Legacy Integration

The ability for an enterprise application to connect to a legacy system such as Enterprise Resource Planning (ERP) or other type of Enterprise Information System (EIS) is essential to nearly any business. Connectivity to ERP systems such as SAP, Siebel, and PeopleSoft support nonrelational databases such as Adabas, Teradata, and IMS, and finally access to 3GL or 4GL applications cannot be achieved with ADO.NET or JDBC APIs. Legacy integration entails support for transactional technologies such as BEA Tuxedo, IBM CICS, DB/MVS, IMS/TM, ebXML, and EDI protocols. Modern integration with mainframe and legacy systems evolves around Web services, which simplifies interoperability between Java or .NET integration with legacy systems. This section discusses common techniques available to Java and .NET developers to connect to legacy systems.

In Java, the Java Connector Architecture is a standard mechanism to access legacy systems. A JCA implementation is offered in the form of resource adapters, which can be deployed in two ways. If an adapter is deployed under an application server, it is deployed under a managed environment. If a resource adapter is tightly integrated with the client application, it is deployed under a non-managed environment.

To establish a connection to a legacy application using JCA, a client invokes a getConnection() method on the ConnectionFactory class, which is part of the javax.resource.cci.Connection APIs.

 Connection con = (javax.resource.cci.Connection) connectionManager.allocateConnection( managedFactory, info ); 

The first argument corresponds to the connection factory; the second parameter includes authentication and any other information that has to be passed along.

A connection pool is utilized for adapters deployed under an application server. JCA also defines support for distributed transactions where a transaction is defined as a group of operations spanned across multiple legacy systems. For this transaction to succeed, all of the operations have to pass. If any of the operations fail, the entire transaction fails. Similar to the JDBC standard interface, the JCA 1.5 specification defines a Common Client Interface (CCI) to allow consistent access to disparate back-end applications. With the Adapter strategy discussed in this chapter, CCI APIs would be used within the Data Access Layer to access legacy systems. In addition, the JCA specification defines lifecycle management, work management, message inflow, and transaction inflow. JCA resource adapters that integrate with messaging software enable asynchronous communication between Java EE applications and legacy systems. See [JCA] for an introduction to Java Connector Architecture.

Java EE application servers offer out of the box JCA implementation. Commercial vendors such as iWay Software and SeeBeyond (acquired by Sun Microsystems) ship JCA-compliant resource adapters. These commercial solutions also enable .NET application connectivity to EIS systems using common Microsoft technologies such as ODBC, OLE DB, and ADO.NET. On the .NET side, integration with an internal to the enterprise legacy system such as IBM mainframe, messaging, and data sources, can be achieved via Microsoft Host Integration Server, see [HIS].

A discussion around integration with ERP and other EIS systems often ties to the overall workflow management, where connectivity between individual Java EE, .NET, and legacy systems is executed as part of the business workflow. Therefore, vendors such as SeeBeyond offer workflow management to orchestrate a business conversation among heterogeneous applications. This orchestration simplifies Service Oriented Architecture where individual services are connected in a consistent way. Microsoft BizTalk server provides similar functionality. Please refer to [SeeBeyond], [iWay], [MS_WSLegacy], and [JCA_Legacy] resources for more details.

In essence, there are two ways to approach legacy integration. For a basic Java or .NET legacy integration, commercial solutions and adapters can be used to integrate with back-end systems. On a larger scale, for Java and .NET applications participating in a B2B transaction or internal business workflow, commercial integration servers that supply workflow management can be leveraged. This is shown in Figure 6-5:

Figure 6-5. Legacy integration