1. What is JSP?

JavaServer Pages (JSP) is a server-side technology used to create dynamic, data-driven web pages by inserting Java code directly into HTML, XML, or other document types.

• Purpose: Simplifies the creation of views (UI) compared to writing raw HTML strings inside Servlets.
• MVC Role: Acts primarily as the View component in classic Model-View-Controller architecture.
• Servlet Relationship: Every JSP page is automatically translated into a Java Servlet by the web container before execution.

2. JSP Lifecycle

When a client requests a JSP page, the web container manages it through five key phases:

[ JSP File ] ──► Translation ──► Compilation ──► Loading & Instantiation ──► Execution (_jspService)

• Translation: The container parses the JSP and generates equivalent Java Servlet code.
• Compilation: The generated .java servlet file is compiled into a .class bytecode file.
• Loading & Instantiation: The container loads the class and creates a servlet instance.
• Initialization (jspInit()): Called once to initialize resources.
• Execution (_jspService()): Executed for every request to process inputs and return responses.
• Destruction (jspDestroy()): Called when the page is removed from service.

3. JSP Scripting Elements

Scripting elements allow you to embed Java directly into HTML markup.

Element	Syntax	Description	Example
Scriptlet	<% ... %>	Executes arbitrary Java code	<% String user = "Sandeep"; %>
Expression	<%= ... %>	Evaluates and prints value directly to output	<%= user %>
Declaration	<%! ... %>	Declares class-level variables and methods	<%! int count = 0; %>
Directive	<%@ ... %>	Gives instructions to the JSP container	<%@ page import="java.util.Date" %>
Comment	<%-- ... --%>	Hidden server-side comment (not visible in page source)	<%-- DB logic here --%>

4. JSP Directives

Directives provide instructions to the container during translation.

Page Directive (<%@ page ... %>): Defines attributes for the entire page (imports, content type, error pages).

<%@ page contentType="text/html;charset=UTF-8" import="java.util.List" errorPage="error.jsp" %>

Include Directive (<%@ include ... %>): Merges content from another file during translation (static include).

<%@ include file="header.jsp" %>

Taglib Directive (<%@ taglib ... %>): Imports custom tag libraries like JSTL.

<%@ taglib prefix="c" uri="jakarta.tags.core" %>

5. Implicit Objects

JSP provides 9 pre-defined objects accessible directly within scriptlets and expressions without explicit declaration:

• request: The HttpServletRequest instance.
• response: The HttpServletResponse instance.
• out: The JspWriter output stream used to send response text.
• session: The HttpSession instance for user session tracking.
• application: The ServletContext shared across all users.
• config: The ServletConfig object for initialization parameters.
• pageContext: Provides access to page attributes and environment details.
• page: Reference to the current servlet instance (this).
• exception: Captures thrown errors (available only in error pages where isErrorPage="true").

6. JSP Standard Actions

JSP standard actions control behavior using XML-style tags instead of raw Java scriptlets.

<jsp:include>: Dynamically includes another resource at request time.

<jsp:include page="footer.jsp" />

<jsp:forward>: Forwards the request to another page or servlet.

<jsp:forward page="login.jsp" />

<jsp:useBean> / <jsp:setProperty> / <jsp:getProperty>: Instantiates and interacts with JavaBeans.

<jsp:useBean id="user" class="com.example.UserBean" scope="session" />

<jsp:setProperty name="user" property="username" value="Sandeep" />

<p>Welcome, <jsp:getProperty name="user" property="username" /></p>

7. Expression Language (EL) & JSTL

Modern JSP development discourages raw Java scriptlets (<% %>) in favor of Expression Language (EL) and the JSP Standard Tag Library (JSTL) to keep views clean.

Expression Language (EL): Simplified syntax (${...}) to access attributes and properties.

<!-- Replaces <%= request.getAttribute("username") %> -->

<p>Hello, ${username}</p>

JSTL (Core tags): Replaces Java loops and conditional statements with standard tags.

<%@ taglib prefix="c" uri="jakarta.tags.core" %>



<c:if test="${not empty username}">

    <h2>Welcome back, ${username}!</h2>

</c:if>



<c:forEach items="${productList}" var="item">

    <p>${item.name} - ${item.price}</p>

</c:forEach>