tomcat Configuring a JDBC Datasource Using a JNDI reference as a JDBC Resource in Context

Example

public void test() {
    Connection conn = null;
    Statement stmt = null;
    try {
        Context ctx = (Context) new InitialContext().lookup("java:comp/env");
        conn = ((DataSource) ctx.lookup("jdbc/SomeDataSource")).getConnection();

        stmt = conn.createStatement();
        //SQL data fetch using the connection
        ResultSet rs = stmt.executeQuery("SELECT * FROM TABLE");
        while (rs.next()) {
            System.out.println(rs.getString("Id"));
        }
        conn.close();
        conn = null;
    }
    catch(Exception e){
        e.printStackTrace();
    }
    finally {

        if (stmt != null || conn != null) try {
            assert stmt != null;
            stmt.close();
        } catch (SQLException ex) {
            // ignore -- as we can't do anything about it here
            ex.printStackTrace();
        }
    }
}