How to handle exception in java

Im working on spring mvc app. My problem is when I call delete method in dao by controller class, exception is not handle in dao. but if I use try catch around calling method in controller it'll catch the error.

controller class method:

customerDao.delete(id);

Rapository class:

public void delete(long id)
{
try{
em.remove(em.find(id));
}
catch(Exception e)
{
//not come to here
}
}

If I use try catch around "customerDao.delete(id);" handle error. Why I cant handle exception in dao class. Note : Exception thrown is child record found unexpectedrollbackexception