When Sun released J2EE to capture the growing e-business market, itchanged Java from a language to an enterprise platform.
Several key players such as BEA and Oracle have pledged theirsupport and endorse J2EE standards in their application serverproducts. Several other companies are either already using the Javaapplication server or are thinking of using it in the near future.These companies are scrambling to come up with a scalable enterprisearchitecture that works with existing technology and also grows withfuture changes. However, developing scalable and adaptableenterprise architecture is a difficult and time-consuming task.Several software-engineering principles such as OO methodology andsoftware patterns need to be used when constructing the enterprisearchitecture so it will last.
To solve this Cybelink created Jlink, a vendor-neutralframework based on Sun's J2EE Blueprint recommendations andguidelines. Architected at a high-level, Jlink can be easily adaptedto work with any vendor-specific, Java-based application server suchas WebLogic and WebSphere. In this three-part series we'll discussthe Jlink framework; in Part 1 we'll discuss the Servlet/JSP portionof Jlink and describe the problems associated with the Servlet/JSPtechnology. In Part 2 we'll describe the Jlink architecture and howit solves the Servlet/JSP problems. In Part 3 we'll describe theworkings of Jlink and provide an example.
Web Programming Modeland Servlet/JSP Container
Before going into the details of Jlink, we'll discuss the Webprogramming model and explore how the Servlet/JSP container supportsit. Any Servlet/JSP-based Web application can be modeled using thefollowing simple actions: a user submits a request using a Webbrowser and clicking a button or a URL link. The HTTP request firstgoes to the Web server and if it's plain HTML, it sends the HTML pageto the browser. If the request needs to execute a Servlet/JSP, theWeb server passes the request to the Servlet/JSP container, whichprocesses the request by invoking the appropriate Servlet/JSP andsending a response back to the browser. The Servlet/JSP might processthe request itself or send it to a JavaBean or EJB, extract theresult, and transfer it to the browser via the Web server.
J2EE defines a Web container as a place where servlets andJSPs live, and it acts as a bridge between the client and EJBcontainers. The communication between the Web and EJB containers iscarried out by JavaBean components. A crucial aspect of Webdevelopment is to architect the middle tier, which processes the HTTPrequest and sends the results back to the browser. Jlink provides aneasy mechanism to handle HTTP requests from the browser and send themto the appropriate JavaBean component, which processes the resultsand sends them back to the browser. An HTTP request can be processedin one of the following ways:
- Within Servlet/JSP components
- Within JavaBean components
- Accessing the EJB business components using local calls orthrough RMI/IIOP
