Use Case For the Basic Example

The purpose of an Enterprise Service Bus (ESB), also known as a Java Business Integration (JBI) bus, is to provide a mechanism for different applications to exchange messages in a protocol neutral manner and provide services for processing those messages such as message transformation and dynamic routing. ServiceMix is an implemenation of JSR 208, the JBI specification.

The Basic example demonstrates how external ¹ applications communicate via the ESB. The techniques could be used to plug any external application into ServiceMix (e.g. SAP, Peoplesoft, spreadsheets, POJOs and EJBs) and allow it to communicate with other external applications or components within ServiceMix itself.

A common business scenario, which extends the Basic Example is that of a large department store distributor. This distributor sells products from many wholesalers to many retail outlets (i.e. department stores). The distributor presents a common interface for product ordering to each of its department store customers, however each wholesaler presents a different ordering interface to the distributor for the product the wholesaler supplies.

Using an ESB, the distributor has developed a number of components to receive department store orders and dynamically route and transform these orders to the appropriate wholesaler. The order flow is described as follows:

1. Using a web-based form, a user asks for data from a legacy application.
2. An HTTP request is formulated and sent to the HTTP binding component (BC). ²
3. The HTTP binding component transforms the HTTP message into a neutral form. This is called a normalized message.
4. The normalized message is routed through the Normalized Message Router (NMR) to a Service Engine (SE) ³ or BC that knows how to communicate to the legacy application.
5. The SE/BC transforms the message into a form that the legacy application understands.
6. The SE/BC passes the message to the resource adapter ⁴ for the legacy application.
7. The resource adapter communicates with the legacy application and obtains the requested data.
8. The requested data is transferred back to the web-based form, reversing the route.

The following diagram illustrates this:

In comparison, the Basic example, looks like the following diagram. This is a simplified diagram of the basic example. For a complete diagram, please see: Basic Example.

Please note: The Basic example uses inbound messages via the resource adapter, and most legacy applications won't support inbound messaging via the resource adapter.

1. External means the application is outside of the enterprise service bus.
2. Binding Component (BC): a BC provides connectivity to applications that are external to the ESB.
3. Service Engine (SE): a service engine provides business logic and transformation services to other components within the enterprise service bus.
4. Resource Adapter: a resource adapter provides connectivity between a specific external application and the ESB.