In Criteria API distinct clause can be applied by using following method of CriteriaQuery:

 CriteriaQuery<T> distinct(boolean distinct);

Quick example:

    CriteriaQuery<String> query = .......
    Root<Employee> employee = query.from(Employee.class);
    query.select(employee.get(Employee_.name))
         .distinct(true);

Example

Entity

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private double salary;
    private String dept;
    .............
}

Applying distinct clause

public class ExampleMain {
    private static EntityManagerFactory entityManagerFactory =
            Persistence.createEntityManagerFactory("example-unit");

    public static void main(String[] args) {
        try {
            persistEmployees();
            findDistinctDepts();
            findDistinctSalaries();
            findDistinctDeptAndSalaries();
        } finally {
            entityManagerFactory.close();
        }
    }

    public static void persistEmployees() {
        Employee employee1 = Employee.create("Diana", 2000, "IT");
        Employee employee2 = Employee.create("Rose", 4500, "Admin");
        Employee employee3 = Employee.create("Denise", 2000, "Admin");
        Employee employee4 = Employee.create("Mike", 4000, "IT");
        Employee employee5 = Employee.create("Linda", 4500, "Sales");
        EntityManager em = entityManagerFactory.createEntityManager();
        em.getTransaction().begin();
        em.persist(employee1);
        em.persist(employee2);
        em.persist(employee3);
        em.persist(employee4);
        em.persist(employee5);
        em.getTransaction().commit();
        System.out.println("-- employee persisted --");
        CriteriaQuery<Employee> query = em.getCriteriaBuilder()
                                          .createQuery(Employee.class);
        query.select(query.from(Employee.class));
        em.createQuery(query).getResultList().forEach(System.out::println);
        em.close();
    }

    private static void findDistinctDepts() {
        System.out.println("-- Distinct dept --");
        EntityManager em = entityManagerFactory.createEntityManager();
        CriteriaQuery<String> query = em.getCriteriaBuilder()
                                        .createQuery(String.class);
        Root<Employee> employee = query.from(Employee.class);
        query.select(employee.get(Employee_.dept))
             .distinct(true);
        TypedQuery<String> tq = em.createQuery(query);
        List<String> resultList = tq.getResultList();
        resultList.forEach(System.out::println);
    }

    private static void findDistinctSalaries() {
        System.out.println("-- Distinct salaries order by salary desc --");
        EntityManager em = entityManagerFactory.createEntityManager();
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Double> query = cb.createQuery(Double.class);
        Root<Employee> employee = query.from(Employee.class);
        query.select(employee.get(Employee_.salary))
             .orderBy(cb.desc(employee.get(Employee_.salary)))
             .distinct(true);
        TypedQuery<Double> tq = em.createQuery(query);
        List<Double> resultList = tq.getResultList();
        resultList.forEach(System.out::println);
    }

    private static void findDistinctDeptAndSalaries() {
        System.out.println("-- Distinct dept and salaries order by dept asc and salary desc --");
        EntityManager em = entityManagerFactory.createEntityManager();
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Object[]> query = cb.createQuery(Object[].class);
        Root<Employee> employee = query.from(Employee.class);
        query.multiselect(employee.get(Employee_.dept), employee.get(Employee_.salary))
             .orderBy(cb.asc(employee.get(Employee_.dept)), cb.desc(employee.get(Employee_.salary)))
             .distinct(true);
        TypedQuery<Object[]> tq = em.createQuery(query);
        List<Object[]> resultList = tq.getResultList();
        resultList.forEach(arr -> System.out.println(Arrays.toString(arr)));
    }
}

-- employee persisted --
Employee{id=1, name='Diana', salary=2000.0, dept='IT'}
Employee{id=2, name='Rose', salary=4500.0, dept='Admin'}
Employee{id=3, name='Denise', salary=2000.0, dept='Admin'}
Employee{id=4, name='Mike', salary=4000.0, dept='IT'}
Employee{id=5, name='Linda', salary=4500.0, dept='Sales'}
-- Distinct dept --
IT
Sales
Admin
-- Distinct salaries order by salary desc --
4500.0
4000.0
2000.0
-- Distinct dept and salaries order by dept asc and salary desc --
[Admin, 4500.0]
[Admin, 2000.0]
[IT, 4000.0]
[IT, 2000.0]
[Sales, 4500.0]

Example Project

Dependencies and Technologies Used:

• h2 1.4.197: H2 Database Engine.
• hibernate-core 5.3.2.Final: Hibernate's core ORM functionality.
  Implements javax.persistence:javax.persistence-api version 2.2
• hibernate-jpamodelgen 5.3.2.Final: Annotation Processor to generate JPA 2 static metamodel classes.
• JDK 1.8
• Maven 3.5.4