How to get JNDI Service in general class?

[avseq anthoy]

I want get JNDI Service provided by Tomcat , But it can't work.
Are there any wrong in my code that I need to modify?
The code listed as below.

    
public static void main(String[] args) throws Exception
    {
Connection conn = null;
Hashtable env = new Hashtable();
env.put(Context.INITIAL_CONTEXT_FACTORY,"com.sun.jndi.fscontext.RefFSContextFactory");
Context initContext = new InitialContext(env);
Context envContext = (Context) initContext.lookup("java:/comp/env");
DataSource ds = (DataSource) envContext.lookup("jdbc/mydb");
conn = ds.getConnection();
if (conn.isClosed())
    System.out.println("Connection close");
else
    System.out.println("Connection open");
    }