Question

State whether each of the following statements is true or false. If false, explain why. a) An Httpservlet's calls method doGet upon receiving a get request and method doPost upon receiving a post request. (true/false). b) A User-Agent header contains information about the server. (true/false). c) DocumentBuilder's static method newDocumentBuildex creates a new DocumentBu11dex. (true/false). d) In this case study, TipTestservlet uses XSLT to transform XML Tip Test Documents to well formed content for all clients. (true/false). e) The J2ME CLDC package consist of java. Ío, Java. lang and java.net. (true/ false). f) The application management software loads a MIDlet on a MIDP device. (true/false). g) The application description file specifies such information as the MIDP device's configuration and the MIDlet's name. (true/false). h) Classes Alert, Form, Screen, and List are the concrete classes of the MIDP highlevel user-interface package, (true/false). i) A javax.microedition. 1 cdu1. Command object encapsulates an action to be executed by the object that received the Command. (true/false). j) An HttpSession's Set-Cookie header field contains session information. (truc/ false).

Short answer

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

Step-by-step solution

Statement A: doGet and doPost Methods

The statement is true. When an HTTP GET request is received, the `doGet` method of an `HttpServlet` is called. Similarly, when an HTTP POST request is received, the `doPost` method is invoked. This is the standard behavior of an `HttpServlet` in handling HTTP methods.

Statement B: User-Agent Header

The statement is false. The `User-Agent` header contains information about the client, such as the browser type and operating system. It does not carry information about the server.

Statement C: newDocumentBuilder Method

The statement is false. The method name 'newDocumentBuildex' is incorrect. The correct method of `DocumentBuilderFactory` is `newDocumentBuilder`, which creates a new instance of a `DocumentBuilder`, not 'DocumentBu11dex'.

Statement D: TipTestServlet and XSLT

The statement is true in context if the described behavior is part of the case study, where `TipTestServlet` uses XSLT (eXtensible Stylesheet Language Transformations) to convert XML into a format suitable for clients.

Statement E: J2ME CLDC Packages

The statement is false. The J2ME CLDC (Connected Limited Device Configuration) package includes `java.io`, `java.lang`, and `java.util`, not `java.net`.

Statement F: Loading MIDlet on MIDP Device

The statement is true. Application management software in MIDP (Mobile Information Device Profile) devices manages the lifecycle of MIDlets, which includes loading them onto the device.

Statement G: Application Description File

The statement is true. The application description file, often known as the JAD (Java Application Descriptor) file, includes metadata such as the configuration details of the device and the name of the MIDlet.

Statement H: MIDP High-Level UI Classes

The statement is false. In the MIDP high-level user-interface, `Alert`, `Form`, `Screen`, and `List` are classes. However, `Screen` is an abstract class, not a concrete class.

Statement I: Command Object in javax.microedition

The statement is false. A `javax.microedition.lcdui.Command` object represents a command that can be performed on a user interface element, but it does not directly execute actions. The associated listeners execute these commands.

Statement J: HttpSession and Set-Cookie

The statement is false. An `HttpSession` object typically uses a `Set-Cookie` header to maintain session state by including a session identifier, not explicit session data. The actual session data is kept server-side.

Key concepts

HttpServlet

An `HttpServlet` is a Java class that handles HTTP requests in a web application running on a server. It extends the `GenericServlet` class and provides an interface for handling requests and responses over the HTTP protocol. The primary role of an `HttpServlet` is to respond to incoming requests from clients, which it does by overriding methods like `doGet` and `doPost`. These methods are executed depending on the type of request received.

When a `GET` request is made, typically to retrieve data or a webpage, the `doGet` method gets called. This method is often used for requests that do not modify content on the server. On the other hand, the `doPost` method handles `POST` requests, which are commonly used when data needs to be sent to the server for processing or storage.

Key points about `HttpServlets` include:

• Designed to support the architecture of a Java web server.
• Provides methods for handling different types of HTTP requests.
• Acts as a server-side component of web applications.
• Easily integrates with other Java technologies like JSP (JavaServer Pages).

request handling

Request handling refers to the process of receiving, processing, and responding to client requests in a web application. In Java servlets, this process is crucial because it determines the flow of data between the client and server.

When a client makes a request to a web server, it is packaged into an HTTP request and sent to the appropriate servlet. This servlet then performs several actions:

• Extracts data from the request, such as parameters and headers.
• Processes the request, which may involve accessing databases, performing computations, or invoking business logic.
• Constructs a response in the form of an HTTP response containing necessary data or a web page.

The servlet's responsibility is to efficiently handle these requests and generate the proper responses. This helps create dynamic and interactive web applications.

Servlets also provide mechanisms to handle different types of requests differently, such as using `doGet` for data retrieval and `doPost` for data submission. Additionally, servlets can manage sessions, allowing them to maintain state between client interactions.

User-Agent header

The `User-Agent` header is part of the HTTP request headers sent from the client to the server. This header contains important details about the client's environment, providing information such as:

• The browser being used (e.g., Chrome, Firefox, Safari).
• The version of the browser.
• The operating system of the client device.
• Device type, such as desktop or mobile.

By examining the `User-Agent` header, servers can tailor responses according to the client’s specifications. For instance, a server might render a different version of a webpage if it recognizes the client using a mobile browser, implementing responsive design practices to enhance user experience.

Understanding and utilizing the `User-Agent` header helps developers provide better support across diverse platforms and devices. This makes the `User-Agent` header an essential aspect of creating adaptable web applications.

MIDlet

A `MIDlet` is a type of application designed to run on mobile devices under the Mobile Information Device Profile (MIDP) as part of the Java ME (Micro Edition) platform. MIDlets are written in Java and primarily used for developing applications on mobile phones and embedded devices.

MIDlets have several defining characteristics:

• They are subject to the constraints of mobile devices, such as limited memory and processing power.
• They typically interact with users through a simpler user interface framework, compared to desktop and web applications.
• The application lifecycle is controlled by the device's application management software, which handles operations like installation, execution, and removal of MIDlets.

The creation of a MIDlet involves developing within the Java ME environment, using MIDP APIs to access device features like the user interface, data storage, and network connectivity. To distribute and run a MIDlet, developers package it in a JAR file, typically accompanied by a JAD (Java Application Descriptor) file that provides necessary metadata.

MIDlets played a significant role in the early mobile app development era, enabling the widespread deployment of Java applications on phones and other compact devices. However, with the rise of more advanced mobile OS like Android, their popularity has declined.