Question

Student.java

package Model;


import java.util.Set;

public class Student {
private int studentID;
private  String name;
private String city;
private Set<Address> AddressList;
private Set<Contact> ContactList;

public Set<Contact> getContactList() {
    return ContactList;
}

public void setContactList(Set<Contact> contactList) {
    ContactList = contactList;
}

public Set<Address> getAddressList() {
    return AddressList;
}

public void setAddressList(Set<Address> addressList) {
    AddressList = addressList;
}

public int getStudentID() {
    return studentID;
}

public void setStudentID(int studentID) {
    this.studentID = studentID;
}

public String getName() {
    return name;
}

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

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

}

Address.java

package Model;

public class Address {

private int Aid;
private String fullAddress;
//private Student student;
/*public Student getStudent() {
    return student;
}
public void setStudent(Student student) {
    this.student = student;
}*/
public int getAid() {
    return Aid;
}
public void setAid(int aid) {
    Aid = aid;
}
public String getFullAddress() {
    return fullAddress;
}
public void setFullAddress(String fullAddress) {
    this.fullAddress = fullAddress;
}
}

Contact.java

package Model;

public class Contact {
private int contactId;
private String mobileNo;

public int getContactId() {
    return contactId;
}
public void setContactId(int contactId) {
    this.contactId = contactId;
}
public String getMobileNo() {
    return mobileNo;
}
public void setMobileNo(String mobileNo) {
    this.mobileNo = mobileNo;
}



 }

Student.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Model.Student" table="Student">
    <id name="studentID" type="int">
        <column name="StudentID" />
        <generator class="identity" />
    </id>
    <property name="name" type="java.lang.String"/>
    <property name="city" type="java.lang.String"/>
    <set name="AddressList">
        <key column="studentID"/>
        <one-to-many class="Model.Address"/>        
    </set>
    <set name="ContactList">
        <key column="studentID"/>
        <one-to-many class="Model.Contact"/>        
    </set>
</class>

Address.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Model.Address" table="Address">
    <id name="Aid" type="int">
        <column name="Aid" />
        <generator class="identity" />
    </id>
    <property name="fullAddress" type="java.lang.String"/>
</class>

Contact.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Model.Contact" table="Contact">
    <id name="contactId" type="int">
        <column name="contactId" />
        <generator class="identity" />
    </id>
    <property name="mobileNo" type="java.lang.String"/>
</class>

Main method.

public static void main(String[] args)
{
    Configuration cfg=new Configuration();
    cfg.configure("hibernate.cfg.xml");
    SchemaExport se=new SchemaExport(cfg);
    se.setOutputFile("D:\\abc.sql");
    se.create(true,true);//create(boolean script, boolean export) 

    System.out.println("------------------Saving of Student--------------------");
    Student student =new Student();
    student.setName("Yograj");
    student.setCity("Nanded");
    Set<Address> addressList=new HashSet<Address>();
    Address address=new Address();
    address.setFullAddress("Chikhali Nanded");
    addressList.add(address);
    address=null;
    address=new Address();
    address.setFullAddress("karvenagar Pune");
    addressList.add(address);
    student.setAddressList(addressList);

    Set<Contact> contactList=new HashSet<Contact>();
    Contact contact=new Contact();
    contact.setMobileNo("9403330577");
    contactList.add(contact);
    contact=null;
    contact=new Contact();
    contact.setMobileNo("9890864805");
    contactList.add(contact);
    student.setContactList(contactList);

    boolean result=new StudentServices().SaveStudent(student);

    if(result)
    {
        System.out.println("------------------Save Student succ..--------------------");
    }
    else
    {
        System.out.println("------------------Saving failed--------------------");
    }

    System.out.println("------------------Student Details--------------------");
    List<Student> studentList=new StudentServices().GetStudentlist();
    for (Student stud : studentList) {
        System.out.println("Name:"+stud.getName());
        System.out.println("City:"+stud.getCity());
        for (Address add : stud.getAddressList()) {
            System.out.println("Full Address:"+add.getFullAddress());
        }
        for (Contact cont : stud.getContactList()) {
            System.out.println("Full Address:"+cont.getMobileNo());
        }
    }
    System.out.println("Execution over.");


}

StudentService.Java

package Service;

import java.util.List;

import javassist.runtime.Inner;

import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Restrictions;
import org.hibernate.sql.JoinType;

import Model.Address;
import Model.Contact;
import Model.Student;

public class StudentServices {
public boolean SaveStudent(Student student) {
    try {
        Configuration cfg = new Configuration().configure();
        SessionFactory sf = cfg.buildSessionFactory();
        Session session = sf.openSession();
        Transaction transaction = session.beginTransaction();

        session.save(student);
        for (Address add : student.getAddressList()) {
            session.save(add);

        }
        for (Contact cont : student.getContactList()) {
            session.save(cont);

        }
        transaction.commit();
        session.close();
        return true;
    } catch (HibernateException e) {
        return false;
    }
}

public List<Student> GetStudentlist() {
    try {
        Configuration cfg = new Configuration().configure();
        SessionFactory sf = cfg.buildSessionFactory();
        Session session = sf.openSession();
        Transaction transaction = session.beginTransaction();
        Criteria criteria = session.createCriteria(Student.class, "Student")
                .createAlias("Student.AddressList", "Address",JoinType.INNER_JOIN)
                .createAlias("Student.ContactList", "Contact",JoinType.INNER_JOIN);
        List<Student> studentList = criteria.list();

        transaction.commit();
        session.close();
        return studentList;
    } catch (HibernateException e) {
        return null;
    }
}
}

When i execute main method hibernate will create database and table.in all table it will store records but when i fetch records using criteria API it gives me error “org.hibernate.LazyInitializationException.”

Answer 1

In your case student.addressList and student.contactList use lazy loading. Lazy loading means, the values are not loaded together with the studentList, but only then when you access them with getAddressList()and getContactList.

Lazy loading only works as long as the session is still open. If not yet loaded components are accessed after closing the session a LazyInitializationException is thrown, as in your example.

What you are doing is:

1. in GetStudentlist: open the session
2. in GetStudentlist: load all students
3. in GetStudentlist: close the session
4. in main: for each student
5. in main: access the address list via student.getAddressList()

This throws in exception in step 5, because you access the address list, which applies to lazy loading, and the data can’t be loaded any more, because the session already was closed in step 3.

You must close the session after calling getAddressList() and getContactList(), then it works.

By the way, when you only read data as in GetStudentlist, then you do not need to begin a transaction, and you do not need to commit anything.