Ultimate JSP (Java Server Pages) Handbook and Top Interview Questions and Answers

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Introduction to JSP (Java Server Pages)

Java Server Pages (JSP) is a powerful technology used for creating dynamic, platform-independent web applications. It allows developers to embed Java code directly into HTML, making web development efficient and flexible. JSP is built on top of Java Servlets and is widely used in enterprise-level applications.

In this post, we’ll cover the basics of JSP, advanced concepts, and some of the top interview questions that will help you stand out as a candidate during Java-based interviews.

Why Use JSP?

• Separation of Concerns: JSP separates the presentation logic from the business logic, making it easier to maintain and scale web applications.
• Ease of Use: JSP allows embedding Java directly within HTML, making it intuitive for developers familiar with both technologies.
• Reusable Components: JSP tags and custom tag libraries help in reusing components across multiple pages.
• Power of Java: Since JSP is built on top of Java, it can use the full power of Java, including multithreading, database connectivity, and more.
• Faster Development: JSP simplifies web page development, speeding up the time taken to develop and deploy web applications.

Core Concepts of JSP

1. JSP Lifecycle

Understanding the JSP lifecycle is crucial for understanding how a JSP page is processed and executed. The main stages are:

• Translation Phase: The JSP page is converted into a Servlet.
• Compilation Phase: The converted Servlet is compiled into bytecode.
• Initialization Phase: The jspInit() method is called to initialize the Servlet.
• Execution Phase: The service() method processes client requests.
• Destruction Phase: The jspDestroy() method is called to clean up resources before the page is unloaded.

2. Scripting Elements

JSP allows embedding Java code using the following scripting elements:

• Declarations (<%! %>): Declare variables and methods that can be used in the JSP page.
• Scriptlets (<% %>): Embed Java code directly in the HTML code.
• Expressions (<%= %>): Output the result of a Java expression directly into the HTML response.

3. JSP Directives

JSP directives provide global settings for JSP pages:

• Page Directive: Defines page attributes.

  
  <%@ page language="java" contentType="text/html; charset=UTF-8" %>
  

• Include Directive: Includes another resource at compile time.

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

• Taglib Directive: Declares a custom tag library.

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

4. JSP Standard Tag Library (JSTL)

JSTL is a set of standard tags that simplify common tasks in JSP, such as iteration, conditionals, and internationalization. It reduces the need for Java scriptlets, keeping JSP pages clean and readable.

To use JSTL, include the JSTL library in your project and declare the taglib directive in your JSP page:

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

Key JSTL Tag Libraries

• Core Tags (<c:...>): Basic control flow tags.
• Formatting Tags (<fmt:...>): Formatting data and localization.
• SQL Tags (<sql:...>): Simplified database access.
• XML Tags (<x:...>): For working with XML data.

5. Error Handling

In JSP, you can define error pages to handle exceptions:

"<%@ page errorPage="error.jsp" %>"

In error.jsp, the exception object is available to capture and display details of the error:4

"<%= exception.getMessage() %>"

JSTL Core Tags with Examples

1. Iteration with <c:forEach>

<c:forEach> allows iteration over collections such as arrays, lists, or maps.
Example:

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

<ul>
  <c:forEach var="item" items="${itemList}">
    <li>${item}</li>
  </c:forEach>
</ul>
This will output a list of items from the itemList collection.

2. Conditional Statements with <c:if>

<c:if> allows conditional rendering of JSP content.
Example:
<c:if test="${userLoggedIn}">
  <p>Welcome back, ${username}!</p>
</c:if>
The content will only be displayed if userLoggedIn is true.

3. Default Value with <c:choose>

<c:choose> is like a switch-case statement in Java.
Example:
<c:choose>
  <c:when test="${userRole == 'admin'}">
    <p>Welcome, Admin!</p>
  </c:when>
  <c:otherwise>
    <p>Welcome, Guest!</p>
  </c:otherwise>
</c:choose>
This renders the appropriate message based on the user's role.

4. URL Parameter Handling with <c:param>

The <c:param> tag is used to add parameters to a URL.
Example:
<a href="<c:url value='/login'>">
  <c:param name="user" value="${username}" />
</a>
This will generate a URL with a query parameter for username.

Top JSP& JSTL Interview Questions and Answers

1. What is JSP? How does it differ from Servlets?

JSP (Java Server Pages) is a technology that helps in creating dynamic web pages by embedding Java code into HTML. While Servlets are Java classes that handle requests and responses, JSP is more convenient for web designers as it mixes HTML and Java in a more readable way.

2. Explain the JSP lifecycle.

The JSP lifecycle includes five phases: Translation, Compilation, Initialization, Execution, and Destruction. The JSP is first converted into a Servlet and then executed.

3. What are JSP directives?

page

4. What is the difference between <jsp:include> and <%@ include %>?

<jsp:include> 

5. What are custom tags in JSP?

Custom tags are user-defined JSP tags that encapsulate reusable functionality. 
These tags are defined in a tag library (TLD file) and used in JSP pages via the 
taglib directive.

6. What are implicit objects in JSP?

JSP provides several predefined objects known as implicit objects:
request: The HttpServletRequest object.
response: The HttpServletResponse object.
session: The session associated with the client.
out: A JspWriter object used to write output to the response.
application: The Servlet context.
config: The Servlet configuration object.

7. What is JSP Expression Language (EL)?

JSP EL simplifies accessing data stored in JavaBeans, request parameters, or session 
attributes. EL expressions start with ${} and automatically handle type conversion.
Example:
${user.name}

8. How can you prevent scriptlet code in JSP?

To make JSP pages cleaner and more maintainable, avoid using scriptlets. Instead, use JSTL 
or EL to handle logic and data processing in the presentation layer.

9. What are JSP actions?

JSP actions are XML tags that perform specific tasks. Examples include:
<jsp:include>: To include content.
<jsp:forward>: To forward a request to another page.
<jsp:useBean>: To create or locate a JavaBean instance.

10. How is JSP better than other web technologies?

JSP is platform-independent, integrates well with Java applications, and is supported by a wide range of tools and libraries, making it highly efficient for building large-scale web applications

11. What is JSTL? Why should we use it?

JSTL is a collection of standard tags that simplify JSP code. It helps avoid Java code in JSP and promotes cleaner, more readable pages.

12. What are core tags in JSTL?

JSTL core tags are used for basic operations like iteration, conditionals, and URL management.Examples include <c:forEach>, <c:if>, <c:set>, and <c:out>.

13. How do <c:forEach> and <c:if> work?

<c:forEach>

14. What are the differences between <jsp:include> and <%@ include %>?

<jsp:include>

15. What is the role of the jsp:setProperty action?

This action sets the value of a JavaBean property. It can be used to populate beans with request parameters or static values.