How JSP works internally

The following steps explain how JSP works inside the web server:

• Client browser sends an HTTP request to the web server.
• The web server recognizes that the HTTP request is for a JSP page and forwards it to a JSP engine. This is done by using the URL or JSP page which ends with .jsp instead of .html.
• The JSP engine loads the JSP page from disk and converts it into servlet content. This conversion is very simple in which all template text is converted to println( ) statements and all JSP elements are converted to Java code that implements the corresponding dynamic behavior of the page.
• The JSP engine compiles the servlet into an executable class and forwards the original request to a servlet engine.
• A part of the web server called the servlet engine loads the Servlet class and executes it. During execution, the servlet produces an output in HTML format, which the servlet engine passes to the web server inside an HTTP response.
• The web server forwards the HTTP response to your browser in terms of static HTML content.
• Finally web browser handles the dynamically generated HTML page inside the HTTP response exactly as if it were a static page

Below image shows pictorial view of how JSP works 

Upon getting client request, JSP engine checks whether a servlet for requested JSP file already exists and whether the modification date on the JSP is older than the servlet. If the JSP is older than its generated servlet, the JSP container assumes that the JSP hasn't changed and that the generated servlet still matches the JSP's contents.

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