This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You can enable generation of portable artifacts that allow for asynchronous client invocation by using a binding file.
Example of a binding file that enables asynchronous invocation of the operation "addNumbers" in the portType "Calculator":
When you invoke wsimport, add the -b option and specify the location of the above binding file.
In my example, the endpoint interface will look like this:
Note the two versions of the addNumbersAsync method!