Spring Framework - JPA Examples

import com.logicbig.example.Customer;
import org.springframework.beans.factory.annotation.Autowired;

import javax.annotation.PostConstruct;
import javax.persistence.EntityManager;
import javax.persistence.Query;
import java.util.List;

public class JpaCustomerDao implements Dao<Customer> {
    @Autowired
    private EntityManager entityManager;


    @PostConstruct
    private void postConstruct() {
        //just populate some test data if it's first time
        try {
            if (loadAll().size() == 0) {
                DataUtil.createTestData().forEach(this::saveOrUpdate);
            }
        } catch (Exception e) {
            DataUtil.createTestData().forEach(this::saveOrUpdate);
        }
    }


    @Override
    public void saveOrUpdate(Customer customer) {
        entityManager.getTransaction().begin();
        entityManager.persist(customer);
        entityManager.getTransaction().commit();
    }


    @Override
    public Customer load(long id) {
        Query query = entityManager.createQuery(
                "SELECT t FROM Customer where t.id = :id");
        query.setParameter("id", id);
        List resultList = query.getResultList();
        if (resultList.size() > 0) {
            return (Customer) resultList.get(0);
        }
        return null;
    }

    @Override
    public List<Customer> loadAll() {
        Query query = entityManager.createQuery(
                "SELECT t FROM Customer t");
        return query.getResultList();
    }
}

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Customer {

    @Id
    @GeneratedValue
    private long customerId;

    private String name;
    private String address;
    private String phone;
    //other details

    public long getCustomerId() {
        return customerId;
    }

    public void setCustomerId(long customerId) {
        this.customerId = customerId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Customer customer = (Customer) o;
        return customerId == customer.customerId;
    }

    @Override
    public int hashCode() {
        return (int) (customerId ^ (customerId >>> 32));
    }

    @Override
    public String toString() {
        return "Customer{" +
                "customerId='" + customerId + '\'' +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                ", phone='" + phone + '\'' +
                '}';
    }
}