Well, using POST wont help...all it will do is make a popup for the
user saying something like "Do you really want to repost the data" (or
word to that effect), and most users will just press OK.
My suggestion would be to either
a) Implement the shopping cart via ajax
or
b) have the addToCart controller issue a redirect to a page without
the parameter, that way the user can hit refresh as many times as he
likes.
The OP wants to keep the cart in view so the user can add to it at will
without excess navigation. They want the 'add' button to be active, they said.
Let's consider some analysis, then design. How likely or frequent will a
user's use of REFRESH be? It'll happen some, but not often, so we'd like a
low-cost solution, in terms of software maintenance effort.
A variation on the Synchronizer Token pattern might help. The classic pattern
prevents resubmission of form data placing a "token inside a hidden field.
Upon submission, request processing first tests for the presence of a valid
token in the request parameter by comparing it with the one registered in the
session."
<
http://www.javaworld.com/javaworld/javatips/jw-javatip136.html>
The cited article replaces the token with null to prevent any resubmission
"until a new token is saved in the session, which must be done at the
appropriate time based on the desired application flow of control." In a
variation, that appropriate time would be right away, instead of nulling the
session token.
A REFRESH will resubmit the old, no longer valid token, and the transaction
will be ignored. A new 'add' click will submit the updated token in the
hidden field, and the server will confirm it and proceed with the operation.
Benefits of this approach are that it does not add superfluously hackish
pages, it does not alter the behavior of well-known browser operations like
REFRESH or BACK except to make them safe, and it's simple.
The word for an operation that only has effect the first time it's applied is
"idempotent". I had a bank hit my debit card twice for the same transaction a
while back. They failed to make that transaction idempotent.
