Resource Adapters A standard architecture for connecting the Java2 Enterprise Edition (J2EE) platform to heterogeneous EIS's
What's a Resource Adapter   What's an EIS
The Resource Adapter plays a central role in the integration and connectivity between an EIS and an application server.

It serves as the point of contact between application components, application servers and enterprise information systems (EIS).

A resource adapter, along with the other components, must communicate with one another based on well-defined contracts that are specified by the J2EE Connector Architecture.
  An EIS (Enterprise Information System) can be thought of as an existing source of enterprise information, such as an ERP system like the Oracle E-Business Suite, SAP R/3, a mainframe transaction processing system, or an RDBMS.

EISs are usually not implemented in Java, so the J2EE Connector Architecture provides mechanisms to bring these systems into the J2EE application arena through the specification and use of Resource Adapters, Common Client Interfaces, and Quality of Service contracts.
What Comprises a Resource Adapter   How does a Resource Adpater work with an EIS
To enable seamless integration with an application server, a resource adapter must abide by guidelines, known as system-level contracts, that are defined by the Connector Architecture.

These contracts exist between the application server and the EIS, and are implemented through the Resource Adapter. They also specify how a system external to the J2EE platform can integrate with it by supporting basic functions that are handled by the J2EE container. There are three major categories of these functions:

  • Connection management
    The connection management contract allows applications to connect to an EIS. It also enables the application server to utilize pooling.

  • Transaction management
    The transaction management contact allows an application to manage and perform transactional access across one to many EIS resource managers.

  • Security
    The security contract provides support for secure access to the EIS.
Each of these contracts define what the resource adapter must support to achieve connectivity and interoperability between the EIS and any compliant application server.

  A Resource Adapter is specific to the EIS for which it was developed or purchased. It provides the system level operations needed to communicate and operate with the EIS. While a Resource Adapter is specific to the EIS it represents, it is not specific to a particular application server and can therefore be reused across any J2EE application server.

The Resource Adapter exposes its capabilities to the application server through a Common Client Interface. Using the exposed Common Client Interface, the application server can effectively incorporate the services of the Resource Adapter into its operations while insulating the applications themselves from the underlying implementation of the EIS.

Important requirements for effective and scalable integration with EISs are system services such as
  • connection management and pooling

  • transaction management to support transactions internal to the EIS and across multiple EIS systems

  • error logging and tracing

  • a security framework enabling both container managed and component managed sign-on.
Resource Adapter Implementation

The J2EE Connector Architecture specification defines interfaces, which implement the three contracts summarized above. Most of these interfaces are mandatory, in that they must be implemented by the adapter, while others do not need to be implemented. These non-mandatory interfaces are provided for the developers so they can maintain a consistent programming model if they choose.

Vendors can define and implement their own interfaces, with no effect, as long as methods, which are required by the architecture, are provided in an EIS-specific manner. In the end, these vendor-defined interfaces will be very similar to the provided interfaces. All of the interfaces deliver a useful and standard framework that an EIS vendor can follow to develop a resource adapter.

Note. JDBC 3.0 supports Resource Adapters.
All major database vendors have committed to supplying Resource Adapters


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