JSP execution model in Tomcat: How does Apache Tomcat execute a JSP (JavaServer Page) request in its servlet container architecture?

Introduction / Context:
JSP is a server-side view technology that compiles to a servlet. In servlet containers like Apache Tomcat, requests are handled within a multithreaded Java process. Understanding this execution model helps with performance tuning, thread safety, and resource management.

Given Data / Assumptions:

• Tomcat is a Java servlet/JSP container.
• JSPs are compiled into servlets automatically on first use or deployment.
• Threads are used to handle multiple simultaneous requests inside the same JVM.

Concept / Approach:

Tomcat translates a JSP into Java source for a servlet, compiles it to bytecode, loads it, and executes it within the container. Each incoming request is processed by a thread from Tomcat’s thread pool calling the servlet’s service method. This is not CGI (external process per request) nor an independent OS process per JSP; it is a method invocation within the JVM managed by Tomcat’s threading model.

Step-by-Step Solution:

Verification / Alternative check:

Observe Tomcat work directories where generated servlet code is stored; thread dumps show request-handling threads executing servlet methods, confirming the thread-based model.

Why Other Options Are Wrong:

CGI: spawns external processes, not used by Tomcat for JSPs.

Independent process: Tomcat does not spawn a process per JSP request.

None of the above: incorrect because threads are the correct mechanism.

Common Pitfalls:

Writing non-thread-safe JSP/servlet code (for example, mutable static fields); assuming per-request isolation like CGI when in fact state can be shared within the JVM process.

Final Answer:

By one of Tomcat's threads