Java Reference
In-Depth Information
specification, and they are deployed to production, where they are run and managed by
the Java EE server.
Java EE Clients
A Java EE client is usually either a web client or an application client.
Web Clients
A
web client
consists of two parts:
• Dynamic web pages containing various types of markup language (HTML, XML,
and so on), which are generated by web components running in the web tier
• A web browser, which renders the pages received from the server
A web client is sometimes called a
thin client
. Thin clients usually do not query databases,
execute complex business rules, or connect to legacy applications. When you use a thin
client, such heavyweight operations are off-loaded to enterprise beans executing on the
Java EE server, where they can leverage the security, speed, services, and reliability of
Java EE server-side technologies.
Application Clients
An
application client
runs on a client machine and provides a way for users to handle
tasks that require a richer user interface than can be provided by a markup language. An
application client typically has a graphical user interface (GUI) created from the Swing or
the Abstract Window Toolkit (AWT) API, but a command-line interface is certainly pos-
sible.
Application clients directly access enterprise beans running in the business tier. However,
if application requirements warrant it, an application client can open an HTTP connection
to establish communication with a servlet running in the web tier. Application clients writ-
ten in languages other than Java can interact with Java EE servers, enabling the Java EE
platform to interoperate with legacy systems, clients, and non-Java languages.
Applets
A web page received from the web tier can include an embedded applet. Written in the
Java programming language, an
applet
is a small client application that executes in the
Java virtual machine installed in the web browser. However, client systems will likely
need the Java Plug-in and possibly a security policy file for the applet to successfully ex-
ecute in the web browser.
Web components are the preferred API for creating a web client program, because no
plug-ins or security policy files are needed on the client systems. Also, web components
