Development mode of JSP learning

JSP Development mode （ Four patterns ）

 

 

JSP Program development modes include JSP Programming 、JSP+JavaBean Programming 、JSP+JavaBean+Servlet Programming 、MVC Pattern .

pure JSP Programming

stay JSP In programming mode , By applying the JSP Script flags in , Can be directly in JSP Various functions are realized in the page . Although this model is easy to implement , however , Its disadvantages are also very obvious . Because most of Java Code and the HTML Code mixed up , It will bring many difficulties to the maintenance and debugging of the program , And it is difficult to clarify the complete program structure .

This is like planning and managing a large enterprise , If all employees responsible for different tasks are arranged to work together , It is bound to cause chaos in the company 、 Difficult to manage and many other hidden dangers . So , pure JSP Page programming mode cannot be applied to large-scale applications 、 Medium or even small JSP Web In application development .

JSP+JavaBean Programming

JSP+JavaBean The programming mode is JSP Classic program development Design patterns One of , Suitable for the development of small or medium-sized websites . utilize JavaBean technology , It can easily complete some business logic operations , For example, database connection 、 User login and logout, etc .

JavaBean Is a person who follows certain rules Java class , In the development of the program , Encapsulate the business logic to be carried out into this class , stay JSP On the page , This class is called through the action tag , To execute the business logic . At this time JSP In addition to the control of some processes , It is mainly used for page display , and JavaBean Is responsible for the processing of business logic .

It can be seen that ,JSP+JavaBean The design pattern has a relatively clear program structure , stay JSP The initial stage of Technology , This model has been widely used .

chart 1 Represents the process of processing the client's request in this mode , The relevant instructions are as follows .

1. The user requests the server through the client browser .
2. The server calls after receiving the user request. JSP page .
3. stay JSP Call in page JavaBean.
4. stay JavaBean Connect and operate the database in , Or implement other business logic .
5. JavaBean Return the result of execution to JSP+ page .
6. The server reads JSP Content in page （ Combine static content with dynamic content in the page ）.
7. The server returns the final result to the client browser for display .

 

chart 1 JSP+JavaBean Design patterns

JSP+JavaBean+Servlet Programming

JSP+JavaBean Although the design pattern has separated the business logic of the website from the display page , But in this mode JSP Not only to control most of the processes in the program , But also responsible for the display of the page , So it is still not an ideal design pattern .

stay JSP+JavaBean Add... Based on the design pattern Servlet To implement the control layer in the program , Is a good choice . In this mode , from Servlet To execute the business logic and be responsible for the process control of the program ,JavaBean Components implement business logic , Act as a model of ,JSP Used for page display . It can be seen that , This model makes the hierarchical relationship in the program more obvious , The division of labor of each component is also very clear . chart 2 Represents the process of processing the client's request in this mode .
 

chart 2 JSP+JavaBean+Servlet Design patterns

chart 2 In the mode shown , The steps are described below .

1. The user requests the server through the client browser .
2. The server calls after receiving the user request. Servlet.
3. Servlet Call... According to the user's request JavaBean Deal with business .
4. stay JavaBean Connect and operate the database in , Or implement other business logic .
5. JavaBean Return the result Servlet, stay Servlet Save the results to the request object .
6. from Servlet Forward the request to JSP page .
7. The server reads JSP Content in page （ Combine static content with dynamic content in the page ）.
8. The server returns the final result to the client browser for display .

but JSP+JavaBean+Servlet There are also shortcomings in the model . This pattern follows MVC Design patterns ,MVC Just an abstract design concept , It breaks down the application to be developed into three separate parts ： Model （Model）、 View （View） And controller （Controller）.

Although it is used to realize MVC The techniques of design patterns may all be the same , But each company has its own MVC framework . in other words , These companies are used to realize their own MVC The technology applied by the architecture may be JSP、Servlet And JavaBean, But their process and design are different , So engineers need to spend more time understanding .

From the perspective of project development , Because you need to design MVC Format and method of data exchange between objects , So it takes more time to design the system .

Use JSP+JavaBean+Servlet Pattern for project development , You can choose an implementation MVC A ready-made framework for patterns , Develop on the basis of this framework , It can greatly save development time , You'll get twice the result with half the effort . at present , There are many ready-made MVC frame , for example Struts frame .

MVC Pattern

MVC（Model-View-Controller, Model - View - controller ） Is a programming concept , It applies to both simple and complex programs . Using this pattern , The application to be developed can be broken down into three separate parts ： Model 、 Views and controllers .

This design pattern is proposed mainly because of the code used to complete the task in the application （ Model , Also known as “ Business logic ”） Usually the relatively stable part of the program , And will be reused , The page where the program interacts with the user （ View ）, But it often changes .

If you have to change the business logic code because you need to update the page , Or write business logic code repeatedly when applying the same function in different modules , It will not only reduce the overall process of program development , And it will make the program difficult to maintain . therefore , Separate business logic code from appearance rendering , It will be easier to improve the program according to the change of requirements .MVC The model of the pattern is shown in Figure 3 Shown .
 

chart 3 MVC Models of patterns

Model（ Model ）：MVC In the pattern Model（ Model ） It refers to the code of business logic , It is the part of the application that is really used to complete the task .

View（ View ）： The view is actually the interface between the program and the user , Users can see its existence . Views can have certain functions , And shall abide by the constraints imposed on it . In the view , It should not contain code for data processing , Business logic code .

Controller（ controller ）： The controller is mainly used to control user requests and respond . It is based on the user's request , Select a model or modify a model , And decide what view to return .