Servlets, JSP, and MVC

Servlets and JavaServer Pages (JSP) are the foundational technologies for building web applications in Java. A Servlet is a Java program that runs on a web server (like Apache Tomcat) and extends the capabilities of the server. It intercepts HTTP requests from a web browser, processes them, and generates an HTTP response. Servlets are written entirely in Java, which makes them powerful for handling business logic but cumbersome for generating complex HTML content. JSP, on the other hand, is designed to simplify the creation of the presentation layer (the 'View'). A JSP file looks much like an HTML file but can contain special tags and embedded Java code (called scriptlets) that allow for dynamic content generation. Under the hood, the web server translates a JSP file into a Servlet. The Model-View-Controller (MVC) pattern is a software architectural pattern that separates the application into three interconnected components. The Model represents the application's data and business logic. The View is responsible for rendering the user interface (this is where JSP shines). The Controller (typically a Servlet) acts as the intermediary, receiving user input from the View, processing it (by interacting with the Model), and then selecting the next View to display. This separation of concerns makes the application much more organized, easier to maintain, and testable. Understanding this fundamental pattern is crucial before moving on to modern frameworks like Spring, which are built upon these same principles.