Java Unit 4: JSP and Servlet Notes – Easy Explanations with Examples

 

Java unit 4 notes

Unit 4

Java

Q1: What are JavaServer Pages (JSP) technology? JavaServer Pages (JSP) is a server-side technology used to create dynamic web pages. It allows embedding Java code inside HTML, enabling interaction with databases and web services. JSP simplifies web development by separating presentation from business logic.

 

Q2: How do you pass control from one JSP page to another?

Control passes between JSP pages using RequestDispatcher with forward() or include() methods, or by using response.sendRedirect() for client-side redirection. These methods help navigate or share resources between pages during request processing.

 

Q3: How to pass information from JSP to included JSP?

You can pass information from a JSP to an included JSP using request attributes with request.setAttribute(). The included JSP retrieves these using request.getAttribute(), enabling data sharing within the same request scope.

 

Q4: How many JSP scripting elements are there and what are they?

There are three JSP scripting elements:

1.  Scriptlet (<% ... %>) — Java code block,

2.  Expression (<%= ... %>) — outputs value,

3.  Declaration (<%! ... %>) — declares variables/methods.

 

Q5: Explain include directive and include action of JSP?

Include directive (<%@ include file="..." %>) inserts content at translation time (static). Include action (<jsp:include page="..." />) inserts content at request time (dynamic), allowing updates without recompiling the main JSP.

 

Q6: How can you set a cookie in JSP?

In JSP, create a Cookie object with name and value, then add it to the response using response.addCookie(cookie). This sends the cookie to the client browser for storage and later retrieval.

 

Q7: What is a Servlet?

A servlet is a Java program that runs on a server, handling client requests and generating dynamic web content. It extends server capabilities by processing HTTP requests and responses, typically used in web applications for backend logic.

 

Q8: What are the advantages of using Servlets over CGI?

Servlets are faster, use fewer resources, support multithreading, maintain session better, and are platform-independent. Unlike CGI, servlets don’t create a new process for each request, making them more efficient and scalable for web applications.

 

Q9: Which package provides interfaces and classes for writing servlets?

The javax.servlet package provides the core interfaces and classes for writing servlets. Additionally, javax.servlet.http offers HTTP-specific servlet classes for handling HTTP requests and responses.

 

Q10: What is the Servlet interface?

The Servlet interface defines methods (init(), service(), destroy()) that all servlets must implement. It provides the basic contract for servlet lifecycle and request handling, enabling web servers to communicate with servlets.

 

Q11: Explain Servlet Lifecycle? Servlet lifecycle includes:

1.  Loading and Instantiation by container,

2.  Initialization via init() method,

3.  Request Handling through service() method,

4.  Termination with destroy() method to release resources.

 

Short answer

 

Q1: What is the difference between JSP and Servlets?

 

JSP (JavaServer Pages) is a server-side technology that allows embedding Java code directly within HTML pages to create dynamic web content, mainly focusing on the presentation layer. Servlets are Java classes that handle client requests and generate responses programmatically, focusing more on business logic and control. JSP is easier for designing the view, while servlets are better for controlling application flow. JSP compiles into servlets internally, combining both for dynamic web development.

 

Q2: In case of JSP, what could be the default executable method inside the generated servlet?

 

In JSP, the default executable method inside the generated servlet is the _jspService() method. This method handles each request sent to the JSP page, processing input and generating the response. Unlike the standard service() method in servlets, _jspService() is automatically generated by the JSP container and cannot be overridden by developers. It combines the Java code and HTML from the JSP, serving as the core method to handle client requests in the generated servlet.

 

Q3: What is the difference between getAttribute() and getParameter()?

 

getParameter() retrieves data sent by the client through HTTP request parameters (like form inputs or query strings), always returning strings. It's used to get user input.

getAttribute() retrieves objects stored in request, session, or application scope by the server during request processing. It returns an object, not a string, and is used for passing data between server components.

 

ChatGPT said:

Q4: What is the difference between Servlet session and JSP session?

 

Servlet session and JSP session both refer to the same HTTP session object used to track user interactions across multiple requests. In servlets, the session is accessed via HttpServletRequest.getSession(). In JSP, the session object is available by default as an implicit object named session. Both manage user data during a session, but JSP simplifies access by providing the session object automatically, while servlets require explicit retrieval. Functionally, they are the same.

 

Q5: How can one JSP communicate with a Java file?

 

A JSP can communicate with a Java file (like a Java class or bean) by creating objects of the Java class within the JSP using <%! %>, <% %>, or JSP standard actions like <jsp:useBean>. The JSP can then call methods of that Java class to perform business logic or data processing. This separation helps keep the JSP focused on presentation, while Java files handle the backend logic.

 

ChatGPT said:

Q6: What is the scriptlet tag in JSP?

 

The scriptlet tag in JSP is <% ... %>, used to embed Java code directly within an HTML page. Code inside scriptlet tags is inserted into the servlet’s _jspService() method during JSP compilation. This allows dynamic content generation and logic execution on the server side. However, heavy use of scriptlets is discouraged for maintainability; JSP Expression Language (EL) and JSTL are preferred for cleaner separation of logic and presentation.

 

Q7: How does HTTP servlet handle client requests?

 

An HTTP servlet handles client requests through its service() method, which is called by the servlet container. The service() method determines the request type (GET, POST, etc.) and calls the corresponding method (doGet(), doPost(), etc.). These methods process the request, perform business logic, and generate a response by writing to the HttpServletResponse object. This mechanism allows handling different HTTP methods separately while managing client-server communication efficiently.

 

Q8: Describe the steps to write a servlet with example?

 

Steps to write a servlet:

1.  Create a class that extends HttpServlet.

2.  Override doGet() or doPost() methods to handle requests.

3.  Use HttpServletRequest to get client data and HttpServletResponse to send output.

4.  Compile the servlet and deploy it in a servlet container (like Tomcat).

5.  Map the servlet URL in web.xml or using annotations.

Example snippet:

java CopyEdit

public class MyServlet extends HttpServlet {     protected void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {       res.getWriter().println("Hello from Servlet");  

  }  

} 

 

Q9: Write a short note on Servlet Interface,

GenericServlet, and HttpServlet

 

The Servlet interface is the base interface for all servlets, defining essential methods like init(), service(), and destroy() for lifecycle management.

GenericServlet is an abstract class that implements the Servlet interface and provides a framework for protocol-independent servlets. It simplifies development by handling common tasks.

HttpServlet is a subclass of GenericServlet, designed specifically for HTTP protocol. It provides methods like doGet() and doPost() to handle HTTP requests and is most commonly used in web applications.