Datasheet

Part I ✦ Introduction

Figure 1-2: J2EE Architecture (source: Javasoft)

Application components

Four application components are defined within the J2EE platform. They are as

follows:

✦ Application clients (Standalone Java clients)

✦ Applets (Java code which executes within a browser)

✦ Web components (JSPs, Servlets)

✦ Server components (EJBs, J2EE API implementations)

A product does not need to support all types of components; the norm is to provide

an implementation to support a particular component type. However, all compo-

nents are similar in that they run within a container. The container is responsible

for providing the runtime environment, the mechanism for identifying and under-

standing the file formats used for deployment, and the standard services for appli-

cation components to use.

The four application components are discussed in the following sections.

Application clients

Clients are generally stand-alone applications written in Java. They run within a vir-

tual machine and can use the J2EE standard services to access components located

within another tier. The J2EE standard services are usually provided on the client

via an installation of J2SE, or along with the distribution of the application itself.

Traditional development

SolarisHP-UXWin32

C Code

Java development

SolarisHP-UXWin32

Java

ByteCode

Direct compilation

Runtime VM Interpretation

Direct compilation

Intermediate compilationIntermediate compilation

Runtime VM interpretation

Java

Code

c539663 ch01.qxd 7/25/03 9:13 AM Page 6