Java Notes

JSP Introduction

Complete introduction to JavaServer Pages (JSP) - how JSP works, JSP lifecycle, scripting elements, implicit objects, and building dynamic web pages.

What is JSP?

JavaServer Pages (JSP) is a server-side technology that allows you to embed Java code directly within HTML pages. JSP simplifies the creation of dynamic web content by separating presentation (HTML) from business logic (Java).

Behind the scenes, every JSP page is converted to a Servlet by the JSP container.

How JSP Works — Behind the Scenes

1. Browser requests page.jsp │ ▼ 2. JSP Container (Tomcat) receives request │ ▼ 3. First request? → Translate JSP to Servlet (.java file) │ ▼ 4. Compile Servlet (.java → .class) │ ▼ 5. Load and instantiate Servlet │ ▼ 6. Call _jspService() method │ ▼ 7. Generate HTML response │ ▼ 8. Send response to browser

A JSP file like hello.jsp gets converted to hello_jsp.java:

java example

// Auto-generated servlet from hello.jsp
public class hello_jsp extends HttpJspBase {
    public void _jspService(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        JspWriter out = response.getWriter();
        out.write("<html>\n");
        out.write("<body>\n");
        out.write("<h1>Hello World</h1>\n");
        out.write("</body>\n");
        out.write("</html>");
    }
}

JSP Lifecycle

Phase	Method	Description
Translation	N/A	JSP → Servlet source code
Compilation	N/A	Servlet source → bytecode
Loading	N/A	Class loaded by ClassLoader
Instantiation	Constructor	Single instance created
Initialization	`jspInit()`	Called once for setup
Request Processing	`_jspService()`	Called for each request
Destruction	`jspDestroy()`	Called during shutdown

jsp example

<%-- Override lifecycle methods --%>
<%!
    public void jspInit() {
        System.out.println("JSP initialized");
    }

    public void jspDestroy() {
        System.out.println("JSP destroyed");
    }
%>

JSP Scripting Elements

1. Scriptlet `<% ... %>`

Embeds Java code that executes for each request:

jsp example

<%
    String name = request.getParameter("name");
    if (name == null) name = "Guest";
    
    java.util.Date now = new java.util.Date();
    int hour = now.getHours();
    String greeting;
    
    if (hour < 12) greeting = "Good Morning";
    else if (hour < 17) greeting = "Good Afternoon";
    else greeting = "Good Evening";
%>
<h1><%= greeting %>, <%= name %>!</h1>
<p>Server time: <%= now %></p>

2. Expression `<%= ... %>`

Outputs a value to the response (shortcut for out.print()):

jsp example

<p>Today is: <%= new java.util.Date() %></p>
<p>Your IP: <%= request.getRemoteAddr() %></p>
<p>Session ID: <%= session.getId() %></p>
<p>2 + 3 = <%= 2 + 3 %></p>

3. Declaration `<%! ... %>`

Declares instance variables and methods (added to servlet class):

Example

<%! private int visitCount = 0; private java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); private String formatDate(java.util.Date date) { return sdf.format(date); } %> <% visitCount++; %> Page visited <%= visitCount %> times Formatted time: <%= formatDate(new java.util.Date()) %>

4. Comment `<%-- ... --%>`

Example

<%-- This is a JSP comment — NOT sent to browser --%>

JSP Implicit Objects

JSP provides 9 built-in objects available without declaration:

Object	Type	Description
`request`	HttpServletRequest	Client request data
`response`	HttpServletResponse	Server response
`out`	JspWriter	Output stream
`session`	HttpSession	User session
`application`	ServletContext	Application context
`config`	ServletConfig	Servlet configuration
`pageContext`	PageContext	Page scope access
`page`	Object	Current servlet instance
`exception`	Throwable	Error (in error pages only)

Using Implicit Objects

Example

<%@ page language="java" contentType="text/html" %> <html> <body> <h2>Implicit Objects Demo</h2>  Request Method: <%= request.getMethod() %> Client IP: <%= request.getRemoteAddr() %>  Session ID: <%= session.getId() %> Username: <%= session.getAttribute("username") %>  Server Info: <%= application.getServerInfo() %> Context Path: <%= application.getContextPath() %>  <% out.println("Written using out object"); %>  Servlet Name: <%= config.getServletName() %> </body> </html>

