Java.Servlet.What are Java Server Pages (JSP)?

Posted on 29.04.2025 by Stanislav_Panteleev

Java Server Pages (JSP) are server-side technologies used to create dynamic web pages by embedding Java code directly into HTML.

  • JSPs are like HTML pages, but with the ability to run Java code inside them.
  • The server compiles JSPs into servlets behind the scenes.
  • They are mainly used for building the view layer (UI) in web applications.

In simple terms:

  • A JSP file is mostly HTML with some special tags or code blocks where you can write Java.
  • When a client (browser) requests a JSP page, the server converts the JSP into a servlet (a Java class).
  • The servlet executes the Java code and generates HTML to send back to the browser.

Purpose of JSP:

  • Simplify the process of writing server-side web pages compared to writing servlets manually.
  • Separate the presentation layer (HTML/UI) from business logic (Java code).
  • Allow designers (who know HTML) and developers (who know Java) to work together more easily.

Main Features:

  • Direct embedding of Java code using special syntax like <% Java code %>.
  • JSP Expressions to insert values directly into the output, e.g., <%= variable %>.
  • JSP Directives to control page settings, e.g., <%@ page language="java" %>.
  • JSP Actions to interact with JavaBeans or include other files, e.g., <jsp:useBean>, <jsp:include>.
  • Tag Libraries (JSTL) allow you to avoid Java code in JSPs and write cleaner, tag-based pages.

Typical Life Cycle of a JSP:

  1. First Request: JSP is translated into a servlet.
  2. Servlet Compilation: The generated servlet is compiled into a .class file.
  3. Servlet Loading: The servlet is loaded into memory.
  4. Request Processing: For each client request, the servlet’s service() method is called.
  5. Response Generation: The servlet writes the HTML output back to the client.

Example:

Simple JSP Page (greeting.jsp):

<html>
  <body>
    <h1>Hello, <%= request.getParameter("name") %>!</h1>
  </body>
</html>

If you visit greeting.jsp?name=Stanley, the server would return:

<html>
  <body>
    <h1>Hello, Stanley!</h1>
  </body>
</html>

Why Use JSP?

  • Faster and easier development of server-side UI compared to plain servlets.
  • Easy access to Java classes, beans, and libraries.
  • Built-in support for session management, database connectivity, etc.
  • Integration with MVC frameworks like Spring MVC, Struts, or JSF.

Shortcomings:

  • Mixing Java and HTML can lead to messy code if not used carefully.
  • Modern applications often prefer templating engines (like Thymeleaf, Freemarker) or front-end frameworks (React, Angular) instead of JSP.
  • JSP is old but still used in some legacy systems.
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