附录A 外文原文
(出处： Malcolm Davis. Struts--an open-source MVC implementation
[J]. IBM Systems Journal, 2006,44(2):33-37.)
Struts——an open-source MVC implementation
Malcolm Davis
This article introduces Struts, a Model-View-Controller implementation that us rvlets and JavaServer Pages (JSP) technology. Struts can help you control change in your Web project and promote specialization. Even if you never implement a system with Struts, you may get some ideas for your future rvlets and JSP page implementation.
Introduction
Kids in grade school put HTML pages on the Internet. However, there is a monumental difference between a grade school page and a professionally developed Web site. The p
age designer (or HTML developer) must understand colors, the customer, product flow, page layout, browr compatibility, image creation, JavaScript, and more. Putting a great looking site together takes a lot of work, and most Java developers are more interested in creating a great looking object interface than a ur interface. JavaServer Pages (JSP) technology provides the glue between the page designer and the Java developer.
If you have worked on a large-scale Web application, you understand the term change. Model-View-Controller (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data. Struts is an MVC implementation that us Servlets 2.2 and JSP 1.1 tags, from the J2EE specifications, as part of the implementation. You may never implement a system with Struts, but looking at Struts may give you some ideas on your future Servlets and JSP implementations.
Model-View-Controller (MVC)
JSP tags solved only part of our problem. We still have issues with validation, flow control, and updating the state of the application. This is where MVC comes to the rescue.
MVC helps resolve some of the issues with the si英国比斯特
ngle module approach by dividing the problem into three categories:
∙Model
The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.
∙View
The view provides the prentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the tters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur.
∙Controller
The controller reacts to the ur input. It creates and ts the model.
MVC Model 2
The Web brought some unique challenges to software developers, most notably the stateless connection between the client and the rver. This stateless behavior made it difficult for the model to notify the view of changes. On the Web, the browr has to re-query the rver to discover modification to the state of the application.
Another noticeable change is that the view us different technology for implementation than the model or controller. Of cour, we could u Java (or PERL, C/C++ or what ever) code to generate HTML. There are veral disadvantages to that approach:
∙Java programmers should develop rvices, not HTML.
∙Changes to layout would require changes to code.
∙Customers of the rvice should be able to create pages to meet their specific needs.
∙The page designer isn't able to have direct involvement in page development.
∙HTML embedded into code is ugly.
For the Web, the classical form of MVC needed to change. Figure 4 displays the Web adaptation of MVC, also commonly known as MVC Model 2 or MVC 2.
Struts details
Displayed in Figure 6 is a stripped-down UML diagram of the org.apache.struts.action package. Figure 6 shows the minimal relationships among ActionServlet (Controller), ActionForm (Form State), and Action (Model Wrapper).
Figure 6. UML diagram of the relationship of the Command (ActionServlet) to the Model (Action & ActionForm)
The ActionServlet class
Do you remember the days of function mappings? You would map some input event to a pointer to a function. If you where slick, you would place the configuration information into a file and load the file at run time. Function pointer arrays were the good old days of structured programming in C.
Life is better now that we have Java technolo12月份英文
gy, XML, J2EE, and all that. The Struts Controller is a rvlet that maps events (an event generally being an HTTP post) to class. And guess what -- the Controller us a configuration file so you don_t have to hard-code the values. Life changes, but stays the same.
