How to retrieve value from web.xml in Servlet?

I need to retrieve init-param value from xml to Servlet i used following code

<servlet><servlet-name>LoginServlet</servlet-name><servlet-class>LoginServlet</servlet-class><init-param><param-name>jdbcDriver</param-name><param-value>com.mysql.jdbc.Driver</param-value></init-param></servlet>

servlet code

public void init(ServletConfig config) throws ServletException {    super.init(config);    System.out.println(config.getInitParameter("jdbcDriver"));}

But It displayed null .. could any one help me to do that .thanks in advance