if (con == null) {
            try {
                Context ctx = new InitialContext();
                String dbName = (String) ctx.lookup("java:comp/env/DBName");
                String dbConnection = (String) ctx.lookup("java:comp/env/DBConnection");
                String dbUser = (String) ctx.lookup("java:comp/env/DBUser");
                String dbPassword = (String) ctx.lookup("java:comp/env/DBPassword");

                Class.forName(dbName);
                con = DriverManager.getConnection(dbConnection, dbUser, dbPassword);
            } catch (ClassNotFoundException | SQLException | NamingException | NullPointerException ex) {
                System.err.println(ex.getMessage());
            }
        }



<env-entry>
        <env-entry-name>DBName</env-entry-name>
        <env-entry-type>java.lang.String</env-entry-type>
        <env-entry-value>org.apache.derby.jdbc.ClientDriver</env-entry-value>
    </env-entry>
    <env-entry>
        <env-entry-name>DBConnection</env-entry-name>
        <env-entry-type>java.lang.String</env-entry-type>
        <env-entry-value>jdbc:derby://localhost:1527/lab</env-entry-value>
    </env-entry>
    <env-entry>
        <env-entry-name>DBUser</env-entry-name>
        <env-entry-type>java.lang.String</env-entry-type>
        <env-entry-value>lab</env-entry-value>
    </env-entry>
    <env-entry>
        <env-entry-name>DBPassword</env-entry-name>
        <env-entry-type>java.lang.String</env-entry-type>
        <env-entry-value>lab</env-entry-value>
    </env-entry>