Struts——an open-source MVC implementation
By: Malcolm Davis.
Source: Struts--an open-source MVC implementation[J].IBM Systems Journal
pensionThis 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 page 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 c
reating a great looking object interface than a ur interface. Java Server 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 single 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
oaaThe 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-qu我喜欢你英文
ery 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.
∙tribonCustomers of the rvice should be able to create pages to meet their specific needs. faultless
∙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.
Figure 4. MVC Model 2
Struts, an MVC 2 implementation
Struts is a t of cooperating class, rvlets, and JSP tags that make up a reusable MVC 2 design. This definition implies that Struts is a framework, rather than a library, but Struts also contains an extensive tag library and utility class that work independently of the framework. Figure 5 displays an overview of Struts.
Figure 5. Struts overview复眼是什么意思
Struts overview
∙Client browr
An HTTP request from the client browr creates an event. The Web container will respond with an HTTP respon. yours sincerely
∙Controller
The Controller receives the request from the browr, and makes the decision where to nd the request. With Struts, the Controller is a command design pattern implemented as a rvlet. l file configures the Controller.
plague∙有道网页翻译Business logic
The business logic updates the state of the model and helps control the flow of the application. With Struts this is done with an Action class as a thin wrapper to the actual business logic.
∙Model state
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The model reprents the state of the application. The business objects update the application state. ActionForm bean reprents the Model state at a ssion or request level, and not at a persistent level. The JSP file reads information from the ActionForm bean using JSP tags.