JSP Directives

Page Directive

jsp example

<%@ page language="java" 
         contentType="text/html;charset=UTF-8"
         pageEncoding="UTF-8"
         import="java.util.*, java.text.*"
         session="true"
         isThreadSafe="true"
         errorPage="error.jsp"
         isErrorPage="false" %>

Include Directive (Static include at translation time)

jsp example

<%@ include file="header.jsp" %>
<h1>Main Content</h1>
<%@ include file="footer.jsp" %>

Taglib Directive

jsp example

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>

Complete JSP Example: User Registration

register.jsp

jsp example

<%@ page language="java" contentType="text/html;charset=UTF-8" %>
<%@ page import="java.util.*" %>
<!DOCTYPE html>
<html>
<head><title>Registration</title></head>
<body>
    <h2>User Registration</h2>
    
    <%-- Show errors if any --%>
    <%
        String error = (String) request.getAttribute("error");
        if (error != null) {
    %>
        <p style="color: red;"><%= error %></p>
    <% } %>
    
    <form action="register" method="POST">
        <label>Name:</label><br>
        <input type="text" name="name" required><br><br>
        
        <label>Email:</label><br>
        <input type="email" name="email" required><br><br>
        
        <label>Password:</label><br>
        <input type="password" name="password" required><br><br>
        
        <label>City:</label><br>
        <select name="city">
            <option value="Mumbai">Mumbai</option>
            <option value="Delhi">Delhi</option>
            <option value="Bangalore">Bangalore</option>
        </select><br><br>
        
        <button type="submit">Register</button>
    </form>
</body>
</html>

success.jsp

jsp example

<%@ page language="java" contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html>
<body>
    <h2>Registration Successful!</h2>
    <p>Welcome, <%= session.getAttribute("username") %>!</p>
    <p>Email: <%= session.getAttribute("email") %></p>
    <p>City: <%= session.getAttribute("city") %></p>
    <a href="dashboard.jsp">Go to Dashboard</a>
</body>
</html>

JSP Action Tags

jsp example

<%-- Include another page at runtime --%>
<jsp:include page="header.jsp">
    <jsp:param name="title" value="Home Page" />
</jsp:include>

<%-- Forward to another page --%>
<jsp:forward page="login.jsp">
    <jsp:param name="message" value="Please login first" />
</jsp:forward>

<%-- Use JavaBeans --%>
<jsp:useBean id="user" class="com.example.User" scope="session" />
<jsp:setProperty name="user" property="name" value="John" />
<jsp:setProperty name="user" property="*" />  <%-- auto-populate from request --%>
<p>Name: <jsp:getProperty name="user" property="name" /></p>

Common Mistakes

Putting business logic in JSP — Use servlets for logic, JSP for view only
Using scriptlets in modern apps — Use EL and JSTL instead
Not setting page encoding — Character corruption issues
Declaring variables in scriptlets that should be in declarations — Scope confusion
Forgetting that JSP becomes a servlet — Debug by looking at generated code

Interview Key Points

JSP is translated into a Servlet by the container
JSP lifecycle: Translation → Compilation → Init → Service → Destroy
9 implicit objects: request, response, out, session, application, config, pageContext, page, exception
Scriptlet <% %>, Expression <%= %>, Declaration <%! %>
<%@ page %>, <%@ include %>, <%@ taglib %> are directives
Modern JSP uses EL (${expr}) and JSTL instead of scriptlets

Summary

In this chapter, we learned about JSP Introduction in detail. Here are the key points:

Basic introduction to the concept and why it is needed
Syntax and structure with complete examples
Internal working and best practices
Real-world applications and use cases
Common mistakes and how to avoid them
How this topic is asked in interviews

To practice these concepts, write and run the code in your IDE and verify the output. Modify each example and experiment so that you deeply understand the concept.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for JSP Introduction.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, servlets, jsp, introduction

Continue learning this concept

Servlets JSPServlet IntroductionComplete introduction to Java Servlets covering web development basics, HTTP protocol, servlet architecture, deployment descriptors, and how servlets work in Java EE web applications.Servlets JSPCookies in ServletsComplete guide to handling cookies in Java Servlets - creating, reading, modifying, deleting cookies, cookie attributes, and security best practices.Servlets JSPExpression Language (EL)Complete guide to JSP Expression Language (EL) - syntax, operators, implicit objects, accessing beans, collections, and EL functions for clean JSP development.Servlets JSPGenericServletUnderstanding GenericServlet abstract class in Java - protocol-independent servlet implementation, methods, and comparison with HttpServlet.Servlets JSPHttpServletComplete guide to HttpServlet class - HTTP-specific servlet implementation with doGet, doPost, doPut, doDelete methods and practical examples.Servlets JSPJSP Tags and JSTLComplete guide to JSP tags including standard actions, JSTL core tags, formatting tags, SQL tags, custom tags, and tag files for building maintainable JSP applications.

