##JPQL

JPQL stands for Java Persistence Query Language and it is a platform-independent query language. It operates on the entity metamodel, not the database schema. It is very similiar to the SQL language.

Created by the createQuery method of the EntityManager:

entityManager.createQuery("from Employee").getResultList()

Defined as a named queries using either annotations or xml.

@NamedQuery(name = "getNames", query = "select e.firstName from Employee e")

<named-query name="getNames">
    <query>select e.firstName from Employee e</query>
</named-query>

##Criteria query

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Employee> q = cb.createQuery(Employee.class);
Root<Country> e = q.from(Employee.class);
q.select(e);
TypedQuery<Employee> typedQuery = em.createQuery(q);
List<Employee> list = typedQuery.getResultList();

• javax.persistence.query.timeout - sets maximum query execution time in milliseconds. A QueryTimeoutException is thrown if timeout is exceeded.
• javax.persistence.lock.timeout - sets maximum waiting time for pessimistic locks, when pessimistic locking of query results is enabled. A LockTimeoutException is thrown if timeout is exceeded.

This hints can be set on EntityManager level:

em.setProperty("javax.persistence.query.timeout", 3000)

Or on the query itself:

query.setHint("javax.persistence.query.timeout", 5000)

Or for the whole persistence unit in persistence.xml:

<properties>
    <property name="javax.persistence.query.timeout" value="1000"/>
</properties>