Some external enterprise systems that need to be integrated from an application don't offer standard interfaces or Java APIs. Legacy systems as well as other systems being used within the organization may fall under this category. The Java EE Connector Architecture (JCA) API can integrate these so-called Enterprise Information Systems (EIS) into Java EE applications. Examples of EISs include transaction processing systems, messaging systems, or proprietary databases.

JCA resource adapters are deployable EE components that integrate information systems into the application. They include contracts such as connections, transactions, security, or life cycle management. The information system can be integrated better into the application compared to other connection technologies. Resource adapters are packaged as Resource Adapter Archives (RAR) and can be accessed within the application using the functionality of the javax.resource package and its sub-packages. Some EIS vendors provide resource adapters for their systems. For developing and deploying resource adapters, refer to the JCA specification.

JCA offers a variety of integration possibilities for external information systems. However, the standard is not widely used and has not a high acceptance by enterprise engineers. Developing resource adapters is quite cumbersome, the JCA API is not well known among developers, and companies usually choose to integrate systems in other ways. In fact, it should be considered whether the effort of writing resource adapters is preferred over integrating information systems using other integration technology. Other solutions include integration frameworks such as Apache Camel or Mule ESB.