Question

Lines \(29-38\) of class TipTestMIDIet specify the servlet URL and the Welcomeserv1et URL. This approach can be problematic if a network administrator changes either URL. In practice, we would like the application descriptor file to contain the servlet URL and the MIDP-device user to specify the WelcomeServlet URL with the MIDP-device keypad. a) Encode the servlet URL - http: / / 10calhost : 8080/advjhtp1/-in the TipTestMIDIet application descriptor file by typing Servlet-URL : http: / / localhost : 8080 /advjhtp1/ at the end of TipTestMIDlet's . jad file. In TipTestMIDlet, use method get AppProperty of class MIDlet to return the servlet URL. (Method getAppProperty takes a property-tag string-e.g., "Servlet-URL"-as an argument and returns the string associated with that property.) b) Enable the user to specify the we1comeservlet URL. Modify the class TipTest- MIDIet constructor to create mainscreen (line 51 ) as a TextBox -a Screen subclass that enables the user to input text. A rext Box constructor takes four arguments: 1) a string that represents the TextBox's title; 2 ) a string that represents the TextBox's initial contents; 3 ) an int that represents the maximum number of characters allowed in the TextBox; 4 ) an input constraint int that specifies the required input format-e.g., if you want the user to enter a phone number, the constraint is TextField .PHONENUMBER. We want the user to enter a URL, so the constraint is TextField. URL. Use method getstring of class TextBox to return the TextBox's contents (user input) to store the We1comeServlet URL when the user presses the Select soft button.

Short answer

Add servlet URL to .jad file, use `getAppProperty` to retrieve it, and use `TextBox` to input WelcomeServlet URL.

Step-by-step solution

Encode Servlet URL in Application Descriptor

Navigate to the end of the `TipTestMIDlet's` .jad file and add the line: `Servlet-URL: http://localhost:8080/advjhtp1/` This line encodes the servlet URL in the application descriptor, allowing it to be accessed at runtime.

Retrieve Servlet URL in MIDlet

In the `TipTestMIDlet` class, use the `getAppProperty` method of the `MIDlet` class to retrieve the servlet URL. Add the following code line in your MIDlet class: `String servletURL = getAppProperty("Servlet-URL");` This line retrieves the URL associated with the "Servlet-URL" property tag specified in the .jad file.

Create TextBox for WelcomeServlet URL

Modify the `TipTestMIDlet` constructor around line 51 to create a `TextBox` for user input. The `TextBox` allows the user to type the WelcomeServlet URL via the MIDP-device keypad: ``` TextBox mainScreen = new TextBox("Enter WelcomeServlet URL:", "", 256, TextField.URL); ``` This code creates a `TextBox` titled "Enter WelcomeServlet URL:" with a maximum of 256 characters, allowing only URL input types.

Store User Input from TextBox

To store the WelcomeServlet URL when the user presses the select button, use the `getString()` method of the `TextBox` class. Add the following code when handling the 'select' command: ``` String welcomeServletURL = mainScreen.getString(); ``` This code captures the user's input from the `TextBox` and stores it in a string variable for further use.

Key concepts

Application Descriptor

An application descriptor is a crucial component of MIDlet programming. It is a configuration file, usually with a `.jad` extension, that contains metadata about your MIDlet. This file specifies various attributes like the name, version, and vendor of the application. It can also include custom properties that your MIDlet might need at runtime. In our context, we encoded the servlet URL into the application descriptor to dynamically retrieve it during execution.
This is done by adding a line such as `Servlet-URL: http://localhost:8080/advjhtp1/` to the descriptor file. When your application runs, it can use this information to establish a connection without hardcoding URLs directly into the code. This practice is particularly beneficial when URLs change frequently, as it prevents the need for constant code updates.

TextBox

A `TextBox` in MIDlet programming is a user interface element that allows text entry from the user. It is a subclass of `Screen`, and provides a simple way to collect textual data such as URLs, numbers, or general text inputs.
To create a `TextBox`, you use its constructor which requires four parameters:

• A title for the `TextBox` - a string that appears at the top of the input field.
• Initial contents - a string that appears when the `TextBox` is first displayed, usually left empty for the user to fill in.
• The maximum number of characters allowed - an integer value specifying how much text can be entered.
• An input constraint - an integer that defines what type of input is acceptable; in our exercise, we use `TextField.URL` to restrict input to URLs.

This makes `TextBox` extremely useful for capturing user input in a controlled and specific manner.

Servlet URL retrieval

Retrieving the servlet URL is an essential operation in MIDlet applications when URLs are stored in the application descriptor file. Using URLs from this file allows the application to operate with a degree of flexibility, particularly when network configurations change.
The retrieval process involves the `getAppProperty` method from the `MIDlet` class. By passing a string key, such as "Servlet-URL", to this method, you can retrieve the corresponding value stored in the application descriptor file.
This method returns the servlet's URL as a string that can then be used within the application to perform network operations. By relying on the application descriptor for such information, the application avoids hardcoded values and becomes more adaptable to changes.

User input handling

Handling user input is a critical aspect of interactive applications like those developed with MIDlet. In our scenario, we need to collect a URL from the user, which is achieved through a `TextBox`.
Once the `TextBox` is displayed, the user inputs their data using the MIDP-device keypad. After the user presses the "Select" command, the application can retrieve this data using the `getString` method of the `TextBox` class. This method provides the input as a string, which can then be processed or stored for use within the application.
Proper handling of user inputs ensures that the application can effectively respond to user needs, improve user interaction, and capture necessary data accurately and efficiently. This approach can apply to various types of input constraints, which allows for more specialized input scenarios beyond simple text.