ExtJs is an popular java script framework. To develop rich and interactive user interface, extjs is used. It is a basically library of java script component which are ready to use in webpage.
ExtJs components work very well with JSON data. If in server side we decide to Spring as framework. Its very easy to integrate ExtJs with Spring. In Spring MVC we can easily configure FTL (free marker technology)
for specific to ExtJs Component. FTL is something which is responsible to convert java objects to desired JSON object. So there can be a generic controller in Spring, Which can be derived by other controller as per application design.
ExtJS component will talk to Spring controller which will return JSON objects.
Next thing I will try to put some code which will give a descent idea.