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There are two main techniques for developing Web applications in Java, namely Servlets and JSPs. A servlet is a Java program executed on the server side, and a program called a servlet container (which is actually a server) is responsible for executing Java programs. The JSP (Java Server page) is a page that is executed by the JSP container .
The most important difference between servlet and JSP is that the servlet is dominated by Java programs, the output of HTML code needs to use the OUT.PRINTLN function, that is, in Java embedded HTML, and JSP is based on HTML pages, When you need to write Java code, you insert Java code directly into the page, which is embedded in the HTML. A typical example is as follows:
JSP file
Copy CodeThe code is as follows:
Servlet
It can be seen that the JSP is easy to output, while the servlet facilitates logical processing. Therefore, the practical application of the two are often used in combination, their respective roles.
And Tomcat is the servlet container and the JSP container mentioned above. The following scenarios support the SERVLET/JSP protocol for each version:
| Tomcat version | Support Servlet | Support JSP |
| 6.0.x | 2.5 | 2.1 |
| 5.5.x | 2.4 | 2.0 |
| 4.1.x | 2.3 | 1.2 |
| 3.3.x | 2.2 | 1.1 |
Structure of the Web application
After Tomcat is installed, you can look at the WebApps directory under the Tomcat directory. This directory is used to save the Web application.
The root directory is the directory that should be placed in the WebApps directory. The Web-inf directory cannot be accessed from the browser. Web-inf/classes is a compiled Java program (primarily a servlet), and Web-inf/lib is the repository file (. jar file) used by the runtime, and Web. XML is the configuration information for the entire application.
Other files, such as. JSP, pictures, JavaScript scripts, and so on, can be placed directly under the Web application's root directory.
MVC modelThe so-called MVC model is a method of separating data, logic processing and user interface.
In Java, the three parts of MVC correspond to JavaBeans, JSP, and servlet, respectively.
The picture is as follows:
Introduction to JSP and servlet description
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