context.xml and DataSource

i'm getting "Cannot load JDBC driver class 'com.ibm.db2.jcc.DB2Driver'"
error but this code works:
working code:

String url = "jdbc:db2://localhost:50000/test";
String user = "user";
String password = "pass";
Class.forName("com.ibm.db2.jcc.DB2Driver");
Connection conn = DriverManager.getConnection(url, user, password);
<<<

context.xml:

<?xml version="1.0" encoding="UTF-8"?>
<Context path="/Test">
    <Resource name="test"
              auth="Container"
              type="javax.sql.DataSource"
              username="user"
              password="pass"
              driverClassName="com.ibm.db2.jcc.DB2Driver"
              url="jdbc:db2://localhost:50000/test"
              />
</Context>
<<<

code not working:

InitialContext ic = new InitialContext();
Context c = (Context)ic.lookup("java:comp/env");

try {
    DataSource ds = (DataSource)c.lookup("test");
    Connection connection = ds.getConnection();
} catch(Exception e) {
    // log e.getMessage();
}
<<<