PROBLEM

Post/Redirect/Get (PRG) is a common design pattern for web applications, to help avoid duplicate form submissions and allow web applications to behave more intuitively with browser bookmarks and the reload button. After a web user submits a form to a server, the server typically generates an HTML page as a response. To the user, this looks like an ordinary web page, but because it was generated by an HTTP POST request, it cannot be bookmarked, and attempting to reload/refresh the page in the browser could cause the form information to be resubmitted, possibly with unexpected results (such as a duplicate purchase). Wikipedia

SOLUTION

To avoid this problem, many web applications use the PRG pattern — instead of returning an HTML page directly, the POST operation returns a redirection command (using the HTTP 303 response code (sometimes 302) together with the HTTP "Location" response header), instructing the browser to load a different page using an HTTP GET request. The result page can then safely be bookmarked or reloaded without unexpected side effects. Wikipedia

HOW IT WORKS

When a post is made to a Skyway Operation, the View is configured to send a redirect command to the browser to a second URL, using the URL mapping's redirect option. The redirect results in a second request (get) being automatically made by the end-user's browser to another URL. The second URL is mapped to an operation for loading the model data before being directed to a JSP page for rendering the view. The redirect results in the second URL being listed in the browser's address bar. If the end-user refreshes the page, the original data won't be resubmitted because only the second URL will be reloaded. If the second URL is configured with an Operation that loads data, a bookmarked page can be reconstituted.

The following fragment shows two URL mappings working in tandem to implement the PRG pattern.

URL                                        OPERATION                         VIEW 
----------------------                     ----------------------------      ---------------------------------
/MyController/SaveOperation.action  --> SaveOperation              --> edit.html (w/ REDIRECT) 
/edit.html                          --> LoadOperation              --> edit.jsp 
          

As far as the end-user is concerned, they submitted data to the application and they received a response, and they are generally unaware that two http requests were used to accomplish it.

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