Client Tier

This section considers constraints on the client based on the platform and programming language.

• Platform
• Browser application
• Stand-alone Java application
• Other
• Platform independence : Recently, browsers act much like platforms. In such cases, the application will still have to deal with differences in browser "platforms."
• Language / Technology
• Complexity / Facility of programming : Control a technology as java is easier than to adapt constantly to new emergent technologies.
• Availability of expertise
• Desire to integrate with other legacy application clients
• Extensibility : Use a full oriented Object environment facilitate extensibility.
• Modularity : Use a full oriented Object permit to make independent module that are easily shareable.
• Maintenance : The latest technologies evolve quickly and quickly become obsolete.
• Test : Check a Java application is more easier than test Web application.
• Debugger : In web application, debugger can't use, or use with little options.
• Unit test / modularity : A framework full object is easily realizable and can offer object with no bug.

Java client side with Applet :

• Advantages
• Ability to download code over the network
• Run it on a variety of desktops
• Offering a rich user interaction
• Secure
• Disadvantages
• Browser incompatibility
• Slow download time
• Sandbox environment to much restricted (Security)
• Balance : The applet offered an attractive solution but with major disadvantages. So, Java morphed from an applet-based language into the programming platform of choice on the server.

Java server side with Servlet / JSP :

Focus shifted heavily from the client to the server side, using server-based technologies, it was easier from a program maintenance viewpoint to control from the server the user interface for the client. The user interface centers around markup technologies like HTML, XML, XHTML, and so on.

• Advantages
• Browser independent - can generate simple HTML document
• Support for multiple kinds of clients, especially thin clients (Web, PDA, Phone, ...)
• Disadvantages
• HTML / XML Limitations (interactivity limited)
• Must use DHTML for rich interaction (browser dependant) or Applet, other plug-in.
  DHTML is difficult to write and maintain and has notorious browser deployment problems.
• Balance: This approach doesn't fit for rich interactive application. A browser-based email client serves as a good example. Although browser-based email clients are quite popular, traditional email clients are more prevalent, especially in the workplace, where there is a need to sift through lots of email, apply filters, and be able to work offline in certain scenarios.

Java comes back on the client (Java plug-in / JavaWebStart) :

Some of the ease-of-use and ease-of-programming features associated with Java Web Start include many advantages.

• Advantages
• Portability : Java Web Start is available on Windows, Solaris, and Linux, and is expected to be ported to other platforms.
• Caching: Applications launched with Java Web Start are cached locally. Thus, an already-downloaded application is launched on par with a traditionally installed application.
• Maintainability: If the remote application is updated, Java Web Start updates the locally cached version at the application's next invocation or immediately (depends on the configuration we want).
• Easy launching: Java Web Start allows applications to be launched independently of a Web browser. The application can also be launched through desktop shortcuts, making launching the Web-deployed application similar to launching a native application. A web page can also launch application, it is the sane link that download and install the application the first time.
• Ability to work offline: An application can be used in situations where launching through the browser is inconvenient or impossible. If all resources can be find locally, the application can work offline.
• Disadvantages
• Install Java Web Start with JRE (but automatic)
• Time to download Client the first time and for new versions (but automatic)
• Balance : The best of the 2 worlds : client/server - web application.

Plusieurs acteurs s'affrontent sur ce domaine et pas des moindres :

• Sun / Java: avec Java Web Start ( http://java.sun.com/products/javawebstart/ )
• Microsoft / .Net: No-Touch Deployment
• Macromedia / Flash: ( http://macromedia.com )
• XUL: soutenu par la communauté libre et la fondation Mozilla ( http://www.XULfr.org )

Voir les exemples disponibles:

• Macromedia / Flash
• Rich Internet Applications: ( http://macromedia.com/resources/business/rich_internet_apps/ )
• Démos de la société Laszlo(fr): ( http://www.laszlosystems.com/demos/ )