The Facebook provides a lot of integration facilities so that your website become more social ..
One of these methods is to add the LIKE button (Share button is already depreciated now); you can also enable Facebook login/authentication, ...etc.
Here is the simple code you need to add to have this Like button working fine easily..
<iframe src="http://www.facebook.com/plugins/like.php?href=<%=request.getRequestURL() %>" scrolling="no" frameborder="0" style="border:none; width:450px; height:80px"></iframe>
For more details about Facebook integration:
For more details about the Like button integration: