Bug 59825

It's difficult to determine why ServletRequest.startAsync has failed.  The stack trace of the exception can be checked, but it's not obvious which classes are relevant, particularly if you're trying to add asynchronous request processing to existing environments.

At a minimum, the message should be updated to indicate that valves need to explicitly declare support for asynchronous request processing, but ideally, the error message would explicitly list the valves, filters, and servlets that do not explicitly declare support: "Attempt to put servlet <name> into asynchronous mode has failed.  The following do not explicitly declare support for asynchronous request processing: valve <class>, ..., filter <name>, ..., servlet <name>, ..."