client tier in j2ee

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Simplified Guide to the Java Enterprise Edition

The Client Tier 1-4 HTML Page Based Clients 1-5 HTTP Content Based Clients 1-5 Intranet Clients 1-6 Other Client Types 1-6 The Enterprise Information Systems 1-7 J2EE Declarations 1-7 J2EE Platform 1-8 J2EE Application Assembly and Deployment 1-8 Java Technology Standards for the J2EE Platform 1-9

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The Client Tier

Every application has requirements and expectations that its clients must meet con-strained by the environment in which the client needs to operate Your users and their usage patterns largely determine what type of client or interface you need to provide For example desktop Web browser clients are 51 THE CLIENT TIER popular for e-mail and e-sho

What are the J2EE client types?
This Client-Server model provides suitable architecture for distributed applications.
Types of J2EE Clients: There are various types of J2EE clients – Applet client, Application client, Servlet client, and JSP client, each with its own advantages.
What is client tier?
The client tier consists of the client programs and consoles that are used for development, administration, and other tasks and the computers where they are installed.
A tier is an abstract concept that defines a group of technologies that provide one or more services to its clients.
In multi-tier architecture, each tier contains services that include software objects, DBMS, or connectivity to legacy systems._{4 juil. 2023}

What are the tiers of J2EE?

The official J2EE application model, as discussed above, divides an application into a Client Presentation tier, a Server Side Presentation tier, and a Server Side Business Logic tier.
Enterprise information systems, such as databases, constitute a fourth tier.

The client tier consists of application clients that access a Java EE server and that are usually located on a different machine from the server. The clients make requests to the server. The server processes the requests and returns a response back to the client.

3.1 Client Considerations

Every application has requirements and expectations that its clients must meet, con-strained by the environment in which the client needs to operate. Your users and their usage patterns largely determine what type of client or interface you need to provide. For example, desktop Web browser clients are 51 THE CLIENT TIER popular for e-mail and e-sho

3.1.1 Network Considerations

J2EE clients may connect to the enterprise over a wide array of networks. The quality of service on these networks can vary tremendously, from excellent on a company intranet, to modest over a dialup Internet connection, to poor on a wireless network. The connectivity can also vary; intranet clients are always connected, while mobile clients experi

3.1.2 Security Considerations

Different networks have different security requirements, which constrain how clients connect to an enterprise. For example, when clients connect over the Internet, they usually communicate with servers through a firewall. The presence of a firewall that is not under your control limits the choices of protocols the client can use. Most firewalls are

3.1.3 Platform Considerations

Every client platform’s capabilities influence an application’s design. For example, a browser client cannot generate graphs depicting financial projections; it would need a server to render the graphs as images, which it could download from the server. A programmable client, on the other hand, could download financial data from a server and render

3.2 General Design Issues and Guidelines

While the J2EE platform encourages thin-client architectures, J2EE clients are not dumb. A J2EE client may handle many responsibilities, including: Presenting the user interface—Although a client presents the views to a user, the logic for the views may be programmed on the client or downloaded from server. Validating user inputs—Although the EIS a

3.3 Design Issues and Guidelines for Browser Clients

Browsers are the thinnest of clients; they display data to their users and rely on servers for application functionality. From a deployment perspective, browser clients are attractive for a couple of reasons. First, they require minimal updating. When an application changes, DESIGN ISSUES AND GUIDELINES FOR BROWSER CLIENTS 55 server-side co

3.3.1 Presenting the User Interface

Browser clients download documents from a server. These documents contain data as well as instructions for presenting that data. The documents are usually dynami-cally generated by JSP pages (and less often by Java servlets) and written in a pre-sentational markup language such as Hypertext Markup Language (HTML). A presentational markup language a

3.3.2 Validating User Inputs

Consider an HTML form for completing an order, which includes fields for credit card information. A browser cannot single-handedly validate this information, but it can certainly apply some simple heuristics to determine whether the information is invalid. For example, it can check that the cardholder name is not null, or that the credit card numbe

Code Example 3.2

JavaScript Validation Function Using DOM Hooks Validating user inputs with a browser does not necessarily improve the responsiveness of the interface. Although the validation code allows the client to instantly report any errors it detects, the client consumes more bandwidth because it must download the code in addition to an HTML form. For a non-t

3.3.3 Communicating with the Server

Browser clients connect to a J2EE application over the Web, and hence they use HTTP as the transport protocol. When using browser interfaces, users generally interact with an application by clicking hyperlinked text or images, and completing and submitting forms. Browser clients translate these gestures into HTTP requests for a Web server, since th

3.3.4 Managing Conversational State

Because HTTP is a request-response protocol, individual requests are treated independently. Consequently, Web-based enterprise applications need a mecha-nism for identifying a particular client and the state of any conversation it is having with that client. The HTTP State Management Mechanism specification introduces the notion of a session and se

3.4.1 Presenting the User Interface

Although a Java client contains an application’s user interface, the presentation logic behind this interface may come from a server, as it would for a browser, or it may be programmed from the ground up on the client. In this section, we discuss the latter case. THE CLIENT TIER Java applet and application clients may use the Java Foundation Classe

Code Example 3.4

Java Client Code for Sending a Binary Request Code Example 3.5 illustrates how a Java servlet might listen for requests from the Java client: public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException { /* Interpret the request. */ DataInputStream in = new DataInputStream(req.getInputStream()); int com

Code Example 3.5

Java Servlet Code for Interpreting a Binary Request These examples also illustrate a substantial cost of HTTP-based messaging in general; you have to write code for parsing and interpreting messages. Unfortu-nately, writing such code, especially for multiple programmable clients, can be time-consuming and error-prone. Java technologies for XML alle

3.4.4 Managing Conversational State

Whereas browser clients require a robust server-side mechanism for maintaining session state, Java clients can manage session state on their own, because they can cache and manipulate substantial amounts of state in memory. Consequently, Java clients have the ability to work while disconnected, which is beneficial when latency is high or when each

3.5 Summary

The J2EE platform supports a range of client devices and client programming models. Supported devices include desktop systems, laptops, palmtops, cell phones, and various emerging non-traditional devices. The supported programming models include browser clients using HTML and JavaScript, browser plug-in clients such as Flash, office suite clients s

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