Now i have resolved another plugin for Struts 2 support. This plugin is called Netbeans Struts2 Plug-in and its a re-pack for the plugin i was trying to install. Though this plugin in not certified but it is working good. The developers have tested it on netbeans 7.4 but i'm using it not netbeans8 and i have not suffered any issues.
I have found another way, that is using maven. That is also a good way but i would not recommend it if you have slow internet connection.