Ajax is not a technology, It is a collection of technologies. It is used for creation a fast and dynamic web pages.
Before the Ajax, for accessing any data from the server side, it compulsory to reload whole page on client side. Ex, if the user submits a form with information, it takes more time to validate and returns response to the client. With the help of Ajax, you can update a part of web page, instead of reloading whole page.
Struts2 use a toolkit called Dojo. It provides Ajax support. Ajax allows the developers to develop GUI like web applications.
Note: If a client send a Ajax request, the server does not know it is script request, it woks another request.
Ajax is the combination of different technologies, which works together. These technologies are tools are as follows..