Servlets vs JSP

Servlet: a Java class that runs on a server (servlet container such as Tomcat), receives HTTP requests, and generates responses. It is Java code with HTML embedded in out.println().

JSP (JavaServer Pages): a text page that is HTML with Java embedded (scriptlets, expressions, JSTL, EL). The container translates a JSP into a servlet and compiles it on first request, so JSP is built on servlets.

// Servlet
public class HelloServlet extends HttpServlet {
  protected void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
    res.setContentType("text/html");
    res.getWriter().println("<h1>Hello " + req.getParameter("name") + "</h1>");
  }
}

<%-- JSP --%>
<h1>Hello <%= request.getParameter("name") %></h1>

Comparison

Basis	Servlet	JSP
Nature	Java class with HTML in strings	HTML page with Java tags
Best for	Logic, controllers, processing	Presentation, views
Ease of writing	Harder for UI; markup is hard to edit	Easier for designers; natural HTML
Compilation	Compiled manually	Auto-translated and compiled on first request
Maintenance	Changing HTML needs recompiling Java	Edit the page directly
Built-in objects	Must be obtained explicitly	Implicit objects (request, session, out)
Performance	Slightly faster on first request	First request slower (translation), then equal

Advantages and limitations

Servlets

• Advantages: full control over request handling, efficient (one thread per request), platform independent, good for controllers, filters, and APIs.
• Limitations: presentation code is cumbersome and mixes HTML into Java; designers cannot edit pages easily.

JSP

• Advantages: simple and quick UI development, easy for web designers, tag libraries (JSTL) reduce Java code, automatic recompilation.
• Limitations: heavy scriptlet logic makes pages messy and hard to debug and test; not suitable for complex business logic.

When to choose which

• Use Servlets for controllers, request processing, form handling, authentication, file upload, REST endpoints, and business logic.
• Use JSP for pages that mostly display dynamic data (views, reports, templates).
• Best practice (MVC): servlet as controller, JSP as view, JavaBeans/services as the model. The servlet processes the request, then forwards to a JSP: request.getRequestDispatcher("result.jsp").forward(req, res);