Question

Write a Web application that consists of a servlet (DirectoryServlet) and several Web documents. Document index.html should be the first document the user sees. In that document, you should have a series of hyperlinks for other Web pages in your site. When clicked, each hyperlink should invoke the servlet with a get request that contains a page parameter. The servlet should obtain parameter page and redirect the request to the appropriate document.

Short answer

Create an `index.html` with links to DirectoryServlet; set DirectoryServlet to redirect based on a page parameter.

Step-by-step solution

Create Index.html

Create a file named `index.html` that serves as the entry point for the web application. This file should include hyperlinks that correspond to different web pages in your site. Each hyperlink will call your servlet and pass a parameter indicating which page to redirect to, for example: `Home`, `Contact Us`, and so on.

Set Up DirectoryServlet

Create a servlet class named `DirectoryServlet` by extending `HttpServlet`. This servlet will handle the incoming GET requests from `index.html`. Make sure to annotate it with `@WebServlet("/DirectoryServlet")` to map the URL to the servlet.

Handling GET Requests in DirectoryServlet

Override the `doGet` method in `DirectoryServlet`. In this method, use `request.getParameter("page")` to retrieve the `page` parameter from the URL query string. This parameter will be used to determine which document to redirect the user to.

Redirect Based on Page Parameter

Inside the `doGet` method, implement logic to determine which webpage to redirect to based on the `page` parameter value. Use `response.sendRedirect("filename.html")` to redirect the request. For instance, if the `page` parameter is `home`, redirect to `home.html`; if it's `contact`, redirect to `contact.html`.

Create Additional HTML Documents

Create the additional HTML documents (`home.html`, `contact.html`, etc.) that the servlet will redirect to. Each should correspond to a value that the `page` parameter might take. These files should contain the content for those specific pages, for example, information about the website for `home.html` or contact information for `contact.html`.

Key concepts

Web Application Development

Web application development is all about creating sites and applications that run on web servers. These applications can be accessed using web browsers, making them highly accessible to users worldwide. Web applications usually involve multiple components, such as HTML pages, stylesheets, and Java servlets, to deliver a seamless user experience.
This particular exercise demonstrates the development of a web app using Java Servlets, a popular server-side technology. Servlets allow programmers to extend the capabilities of web servers and are commonly used for processing form data, managing sessions, and redirecting requests.

• Java Servlets: They are Java programming language classes that process requests and create responses.
• Entry Point: In web applications, the entry point is often an HTML page where users begin their interaction.
• Hyperlinks: These are links embedded in the HTML that users click to navigate through the application.

Building a web application involves creating an intuitive structure of web documents and configuring Java servlets to manage data exchange and navigations.

HTTP GET Requests

HTTP GET requests are a type of request from a client to a server to retrieve information. When a web user clicks a link or enters a URL into their browser, they are typically making a GET request. This method requests data from a specified resource without making changes to it.
In the context of this exercise, GET requests are essential because they enable users to navigate through different pages of the web application. Users interact with hyperlinks within `index.html`, which send GET requests to the servlet with a 'page' parameter.

• GET vs. POST: GET requests retrieve data; POST requests submit data.
• URL Parameters: GET requests can pass data to the server as part of the URL, such as `?page=home`.
• Stateless: HTTP is a stateless protocol, meaning each request is independent.

GET requests in servlets are handled by overriding the `doGet` method, where the logic for processing and responding to each request is implemented.

Servlet Redirection

Servlet redirection is a process where a servlet sends a client request to a different resource. This is done typically after processing certain logic or conditions. It allows a web application to guide users dynamically to various pages based on their actions or input.
In this exercise, the `DirectoryServlet` uses redirection extensively. When a link in `index.html` is clicked, it sends a GET request with a `page` parameter indicating the desired destination page. The servlet checks this `page` parameter and uses `response.sendRedirect("destination.html")` to forward the user to the correct HTML document.

• Parameter Evaluation: The servlet evaluates the `page` parameter to decide the next page.
• Redirection Logic: Different URLs are constructed using `sendRedirect`, making it flexible for various page flows.
• Seamless Transitions: Users experience a smooth transition between pages through redirection.

Servlet redirection contributes to a dynamic user experience by directing requests to appropriate web pages and incorporating logical navigation paths.

HTML Document Structure

The structure of HTML documents is foundational in web development, defining how content is organized and presented to users. HTML uses a system of tags to indicate different types of content, such as headers, paragraphs, and links.
In the context of this exercise, `index.html` serves as the homepage. It contains hyperlinks, each pointing to a servlet invocation with parameters. The organization of this document is key to the user experience, as it controls how users navigate the web app.

• HTML Tags: Key elements like ``, `

  `, `

  `, are used to build web pages.

• Hyperlinks: Use `Link` to connect pages and invoke servlets.
• Document Structure: Begins with ``, followed by ``, and includes `` and `` sections.

HTML provides the framework for creating structured web documents, enabling clear navigation and interaction for users within a web application.