JSP vs Servlets

Compare JSP and Servlets directly - how Servlets generate HTML from Java, how JSP embeds Java in HTML, and when to use each.

Introduction

Servlets and JSP solve the same broad problem - generating dynamic web content in Java - but they approach it from opposite directions. A Servlet is Java code that produces HTML. A JSP page is HTML that contains Java code. Understanding this reversal is the key to knowing when to reach for each one.

Servlets: Java Generating HTML

A Servlet is a plain Java class that extends HttpServlet and overrides methods like doGet() or doPost() to handle incoming HTTP requests. Any HTML the Servlet wants to send back must be built manually, usually with a PrintWriter and repeated calls to println() or write().

GreetingServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class GreetingServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String name = request.getParameter("name");

        out.println("<html>");
        out.println("<body>");
        out.println("<h1>Hello, " + name + "!</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}

HTML sent to browser for a request like /greet?name=Asha

Click Run to see what this code prints.

This works fine for small amounts of markup, but imagine a full page with a navigation bar, a table of 50 rows, a footer, and CSS classes - every single line would need its own println() call, buried inside Java control-flow logic. That quickly becomes unreadable and painful to maintain.

JSP: HTML Embedding Java

JSP flips the arrangement. You write the page mostly as plain HTML, and drop in short pieces of Java exactly where dynamic values are needed.

greeting.jsp

<%@ page import="javax.servlet.http.HttpServletRequest" %>
<html>
<body>
    <h1>Hello, <%= request.getParameter("name") %>!</h1>
</body>
</html>

HTML sent to browser for the same request

Click Run to see what this code prints.

Both examples produce nearly identical output, but the JSP version is far easier to read as a web page, and far easier for someone comfortable with HTML but less comfortable with Java to edit safely.

Side-by-Side Comparison

Aspect	Servlet	JSP
Primary content	Java code	HTML markup
Output HTML written by	println()/write() calls	Static markup, untouched
Best suited for	Request handling, business logic, control flow	Presenting/formatting the response
Readability of large pages	Poor - HTML buried in Java	Good - HTML stays readable
Compiled by developer or container	Developer compiles the .java file	Container translates & compiles automatically
Typical role in MVC	Controller	View

When to Use Each

The rule of thumb enterprise Java teams settled on years ago is simple: use a Servlet for logic and control flow, use JSP for presentation.

Use a Servlet When

You need to process form submissions, talk to a database, validate input, manage sessions, or decide which page to show next.

Use JSP When

You need to display data as HTML - tables, forms, formatted text - once the logic has already been handled elsewhere.

Using Them Together

In real applications, Servlets and JSP are almost always used together, not as competitors. A common flow looks like this: a Servlet receives the request, performs any necessary logic (like querying a database), stores the results as a request attribute, and then forwards the request to a JSP page that only handles displaying that data.

Servlet forwarding to a JSP view

request.setAttribute("username", "Asha");
request.getRequestDispatcher("/welcome.jsp").forward(request, response);

This separation - Servlet as controller, JSP as view - is exactly the classic MVC pattern mentioned in the previous lesson, and it is the pattern most enterprise JSP applications are built around.

Common Mistakes

Avoid These Mistakes

Putting heavy business logic and database calls directly inside a JSP file instead of a Servlet.
Building large HTML pages entirely inside a Servlet using println() calls.
Treating JSP and Servlets as competing technologies rather than complementary ones.
Forgetting that request.getRequestDispatcher(...).forward(...) is how control typically passes from Servlet to JSP.

Best Practices

Keep Servlets focused on logic: reading input, talking to services/databases, deciding what to show.
Keep JSP focused on presentation: looping over data and formatting it as HTML.
Pass data from Servlet to JSP using request attributes, then read them with Expression Language in the JSP.
If a JSP page starts needing complex Java logic, that is usually a sign the logic belongs in a Servlet instead.

Frequently Asked Questions

Is JSP better than Servlets?

Neither is universally "better" - they are designed for different jobs. JSP is better for presentation, Servlets are better for logic and control flow.

Can a Servlet return JSON instead of HTML?

Yes. Servlets can write any content type, including JSON, since you control the output directly. JSP is specifically oriented toward producing HTML-like markup.

Do I have to choose only one of JSP or Servlets in a project?

No, and in practice you should not. Most real JSP applications use both together, with Servlets as controllers and JSP pages as views.

Which one should I learn first?

Many learners find it useful to see a basic Servlet first to understand HTTP request handling, then move to JSP to see how presentation is cleaner when separated out.

Key Takeaways

Servlets are Java code that generates HTML output manually.
JSP is HTML markup with small pieces of embedded Java for dynamic sections.
Servlets are best for logic and control flow; JSP is best for presentation.
Real applications typically combine both: Servlet as controller, JSP as view.
RequestDispatcher.forward() is the standard way to move from a Servlet to a JSP page.

Summary

Servlets and JSP are two sides of the same coin: one optimized for logic, the other for presentation. Knowing when to use each - and how to combine them - is fundamental to writing clean Java web applications. Next, you will set up an actual JSP development environment using Apache Tomcat so you can start running these examples yourself.

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