Hibernate mapping exception

Question

I am getting the below error on trying to save an Employee object to database:

org.hibernate.MappingException: Unknown entity: com.example.common.Employee
    at org.hibernate.impl.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:597)
    at org.hibernate.impl.SessionImpl.getEntityPersister(SessionImpl.java:1339)

Dependencies in pom.xml related to hibernate [Mine is a Spring-Hibernate project]**

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate</artifactId>
    <version>3.2.7.ga</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-entitymanager</artifactId>
    <version>4.3.4.Final</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-validator</artifactId>
    <version>5.1.0.Final</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-orm</artifactId>
    <version>3.2.2.RELEASE</version>
</dependency>

I used to define Hibernate mappings in mapping XML file. With this example, I was trying with annotations.

Employee.java [only the beginning portion of code]

I am including the import statements too

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.validation.Valid;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;

import org.hibernate.validator.constraints.NotEmpty;

@Entity
@Table(name = "employees")
public class Employee implements Serializable {
    private static final long serialVersionUID = 5468763051360122059L;

    @Id
    @Column(name = "employee_guid", length = 36)
    @NotNull
    @Size(min = 36, max = 36)
    private String id;

    @Column(name = "is_active", nullable = false)
    private boolean isActive;

    @ManyToMany(mappedBy = "employees", fetch = FetchType.LAZY, cascade = {
            CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH, CascadeType.DETACH
    })

I tried changing @Enitiy to @org.hibernate.annotations.Entity too, but of no use.

Please give me some hint on where I am wrong. Please let me know if you need more code.

Edit:

Let me know how to specify Employee Entity bean here?

<bean id="MyHibernateSessionFactory"
        class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="mappingResources">
            <!-- if there is a mapping file like Employee.hbm.xml i can refer here, but i manage thru annotations -->
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.hbm2ddl.auto">create</prop>
                <prop key="hibernate.connection.autocommit">false</prop>
                <prop key="hibernate.connection.isolation">2</prop>
                <prop key="hibernate.transaction.auto_close_session">true</prop>
                <prop key="hibernate.current_session_context_class">managed</prop>
                <prop key="hibernate.transaction.flush_before_completion">true</prop>
                <prop key="hibernate.dialect">org.hibernate.dialect.H2Dialect</prop>
            </props>
        </property>
    </bean>

I am trying with this one

<property name="annotatedClasses">
            <list>
                <value>com.example.Employee</value>
            </list>
        </property>

Also changed : class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">

Update:

This question is incomplete unless more code is shared. Hence closing this for now, with the below suggestion as answer, though it is not the exact answer I was looking for. Will reopen when I get a chance. Thanks all.

Answer 1

An hibernate entity must define a no argument constructor.

Source: http://coding.tocea.com/java/java-frameworks/hibernate/hibernate-entity-does-not-define-no-argument-constructor/

Answer 2

In addition to annotations, you need to let Hibernate know about your entity classes. I think there are two ways of doing this:

1) Add the class to your hibernate.cfg.xml file:

<hibernate-configuration>
  <session-factory>
    <mapping class="com.example.common.Employee" />
  </session-factory>
</hibernate-configuration>

2) Configure Hibernate in code:

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

private static SessionFactory buildSessionFactory() {
  Configuration configuration = new Configuration();
  configuration.configure();
  configuration.addAnnotatedClass(Employee.class);
  ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()).buildServiceRegistry();
  return configuration.buildSessionFactory(serviceRegistry);
}