plug-in to any J2EE platform is the XAResource transaction contract. This contract defines the communication interfaces between the parties involved in a distributed transaction. Implementation of this interface by the adapter enables seamless propagation of transaction context and allows the associated resource manager (RM) to participate in a two-phase commit protocol along with other resources.
