Web application design with servlets and JSPs

王朝厨房·作者佚名  2007-01-04
窄屏简体版  字體: |||超大  

Figure 256. Web application design overview

The major parts of such a design are discussed in the sequence of the flow of

the application.

Chapter 10 Web application design with servlets and JSPs

In this chapter we present a short overview of a guideline for designing Web

applications consisting of servlets, JSPs, and JavaBeans.

Application structure

The general structure of a well-architected user interaction in a Web

application is shown in Figure 256.

HTML page

The input page for each step is either a static HTML page or a dynamic

HTML page created from a previous step. The HTML page contains one or

multiple forms that invoke a servlet for processing of the next interaction.

Input data can be validated through JavaScript in the HTML page or passed

to the servlet for detailed validation.

Servlet

The servlet gets control from the Application Server to perform basic control

of flow. The servlet validates all the data, and returns to the browser if data

is incomplete or invalid.

For valid data, processing continues. The servlet sets up and calls command

beans that perform the business logic.

The servlet initializes the view beans and registers them with the request

block so that the JSPs can find the view beans.

Depending on the results of the command beans, the servlet calls a JSP for

output processing and formatting.

Command beans

Command beans control the processing of the business logic. Business logic

may be imbedded in the command bean, or the command bean delegates

processing to back-end or enterprise systems, such as relational databases,

transaction systems (CICS, MQSeries, IMS, and so forth).

A command bean may perform one specific function, or it may contain many

methods, each for a specific task. Command beans may be called Task

Wrappers in such a case.

Results of back-end processing are stored in data beans.

Data beans

Data beans hold the results of processing that was performed by the

command bean or by back-end systems. For example, a data bean could

contain an SQL result or the communication area of a CICS transaction.

Data beans may not provide the necessary methods for a JSP to access the

data; that is where the view beans provide the function.

View beans

View beans provide the contract between the output producing JSPs and the

data beans that contain the dynamic data to be displayed in the output.

Each view bean contains one or multiple data beans and provides tailored

methods so that the JSP has access to the data stored in the data beans.

JSPs

The JSPs generate the output for the browser. In many cases that output

again contains forms to enable the user to continue an interaction with the

application.

JSPs use tags to declare the view beans. Through the view beans, the JSP

gets access to all the dynamic data that must be displayed in the output.

Model-View-Controller

This design follows the Model-View-Controller design pattern:

. The JSPs (and HTML pages) provide the view.

. The servlet is the controller.

. The command beans represent the model.

The data beans contain the data of the model, and the view beans are helper

classes to provide a data channel between the view and the model.

The servlet (controller) interacts with the model (the command beans) and

the view (the JSPs). The servlet controls the application flow.

 
 
 
免责声明:本文为网络用户发布,其观点仅代表作者个人观点,与本站无关,本站仅提供信息存储服务。文中陈述内容未经本站证实,其真实性、完整性、及时性本站不作任何保证或承诺,请读者仅作参考,并请自行核实相关内容。
 
 
© 2005- 王朝網路 版權所有 導航