This section explains some of the basic concepts and terminology associated with developing component-based Jaguar applications in a three-tier environment. It is intended primarily to provide you with enough information to complete the tutorials and begin using EAServer Manager. For detailed information on Jaguar application development, see the EAServer Programmer’s Guide. For details on the EAServer architecture, see the EAServer Feature Guide.
EAServer implements a three-tier or multitier distributed computing architecture. In this model, three distinct elements work together to give users access to data:
A user interface, which can be a standalone client program or a Web application run in the user’s Web browser. Web applications can use JSPs, Java servlets, or Java applets to manage presentation and interaction with the end user. Clients use stubs to communicate with application components running in the middle tier.
Middle-tier components, which access data from one or more databases, apply business logic, and return results to the client for display.
The back-end database, which hosts application data.
An EAServer application consists of one or more packages and a client user interface to interact with end users. Packages consist of components, and components are made up of one or more methods.
In EAServer, a component is simply an application object that consists of one or more methods. EAServer can host, manage, and execute components such as Enterprise JavaBeans, CORBA-compliant Java and C++ components, and ActiveX nonvisual components. Components typically execute business logic, access data sources, and return results to the client.
A package is a collection of components that work together to provide a service or some aspect of your application’s business logic. A package defines a boundary of trust within which components can easily communicate. Each package acts as a unit of distribution, simplifying deployment and management of related components.
A stub is a Java or C++ class generated by EAServer Manager. The stub acts as a proxy object for a Jaguar component. A stub is compiled and linked with your Java applets or client application. A stub communicates with Jaguar to instantiate and invoke a method on a component in the middle tier. Stubs make a remote Jaguar component appear local to the client.
A skeleton is a Java or C++ class generated by EAServer Manager. The skeleton acts as the interface between the EAServer runtime and the user code that implements the component.
A Web application allows you to deploy Java servlets, JavaServer Pages (JSPs), and related Web files as a unit. Servlets and JSPs in a Web application can invoke EAServer components, allowing you to develop user interfaces that run over the Web without using Java applets.
A server is an operating system process that provides the runtime environment to execute components and Web applications in response to client requests. The tutorials use the preconfigured server named Jaguar, though you can define and configure your own servers in EAServer Manager.
EAServer supports several network communication protocols. These protocols are of interest for the tutorials:
IIOP is a standard CORBA protocol for component invocations. Standalone client applications and client applets use IIOP to invoke components. You do not need to know IIOP; the generated stubs take care of all network communication.
HTTP is the standard Web protocol for file downloads and form requests. Web browser clients use HTTP to invoke servlets, JSPs, and to download Web pages.
Each
supported protocol requires a listener to be
associated with the server in EAServer Manager. A listener defines
the port number, host name, and protocol for client connections
to the server. You do not need to configure any listeners to run
the tutorials, unless you plan to run client applications on a different
machine than the server. In that case, you must change the listener
host names from the default, localhost,
to the server machine name.
For information on listeners and other supported protocols, see “Configuring listeners” in the EAServer System Administration Guide. For a tutorial that uses the secure versions of IIOP and HTTP, see the EAServer Security Administration and Programming Guide.
