confused with Page ContextType and onActivate with StreamResponse

[jqzone]

Some code like this

Page class

public class SearchUser{


        @ActivationRequestParameter(value="filer")
private String filter;
 @Inject
private IStaffService staffService;

private String staffId;
 protected void onActivate(String staffId){
this.staffId = staffId;
}
 StreamResponse onActivate(){
              JSONObject json= new JSONObject();

              return new TextStreamResponse("application/json",
json.toString());

       }

}