Question

State whether each of the following is true or false. If false, explain why. a) Servlets usually are used on the client side of a networking application. b) Servlet methods are executed automatically. c) The two most common HTTP requests are get and put. d) The well-known port number for Web requests is 55 e) Cookies never expire. f) Httpsessions expire only when the browsing session ends or when the invalidate method is called. g) The Httpsession method getAttribute returns the object associated with a particular name.

Short answer

a) False, b) True, c) False, d) False, e) False, f) False, g) True.

Step-by-step solution

Evaluate Statement a

Servlets are designed to run on the server side of a networking application, not on the client side. Therefore, the statement is false.

Evaluate Statement b

Servlet methods, particularly the service method, are automatically executed when a servlet is invoked in response to client requests. Therefore, the statement is true.

Evaluate Statement c

The two most common HTTP requests are GET and POST, not PUT. Therefore, this statement is false. PUT is used less frequently, primarily for uploading data to the server.

Evaluate Statement d

The well-known port number for Web requests, specifically HTTP, is 80, not 55. Therefore, the statement is false.

Evaluate Statement e

Cookies can be set with an expiration date, and they can expire when the set date is reached or when the browser session ends if no expiration date is set. Hence, this statement is false.

Evaluate Statement f

HTTP sessions can expire based on server settings or session inactivity, not just when the browsing session ends or when invalidate is called. Therefore, this statement is false.

Evaluate Statement g

The HttpSession method getAttribute indeed returns the object associated with a particular name. Therefore, this statement is true.

Key concepts

HTTP Requests

HTTP Requests form a fundamental part of web communication, enabling the interaction between clients (like web browsers) and servers. Every time you type a web address or click a link, an HTTP request is sent to a web server. There are several types of HTTP requests, but the most common ones you will encounter are GET and POST.

• GET: This request is used to retrieve data from a server at the specified resource. It's a read-only operation, so it doesn't change any data on the server.
• POST: This request is used to send data to a server to create or update resources. It often submits form data and causes some data change on the server.

It's essential to understand these requests as they dictate how data is transmitted over the web. They essentially act as the vehicles for transporting that data back and forth. This data exchange makes dynamic web applications possible, such as shopping carts and search engines.

Client-Server Architecture

This architecture is a core concept in web development, describing how servers and clients interact through networks. In a typical client-server model, the client sends requests, and the server processes those requests and provides responses.

• Client: This is typically a web browser or mobile app that interacts with the server. When you access a website, your browser acts as a client.
• Server: This part handles requests for data and services. It performs tasks like hosting web pages, storing data, and processing application business logic.

Over time, multiple requests can be handled, and with technologies like Java Servlets, servers can efficiently process these requests using methods like service(). Understanding this architecture is critical for developing web applications that smoothly connect users and servers.

Cookie Expiration

Cookies are small files that websites store on a user's browser to remember information, like login details or shopping cart contents. An important feature of cookies in web development is their expiration.

Cookies can have an expiration date, determining how long they are stored by the browser:

• Session cookies: These are temporary cookies that expire once the browser is closed. They are typically used for session management.
• Persistent cookies: These have a set expiration date thus remain on the user's device after closing the browser. They are used for remembering preferences or maintaining logged-in status on returning visits.

By setting an expiration date, web developers can control the duration of data persistence, enhancing user experience by automating logins, or ensuring that user preferences are remembered.

HttpSession Management

HttpSession management is crucial for tracking user sessions in web applications. It allows developers to store user-specific data across multiple requests and interactions within a session. A session begins when the user starts interacting with an application and finishes when the session times out.

• Session tracking: This is achieved using identifiers for each user's session, allowing unique identification of individuals.
• Expiration: Sessions can expire based on time settings on the server. Inactivity often triggers expiration to free up server resources.

Managing HttpSessions is vital in scenarios where consistent state maintenance is required, such as shopping carts on e-commerce websites, ensuring users do not lose data as they navigate across different pages or step away briefly.