By invoking EntityManager#refresh(entity), we can synchronize the current persistence context to the underlying database. In other words, by invoking this method, we can reload the state of a managed entity instance from the database. The existing state of the entity instance is overwritten.

The refresh operation is cascaded to entities referenced by this entity if the attribute cascade=REFRESH or cascade=ALL are used (check out cascading tutorial).

If this method is invoked on the entity which is new (not yet persisted), detached, or removed , the IllegalArgumentException is thrown.

Example

The Entity

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private Integer id;
    private String name;
    private String department;

    public Employee() {
    }

    public Employee(String name, String department) {
        this.name = name;
        this.department = department;
    }
    .............
}

Persisting and refreshing

public class ExampleMain {

    public static void main(String[] args) {
        EntityManagerFactory emf =
                Persistence.createEntityManagerFactory("example-unit");
        try {
            persistEntities(emf);
            displayEntities(emf);
        } finally {
            emf.close();
        }
    }

    private static Employee persistEntities(EntityManagerFactory emf) {
        System.out.println("-- persisting employee --");
        EntityManager em = emf.createEntityManager();
        Employee employee = new Employee("Sara Dorsey", "Admin");
        em.getTransaction().begin();
        em.persist(employee);
        em.getTransaction().commit();
        em.close();

        print("Employee persisted", employee);
        return employee;
    }

    private static void displayEntities(EntityManagerFactory emf) {
        //loading all entities
        EntityManager em = emf.createEntityManager();
        Query query = em.createQuery("Select e from Employee e");
        List<Employee> list = (List<Employee>) query.getResultList();
        for (Employee employee : list) {
            //sending to ui for display
            displayEntity(employee);
            print("refreshing employee", employee);
            //now refreshing entity before doing something with it
            em.refresh(employee);
            print("after refreshing employee", employee);
        }
    }

    private static void displayEntity(Employee employee) {
        System.out.println("-- displaying employee --");
        System.out.println(employee);
        employee.setDepartment("Sales");
        print("employee modified in displayEntity()", employee);
    }


    private static void print(String msg, Object... objects) {
        System.out.printf("%s: %s%n", msg, Arrays.asList(objects));
    }
}

-- persisting employee --
Employee persisted: [Employee{id=1, name='Sara Dorsey', department='Admin'}]
-- displaying employee --
Employee{id=1, name='Sara Dorsey', department='Admin'}
employee modified in displayEntity(): [Employee{id=1, name='Sara Dorsey', department='Sales'}]
refreshing employee: [Employee{id=1, name='Sara Dorsey', department='Sales'}]
after refreshing employee: [Employee{id=1, name='Sara Dorsey', department='Admin'}]

Example Project

Dependencies and Technologies Used:

• h2 1.4.196: H2 Database Engine.
• hibernate-core 5.2.10.Final: The core O/RM functionality as provided by Hibernate.
  Implements javax.persistence:javax.persistence-api version 2.1
• JDK 1.8
• Maven 3.3.9