How to extend MySQLInnoDBDialect?

I want my hibernate support Mysql Text type. But i get the error:

org.hibernate.MappingException: No Dialect mapping for JDBC type: -1
at org.hibernate.dialect.TypeNames.get(TypeNames.java:56)
at org.hibernate.dialect.TypeNames.get(TypeNames.java:81)
at org.hibernate.dialect.Dialect.getHibernateTypeName(Dialect.java:370)

I search by google, I find this method is valid.

{codecitation class="brush: java; gutter: true;"}
package ceapet.jbpm;

import org.hibernate.Hibernate;
import org.hibernate.dialect.MySQLInnoDBDialect;

import java.sql.Types;

public class ExtMySQLInnoDBDialect extends MySQLInnoDBDialect {
public ExtMySQLInnoDBDialect()
{
super();
registerHibernateType(-1,Hibernate.TEXT.getName());
}
}
{/codecitation}

Than modify hibernate.xml

org.hibernate.dialect.MySQLInnoDBDialect

to

ceapet.jbpm.ExtMySQLInnoDBDialect