Portability Versus Interoperability

EJB 2.0 Interoperability Goals

Because J2EE applications are typically multitier, Web-enabled applications, they generally consist of one or more components that are hosted inside a container. The J2EE and EJB specifications describe four types of containers:

• EJB containers that host enterprise beans

• Web containers that host JSP pages, servlets, and the more common HTML pages and images

• Standalone Java client applications

• Applet containers

Note

Currently, there is no requirement that applets should be capable of invoking remote methods on an enterprise bean. Although certain vendors might support this in their products, it's not a requirement yet.

Figure 20.1 shows a generic heterogeneous environment configuration in which containers from various vendors need to interoperate .

Figure 20.1. Containers from different vendors can take advantage of interoperability.

There are four primary goals for the new interoperability requirements in the EJB 2.0 Specification:

• To allow components deployed in one J2EE container to access services from an enterprise bean that is deployed in a different J2EE container. The containers can be from different vendors and on different operating system platforms.

• To not put any new programming requirements on the application developer compared to the previous EJB Specification.

• To help ensure that J2EE products from different vendors will be compatible out of the box, regardless of such things as the operating system or vendor.

• To take advantage of the standards work that has already been done by such organizations as Object Management Group (OMG), World Wide Web Consortium (W3C), and Internet Engineering Task Force (IETF). This allows customers to leverage industry standards and protocols when accessing services from the containers and provides for a bigger acceptance market.