Hibernate Association references unmapped class when the class is mapped

I have mapped all my entity classes in my hibernate project. But still I am getting an Association references Association references unmapped class: Items. Please someone help me to solve this problem. As I am quite new to hibernate please give me a detailed answer. Thanks in advance.

Items.java

public class Items {

private long id;
private String itemId;
private double itemTotal;
private int quantity;
private Cart cart;

// no-args constructor getters and setters

Cart.java

    package com.journaldev.hibernate.model;

import java.util.Set;

public class Cart {

    private long id;
    private double total;
    private String name;
    private Set<Items> items;



     // no-args constructor getters and setters

hibernate.cfg.xml

    <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://ift.tt/UNuKEc">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/composition?zeroDateTimeBehavior=convertToNull</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">root123</property>
    <mapping resource="cart.hbm.xml"/>
    <mapping resource="Item.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

Item.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://ift.tt/UNuKEd">
<hibernate-mapping>
  <class name="com.journaldev.hibernate.model.Items" table="items">
      <id name="id" type="long">
            <column name="id" />
            <generator class="identity" />
        </id>
        <property name="itemId" type="string">
            <column name="item_id"></column>
        </property>
        <property name="itemTotal" type="double">
            <column name="item_total"></column>
        </property>
        <property name="quantity" type="integer">
            <column name="quantity"></column>
        </property>

        <many-to-one name="cart" class="Cart">
            <column name="cart_id" not-null="true"></column>
        </many-to-one>
    </class>
</hibernate-mapping>

cart.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://ift.tt/UNuKEd">
<hibernate-mapping>
  <class name="com.journaldev.hibernate.model.Cart" table="cart">
       <id name="id" type="long">
            <column name="cart_id" />
            <generator class="identity" />
        </id>
        <property name="total" type="double">
            <column name="total" />
        </property>
        <property name="name" type="string">
            <column name="name" />
        </property>
        <set name="items" table="ITEMS" fetch="select">
            <key>
                <column name="cart_id" not-null="true"></column>
            </key>
            <one-to-many class="Items"/>
        </set>
    </class>
</hibernate-mapping>

HibernateUtil.java

package com.journaldev.hibernate.util;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

public class HibernateUtil {

    private static SessionFactory sessionFactory;

    private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            Configuration configuration = new Configuration();
            configuration.configure("hibernate.cfg.xml");
            System.out.println("Hibernate Configuration loaded");

            /* ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
            System.out.println("Hibernate serviceRegistry created");

            SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);

             */

            sessionFactory = new Configuration().configure().buildSessionFactory();
            return sessionFactory;
        }
        catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            ex.printStackTrace();
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        if(sessionFactory == null) sessionFactory = buildSessionFactory();
        return sessionFactory;
    }
}

HibernateOneToManyMain.java

package com.journaldev.hibernate.main;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

import com.journaldev.hibernate.model.Cart;
import com.journaldev.hibernate.model.Items;
import com.journaldev.hibernate.util.HibernateUtil;

public class HibernateOneToManyMain {

    public static void main(String[] args) {

        Cart cart = new Cart();
        cart.setName("MyCart");

        Items item1 = new Items("I1", 10, 1, cart);
        Items item2 = new Items("I2", 20, 2, cart);
        Set<Items> itemsSet = new HashSet<Items>();
        itemsSet.add(item1); itemsSet.add(item2);

        cart.setItems(itemsSet);
        cart.setTotal(10*1 + 20*2);

        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction tx = null;
        try{
        //Get Session
        sessionFactory = HibernateUtil.getSessionFactory();
        session = sessionFactory.getCurrentSession();
        System.out.println("Session created");
        //start transaction
        tx = session.beginTransaction();

        //Save the Model objects
        session.save(cart);
        session.save(item1);
        session.save(item2);

        //Commit transaction
        tx.commit();
        System.out.println("Cart ID="+cart.getId());

        }catch(Exception e){
            System.out.println("Exception occured. "+e.getMessage());
            e.printStackTrace();
        }finally{
            if(!sessionFactory.isClosed()){
                System.out.println("Closing SessionFactory");
                sessionFactory.close();
            }
        }
    }

}