How does jsp work?

The full name of JSP is Java Server Pages, which is basically a simplified Servlet. A dynamic web technology standard. It implements the java extension in Html syntax (in the form of ). JSP, like Servlet, is executed on the server side.

What is the working principle of jsp?

Combined with the flow chart given above:

(The working principle of B/S architecture)

When the client browser (browser) requests a JSP page from the server (server), after the server receives the request, it first Check whether the requested JSP file content (code) has been updated, or whether it is the first time the JSP file is accessed after it was created:

If so, then this JSP file will be in the server-side JSP The engine converts it into a Java source code file of the Servlet class.

Next, this Servlet class will be compiled into a bytecode file under the action of the Java compiler, and loaded into the jvm (java virtual machine) for interpretation and execution.

The rest is equivalent to the Servlet processing process.

If the content (code) of the requested JSP file has not been modified, then its processing process is also equivalent to that of a Servlet. That is, the server directly retrieves the corresponding Servlet instance for processing.

It should be noted that the JSP file is not converted into the Servlet class when the server is started. Instead, the conversion may only occur when it is accessed by the client (for example, if the content of the JSP file has not been updated, Servlet conversion will no longer occur).

As far as Tomcat is concerned, open the directory %Tomcat%/work/%your project file directory%, and then you will see that there are 3 subdirectories inside: org/apache/jsp. If there are no these 3 directories, It means that the JSP file of the project has not been accessed. If you open it and go to the jsp directory, you will see some *_jsp.java and *_jsp.class files. This is the source file and bytecode file that the JSP file is converted into the Servlet class. .

If you are interested, you can use a browser to access the JSP in the server, and then observe the timing of JSP conversion to Servlet and compilation.

In short, when the container gets the JSP, it will convert it into a servlet class source file (.java), and then compile the source file into a java servlet class. In other words, JSP is essentially a servlet.

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