Question

Please do not copy and paste an existing answer, that is not exactly correct. 9 (a) The two command buttons below produce the same navigation: Explain how these two different lines can produce the same navigation. [4 marks] (b) In JSF framework, when using h:commandButton, a web form is submitted to the server through an HTTP POST request. This does not provide the expected security features mainly when refreshing/reloading the server response in the web browser. Explain this problem and give an example. What is the mechanism that is used to solve this problem? [4 marks]

Answer 1

(a) The two command buttons can produce the same navigation by using different client-side or server-side mechanisms to achieve the desired navigation behavior.

For example, the first command button could use JavaScript code attached to an event handler to trigger a navigation action, such as changing the URL or loading a new page. The second command button could use a form submission to a server-side script or endpoint that handles the navigation logic and returns the appropriate response to the client.

In both cases, the result is the same: the user is navigated to a new location or a new page is loaded. The difference lies in the underlying implementation and the specific technologies or techniques used to achieve the navigation.

(b) In JSF (JavaServer Faces) framework, when using the h:commandButton component, a web form is submitted to the server through an HTTP POST request. This means that the form data, including user inputs, is sent to the server for processing.

The problem with this approach arises when the server responds to the POST request with a regular HTTP response, which includes the resulting webpage or data. If the user refreshes or reloads the page after the server response, the browser may re-send the previous POST request, leading to unexpected behavior. This can result in duplicate form submissions, unintended actions, or data integrity issues.

To address this problem, JSF introduces a mechanism called Post-Redirect-Get (PRG). Instead of directly rendering the response content in the POST response, the server sends a redirect response (HTTP 302) to instruct the browser to issue a new GET request for the resulting page. This way, when the user refreshes or reloads the page, the browser only repeats the GET request, avoiding the re-submission of the POST request.

By using the PRG pattern, JSF ensures that refreshing or reloading the page doesn't trigger the re-execution of the original form submission, preventing potential issues caused by duplicate submissions and maintaining a more predictable and secure user experience.