Introduction

Integration complexity

As you develop Web-based applications, you probably find that you need to integrate those applications with the resources and data available in at least one enterprise information system (EIS), such as an enterprise resource planning (ERP) system, a supply chain management (SCM) system, or a transaction processing monitor (TPM). Such integration is the essence of e-business strategy: we leverage and transform existing infrastructure, combining it with Web and other open technologies to support new business processes, such as business-to-business (B2B) transactions.

Prior to the advent of the J2EE Connector Architecture, integrating a J2EE application and an EIS was complex and problematic, because no standard for such integration existed. Each EIS vendor supplied its own solution to the problem. An EIS vendor usually didn't support all J2EE application servers. All of this made it difficult to write truly portable applications that integrated with enterprise information systems; a custom effort was required to integrate each application server-EIS combination.

JCA simplifies integration

The J2EE Connector Architecture (JCA) resolves the problem of connecting a J2EE application server to an EIS. By complying with the JCA standard, an EIS vendor ensures that its EIS will integrate easily with any Java-based application server. Likewise, the application-server vendor needs only to ensure its product is enabled for JCA connectivity, rather than customizing its product for every EIS on the market. Any JCA-enabled application server can integrate with any JCA-compliant EIS.

Introduction to the J2EE Connector Architecture

Elements of JCA

JCA is composed of three primary elements:

• System contracts
• Client API
• Resource adapter module

Each of these elements plays a specific role in JCA. We'll take a high-level look at each element separately, then move on to the more complex discussion in the next section.

System contracts

System contracts define the connection between the application server and the EIS. The EIS side of the system contract is implemented by a resource adapter -- a system-level software driver specific to the EIS. The application server and the resource adapter collaborate by means of the system contract to provide secure, robust, scalable access to the EIS.

Three types of system contracts are defined:

• The connection management contract enables physical connections to the EIS and provides a mechanism for the application server to pool those connections.
• The transaction management contract supports access to an EIS in a transactional context. Transactions can be managed by the application server, providing transactions that incorporate other resources besides the EIS, or they can be internal to the EIS resource manager, in which case no transaction manager is required.
• The security contract supports secure access to the EIS.

How system contracts are implemented on each side (application server and resource adapter) is not specified by JCA; they can be implemented as each vendor sees fit.

Client API

The second element of JCA is the client API. The API can be specific to the resource adapter or it can be the standard Common Client Interface (CCI) as defined by JCA. The CCI is meant to be used by vendors to provide integration tools and frameworks, making it easier for developers to access enterprise systems. It is recommended (but not mandated) that the resource adapter make use of the CCI.

Resource adapter module

The resource adapter module contains all of the elements necessary to provide EIS connectivity to applications. Specifically, the resource adapter module includes the following components:

• The Java classes and interfaces that implement the resource adapter
• Any utility Java classes required by the resource adapter
• Any EIS-specific platform-dependent native libraries
• The deployment descriptor

Application servers make use of the deployment descriptor supplied with a resource adapter to configure it to a specific operational environment.

Resource adapter module packaging

Introduction to the J2EE Connector Architecture

All of the resource adapter module's files are packaged into a resource adapter archive (RAR) file using the Java archive (JAR) file format. All Java classes and interfaces are packaged in a JAR file, which is then contained by the RAR file. The native files are packaged in the RAR file, also. The deployment descriptor is named ra.xml, and is located in the META-INF folder of the RAR file.

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