Java Reference
In-Depth Information
Java EE works within the realm of the Middle tier, although it touches both the Client and the EIS
tiers. The Middle tier receives requests from the Client tier application. The Middle tier's Web layer
processes the request and prepares a response, which it sends back to the Client tier, whereas the
Business layer applies the business logic before persisting it in the EIS tier. Within the Middle tier,
there is l uid communication between the layers and the EIS tier, while preparing the response to the
Client tier. A multitier architecture can be represented visually, as in Figure 2-1.
Client
App
Browser
Client Tier
Client Machine
Web Container
Web Layer
JSP/JSP
Servlet
EL/JSTL
Web Sockets
Middle Tier
EJB Container
Business
Layer
EJB
Java EE Server
EIS Tier
Database
Database
Database Server
FIGURE 2-1:
Multitier architecture showing the interaction between tiers
THE CLIENT TIER
The Client tier is usually a browser that connects to the Java EE server via Hypertext Transfer
Protocol (HTTP), although it can be any application on any machine as long as it behaves as a client
in a server‐client relationship. The client application sends a request to the server for a resource;
the server then processes the request and returns a response. This is usually the extent of the
relationship between the client and the server.
NOTE
The Client tier is often referred to as the Presentation tier.