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Java Notes

JSP Introduction

Complete introduction to JavaServer Pages (JSP) - how JSP works, JSP lifecycle, scripting elements, implicit objects, and building dynamic web pages.

What is JSP?

Behind the scenes, every JSP page is converted to a Servlet by the JSP container.

How JSP Works — Behind the Scenes

A JSP file like hello.jsp gets converted to hello_jsp.java:

java example

// Auto-generated servlet from hello.jsp
public class hello_jsp extends HttpJspBase {
    public void _jspService(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        JspWriter out = response.getWriter();
        out.write("<html>\n");
        out.write("<body>\n");
        out.write("<h1>Hello World</h1>\n");
        out.write("</body>\n");
        out.write("</html>");
    }
}

JSP Lifecycle

Phase	Method	Description
Translation	N/A	JSP → Servlet source code
Compilation	N/A	Servlet source → bytecode
Loading	N/A	Class loaded by ClassLoader
Instantiation	Constructor	Single instance created
Initialization	`jspInit()`	Called once for setup
Request Processing	`_jspService()`	Called for each request
Destruction	`jspDestroy()`	Called during shutdown

jsp example

<%-- Override lifecycle methods --%>
<%!
    public void jspInit() {
        System.out.println("JSP initialized");
    }

    public void jspDestroy() {
        System.out.println("JSP destroyed");
    }
%>

JSP Scripting Elements

1. Scriptlet `<% ... %>`

Embeds Java code that executes for each request:

jsp example

<%
    String name = request.getParameter("name");
    if (name == null) name = "Guest";
    
    java.util.Date now = new java.util.Date();
    int hour = now.getHours();
    String greeting;
    
    if (hour < 12) greeting = "Good Morning";
    else if (hour < 17) greeting = "Good Afternoon";
    else greeting = "Good Evening";
%>
<h1><%= greeting %>, <%= name %>!</h1>
<p>Server time: <%= now %></p>

2. Expression `<%= ... %>`

Outputs a value to the response (shortcut for out.print()):

jsp example

<p>Today is: <%= new java.util.Date() %></p>
<p>Your IP: <%= request.getRemoteAddr() %></p>
<p>Session ID: <%= session.getId() %></p>
<p>2 + 3 = <%= 2 + 3 %></p>

3. Declaration `<%! ... %>`

Declares instance variables and methods (added to servlet class):

Example

4. Comment `<%-- ... --%>`

Example

<%-- This is a JSP comment — NOT sent to browser --%>

JSP Implicit Objects

JSP provides 9 built-in objects available without declaration:

Object	Type	Description
`request`	HttpServletRequest	Client request data
`response`	HttpServletResponse	Server response
`out`	JspWriter	Output stream
`session`	HttpSession	User session
`application`	ServletContext	Application context
`config`	ServletConfig	Servlet configuration
`pageContext`	PageContext	Page scope access
`page`	Object	Current servlet instance
`exception`	Throwable	Error (in error pages only)

Using Implicit Objects

Example

JSP Directives

Page Directive

jsp example

<%@ page language="java" 
         contentType="text/html;charset=UTF-8"
         pageEncoding="UTF-8"
         import="java.util.*, java.text.*"
         session="true"
         isThreadSafe="true"
         errorPage="error.jsp"
         isErrorPage="false" %>

Include Directive (Static include at translation time)

jsp example

<%@ include file="header.jsp" %>
<h1>Main Content</h1>
<%@ include file="footer.jsp" %>

Taglib Directive

jsp example

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>

Complete JSP Example: User Registration

register.jsp

jsp example

<%@ page language="java" contentType="text/html;charset=UTF-8" %>
<%@ page import="java.util.*" %>
<!DOCTYPE html>
<html>
<head><title>Registration</title></head>
<body>
    <h2>User Registration</h2>
    
    <%-- Show errors if any --%>
    <%
        String error = (String) request.getAttribute("error");
        if (error != null) {
    %>
        <p style="color: red;"><%= error %></p>
    <% } %>
    
