<servlet>
        <servlet-name>index</servlet-name>
        <jsp-file>/index.jsp</jsp-file>
        <init-param>
            <param-name>test</param-name>
            <param-value>testValue</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>index</servlet-name>
        <url-pattern>/index</url-pattern>
    </servlet-mapping>

 <%= getServletContext().getInitParameter("test") %>
или так 
<%= application.getInitParameter("test") %>

 <%= getServletContext().getInitParameter("test") %>
или так 
<%= application.getInitParameter("test") %>