How to handle JPA unique constraint violations?

How can I find out that a unique constraint was violated?

Exception are chained, you have to call getCause() recursively to get the provider specific exception (and maybe go down to the SQLException) to translate it into something your application can handle nicely for your user. The following will print the chain of exception:

for (t = e.getCause(); t != null; t = t.getCause()) {
    logger.debug("Exception:" + t);
}

For the exception handling and the "translation", you could do something like what Spring does (see the various JpaDialect classes, e.g. HibernateJpaDialect to get an idea).

All this is not nice, this code won't be portable and finding what attribute(s) caused the violation won't be easy. This somehow confirms that there is no elegant and portable way to handle constraint violations in JPA.

You can use the following :

If you are using spring framework then you can use :

org.springframework.dao.DataIntegrityViolationException

If standard JPA following can be used

org.hibernate.exception.ConstraintViolationException

At sql level following can be used :

java.sql.SQLIntegrityConstraintViolationException