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This article is about how to implement event-driven technology in JSP Servlet development. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

JSP Servlet provides an excellent platform for WEB application developers. However, at present, most of the domestic JSP Servlet-based development is in the most basic state, with low code reuse rate and low development efficiency, which can not meet the requirements of large and complex WEB development.

First of all, in order to implement event-driven, MVC technology must be used in JSP Servlet development.

M=Model (Model)

V=View (View)

C=Control (control)

The view (V) defines the user interface. The model (M) defines abstract classes and logic. The control (C) is responsible for invoking the logic of the model according to the events that occur in the view to complete the business processing.

Model (model) is implemented by ordinary java classes.

View (view) is implemented by jsp.

Control (control) is implemented by servlet.

Views and models are closely related and independent of each other. A model is an abstraction of a view and must contain some logic to handle the events of the objects represented by the view. At the same time, views can be represented in a variety of ways for the same logic. For example, in web development

1) for a SingleSelection class that represents a "radio" abstraction, it can be displayed as a Radio button, a radio drop-down box, or any other radio control in the user's browser.

2) for a Submition class that represents the "submit" abstraction, it can be displayed as Submit button, hyperlinks, pictures, or even any control that triggers the submit () method of JavaScript on the user's browser.

Event-driven is extremely important for MVC technology, which is mainly implemented by Control (control). The implementation of JSP-SERVLET itself is very suitable for writing event-driven programs.

As we all know, the javax.servlet.http.HttpServlet class calls doPost (HttpServletRequest req, HttpServletResponse resp) or doGet (HttpServletRequest req, HttpServletResponse resp) every time.

Method to respond to the client's submit operation.

The event that Servlet responds to is the submit action of the client browser. The submit event of the client browser triggers the specific event handling method of Servlet, but there is only one entry: the service (HttpServletRequest req, HttpServletResponse resp) method of the javax.servlet.http.HttpServlet class. (specific to the response to the client's operation, it may be doPost (HttpServletRequest req, HttpServletResponse resp) or doGet (HttpServletRequest req, HttpServletResponse resp) method. So you can override these methods to control how Servlet responds to submit events, calling different JSP,JAVA BEAN or even EJB. For example: EventDrivenServlet inherits javax.servlet.http.HttpServlet and overrides the doPost (HttpServletRequest req, HttpServletResponse resp) and doGet (HttpServletRequest req, HttpServletResponse resp) methods so that both methods call the same method directly. We name this method "act"? void act (HttpServletRequest req, HttpServletResponse resp) act method should call the corresponding class and method based on the information passed in the req parameter, and * * return resp to the client.

The processing performed by the act method must include the following:

1) parse req.

2) initialize (or update) the corresponding class according to the parsing result of the previous step.

3) call the corresponding method for logical processing.

4) reflect the processing results in resp.

5) specify the next displayed page according to the logical processing result

6) forward to the next page.

But how does the act method know which method of which class to call and which screen to migrate to? The answer is to pass a message to the act method? Message.

The Message class is an abstraction of the message, should be defined as abstract, and can be an empty class. All concrete message classes are derived from this Message class. All message classes must inherit from the Message class.

As mentioned earlier, every submit control on the screen (JSP) logically corresponds to a Submition, and each Submition is associated with a specific message class. In this way, as long as we can intercept these message classes in the Control layer, parse the information carried by these message classes, and delegate them to the methods of the corresponding classes to handle, we can implement event-driven. Example: there is a "login" button on the screen, which corresponds to a Submition class and generates a LoginMessage message. LoginMessage inherits Message and adds a Hashtable member variable with user name and password information. There is also a "change password" button on the screen, which corresponds to a ChangePasswordSubmition class and generates a ChangePasswordMessage message. ChangePasswordMessage inherits Message and adds a Hashtable member variable with user name and password information. When Servlet responds to this submit, it can delegate processing based on the type of message and the information it carries. For implementation, we should overload the act () method of EventDrivenServlet and add a parameter of the Message class. Void act (HttpServletRequest req, HttpServletResponse resp,Message message)

If message instanceof LoginMessage is true, then the message is modeled as LoginMessage, and the LoginMessage is passed to the appropriate method. After processing, the corresponding image is specified and sent back to the client.

If message instanceof ChangePasswordMessage is true, then the message is modeled as ChangePasswordMessage, and the ChangePasswordMessage is passed to the appropriate method. After processing, the corresponding image is specified and sent back to the client.

Thank you for reading! This is the end of this article on "how to import event-driven technology in JSP Servlet development". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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