How to get SlingScriptHelper in servlet in CQ5.5

Hi,

I am unable to get SlingScriptHelper in servlet using the below code..

bundleContext = FrameworkUtil.getBundle(SlingScriptHelper.class).getBundleContext();
factoryRef = bundleContext.getServiceReference(SlingScriptHelper.class.getName());
sling= (SlingScriptHelper) bundleContext.getService(factoryRef);

and 

SlingBindings bindings = (SlingBindings) req.getAttribute(SlingBindings.class.getName());

SlingScriptHelper scriptHelper = bindings.getSling();

I am getting null.

java.lang.NullPointerException: Specified service reference cannot be null.

Please help me..

Thanks & Regards,

Veeru