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JSP architecture and lifecycle

JSP (JavaServer Pages) follows the Model-View-Controller (MVC) architecture pattern, which separates the application logic (Model), presentation layer (View), and user interaction (Controller). Here is a high-level overview of the JSP architecture and lifecycle:

  1. The client sends a request to the server for a JSP page.
  2. The JSP page is first translated into a servlet by the JSP container.
  3. The translated servlet is then compiled into bytecode.
  4. The compiled servlet is loaded and executed by the JSP container to generate the HTML response.
  5. The generated HTML response is sent back to the client.

Now, let's take a look at a simple JSP example to understand the lifecycle in more detail:

First, create a new JSP file named "example.jsp". Here's the content of the file:

jsp
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<html>
   <body>
      <%
         String message = "Hello, JSP!";
         out.println(message);
      %>
   </body>
</html>

When the client sends a request to the server for the "example.jsp" page, the following steps are performed:

  • The JSP container translates the JSP page into a servlet class. The translated code might look like this:
java
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public class example_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {
    // Generated servlet code
    public void _jspService(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        JspWriter out = null;
        // Set response content type
        response.setContentType("text/html");
        // Get JSP writer
        out = _jspx_page_context.pushBody();
        // Business logic
        try {
            String message = "Hello, JSP!";
            out.println(message);
        } catch(Exception ex) {
            out.println("Exception: " + ex);
        }
        // Finalize JSP writer
        out = _jspx_page_context.popBody();
    }
}
  • The servlet class is compiled into bytecode.
  • The compiled servlet is loaded and executed by the JSP container to generate the HTML response. The output might look like this:
html
Copy code
<html>
   <body>
      Hello, JSP!
   </body>
</html>
  • The generated HTML response is sent back to the client.


Next: Basic JSP syntax

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