JPA/Criteria API - Like & equal problem

Perhaps you need

criteria.add(cb.like(emp.<String>get("name"), p));

because first argument of like() is Expression<String>, not Expression<?> as in equal().

Another approach is to enable generation of the static metamodel (see docs of your JPA implementation) and use typesafe Criteria API:

criteria.add(cb.like(emp.get(Employee_.name), p));

(Note that you can't get static metamodel from em.getMetamodel(), you need to generate it by external tools).

Better: predicate (not ParameterExpression), like this :

List<Predicate> predicates = new ArrayList<Predicate>();
if(reference!=null){
    Predicate condition = builder.like(root.<String>get("reference"),"%"+reference+"%");
    predicates.add(condition);
}