    <form action="register" method="POST">
        <label>Name:</label><br>
        <input type="text" name="name" required><br><br>
        
        <label>Email:</label><br>
        <input type="email" name="email" required><br><br>
        
        <label>Password:</label><br>
        <input type="password" name="password" required><br><br>
        
        <label>City:</label><br>
        <select name="city">
            <option value="Mumbai">Mumbai</option>
            <option value="Delhi">Delhi</option>
            <option value="Bangalore">Bangalore</option>
        </select><br><br>
        
        <button type="submit">Register</button>
    </form>
</body>
</html>

success.jsp

jsp example

<%@ page language="java" contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html>
<body>
    <h2>Registration Successful!</h2>
    <p>Welcome, <%= session.getAttribute("username") %>!</p>
    <p>Email: <%= session.getAttribute("email") %></p>
    <p>City: <%= session.getAttribute("city") %></p>
    <a href="dashboard.jsp">Go to Dashboard</a>
</body>
</html>

JSP Action Tags

jsp example

<%-- Include another page at runtime --%>
<jsp:include page="header.jsp">
    <jsp:param name="title" value="Home Page" />
</jsp:include>

<%-- Forward to another page --%>
<jsp:forward page="login.jsp">
    <jsp:param name="message" value="Please login first" />
</jsp:forward>

<%-- Use JavaBeans --%>
<jsp:useBean id="user" class="com.example.User" scope="session" />
<jsp:setProperty name="user" property="name" value="John" />
<jsp:setProperty name="user" property="*" />  <%-- auto-populate from request --%>
<p>Name: <jsp:getProperty name="user" property="name" /></p>

Common Mistakes

Putting business logic in JSP — Use servlets for logic, JSP for view only
Using scriptlets in modern apps — Use EL and JSTL instead
Not setting page encoding — Character corruption issues
Declaring variables in scriptlets that should be in declarations — Scope confusion
Forgetting that JSP becomes a servlet — Debug by looking at generated code

Interview Key Points

JSP is translated into a Servlet by the container
JSP lifecycle: Translation → Compilation → Init → Service → Destroy
9 implicit objects: request, response, out, session, application, config, pageContext, page, exception
Scriptlet <% %>, Expression <%= %>, Declaration <%! %>
<%@ page %>, <%@ include %>, <%@ taglib %> are directives
Modern JSP uses EL (${expr}) and JSTL instead of scriptlets

Summary

In this chapter, we learned about JSP Introduction in detail. Here are the key points:

Basic introduction to the concept and why it is needed
Syntax and structure with complete examples
Internal working and best practices
Real-world applications and use cases
Common mistakes and how to avoid them
How this topic is asked in interviews

To practice these concepts, write and run the code in your IDE and verify the output. Modify each example and experiment so that you deeply understand the concept.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for JSP Introduction.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, servlets, jsp, introduction

Continue learning this concept

PreviousHttpServlet NextJSP Tags and JSTL

What is JSP?

How JSP Works — Behind the Scenes

JSP Lifecycle

JSP Scripting Elements

1. Scriptlet <% ... %>

2. Expression <%= ... %>

3. Declaration <%! ... %>

4. Comment <%-- ... --%>

JSP Implicit Objects

Using Implicit Objects

JSP Directives

Page Directive

Include Directive (Static include at translation time)

Taglib Directive

Complete JSP Example: User Registration

register.jsp

success.jsp

JSP Action Tags

Common Mistakes

Interview Key Points

Summary

Continue learning this concept

What is JSP?

How JSP Works — Behind the Scenes

JSP Lifecycle

JSP Scripting Elements

1. Scriptlet <% ... %>

2. Expression <%= ... %>

3. Declaration <%! ... %>

4. Comment <%-- ... --%>

JSP Implicit Objects

Using Implicit Objects

JSP Directives

Page Directive

Include Directive (Static include at translation time)

Taglib Directive

Complete JSP Example: User Registration

register.jsp

success.jsp

JSP Action Tags

Common Mistakes

Interview Key Points

Summary

Continue learning this concept

1. Scriptlet `<% ... %>`

2. Expression `<%= ... %>`

3. Declaration `<%! ... %>`

4. Comment `<%-- ... --%>`

1. Scriptlet `<% ... %>`

2. Expression `<%= ... %>`

3. Declaration `<%! ... %>`

4. Comment `<%-- ... --%>`