Proxy Objects and Hibernate Example 2

Proxy Object in Hibernate

     

     1)      Proxy User Class is a dynamic subset of Original User Class.

     2)      When session.get(User.class,1) is called, hibernate returns Proxy User class which pulls only ist level fields from DB . This is called lazy initialization as hibernate isn’t returning Addresses in this case.

     3)    When user.getListOfAddresses() is called, hibernate gives call to Hibernate and fetches all the addresses.

UserDetailsDTO.java

@Entity

@Table(name="USER_DETAILS")

public class UserDetailsDTO implements java.io.Serializable{

     private static final long serialVersionUID = 1L;

     @Id

     @GeneratedValue(strategy=GenerationType.AUTO)

     private int userId;

    

     @Column(name="USER_NAME")

     private String userName;

    

      @ElementCollection(fetch=FetchType.EAGER) // Collection in               hibernate

                                  @JoinTable(name="USER_ADDRESS",joinColumns=@JoinColumn(name="USER_ID"))

//To change the default TN UserDetailsDTO_listOfAddresses to                 USER_ADDRESS

     @GenericGenerator(name="hilo-gen",strategy="hilo")

     // To make an explicit    Generator for Address_Id(Primary Key)

     @CollectionId(columns={@Column(name="ADDRESS_ID")},generator="hilo-        gen",

type=  @Type(type="long"))*/

    

     // GenericGenerator and CollectionId is hibernate specific                   annotations.

     // ADDRESS_ID is a primary key in USER_ADDRESS table

     private Collection<Address> listOfAddresses= new ArrayList<>();

    

     // Changing from Set to ArrayList(Index) to add Primary Key in               Address Table

     public Collection<Address> getListOfAddresses() {

           return listOfAddresses;

     }

    

     public void setListOfAddresses(Collection<Address> listOfAddresses) {

           this.listOfAddresses = listOfAddresses;

     }

    

     /*private Set<Address> listOfAddresses = new HashSet<Address>();

    

     public Set<Address> getListOfAddresses() {

           return listOfAddresses;

     }

     public void setListOfAddresses(Set<Address> listOfAddresses) {

           this.listOfAddresses = listOfAddresses;

     }*/

    

     public int getUserId() {

           return userId;

     }

     public void setUserId(int userId) {

           this.userId = userId;

     }

     public String getUserName() {

           return userName;

     }

     public void setUserName(String userName) {

           this.userName = userName;

     }

}

Address.java

@Embeddable

@Table(name = "ADDRESS")

// It must be Table and not Entity

public class Address {

     @Column(name = "STREET")

     private String street;

     @Column(name = "BUILDING")

     private String building;

     public String getStreet() {

           return street;

     }

     public void setStreet(String street) {

           this.street = street;

     }

     public String getBuilding() {

           return building;

     }

     public void setBuilding(String building) {

           this.building = building;

     }

}

HibernateTest.java

public class HibernateTest {

     public static void main(String[] args) {

           UserDetailsDTO user =new UserDetailsDTO();

           user.setUserName("Paras");

          

           Address addr1 = new Address();

           addr1.setBuilding("722/18 Shastri Nagar, ROhtak");

           addr1.setStreet("Street number 5");

          

           Address addr2 = new Address();

           addr2.setBuilding("Kamla Nagar, New Delhi");

           addr2.setStreet("Street number 6");

          

           user.getListOfAddresses().add(addr1);

           user.getListOfAddresses().add(addr2);

          

           SessionFactory sessionFactory = new                                       Configuration().configure().buildSessionFactory();

           Session session = sessionFactory.openSession();

           session.beginTransaction();

           session.save(user);

           session.getTransaction().commit();

           session.close();

           System.out.println("WOrking till now");

           user=null;

          

           session = sessionFactory.openSession();

           user=(UserDetailsDTO) session.get(UserDetailsDTO.class,1);

           System.out.println(user.getUserName()+" " + user.getUserId());

           session.close();

           /*Below method isn't called if fetch is Lazy, it will give                  Exception as session is closed and hibernate won't be able to              make call to DB 
             For user.getListOfAddresses(), a call to DB is required and                thus session should be open if fetch is lazy(by default)*/

           System.out.println("Session CLosed");

             /* Below will start working even if session is closed when                fetch is set to be EAGER
             */

           System.out.println(user.getListOfAddresses().size());

     }

}

Output :

Hibernate: select nextval ('hibernate_sequence')
Hibernate: insert into USER_DETAILS (USER_NAME, userId) values (?, ?)
Hibernate: insert into USER_ADDRESS (USER_ID, BUILDING, STREET) values (?, ?, ?)
Hibernate: insert into USER_ADDRESS (USER_ID, BUILDING, STREET) values (?, ?, ?)
WOrking till now
Hibernate: select userdetail0_.userId as userId0_0_, userdetail0_.USER_NAME as USER2_0_0_, listofaddr1_.USER_ID as USER1_0_2_, listofaddr1_.BUILDING as BUILDING2_, listofaddr1_.STREET as STREET2_ from USER_DETAILS userdetail0_ left outer join USER_ADDRESS listofaddr1_ on userdetail0_.userId=listofaddr1_.USER_ID where userdetail0_.userId=?
Paras 1
Session CLosed

2