<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
   
        <!-- Settings for a local HSQL (testing) database. -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/dbname</property>
        <property name="connection.username">root</property>
        <property name="connection.password">password</property>

        <!-- Use the C3P0 connection pool. -->
        <property name="c3p0.min_size">3</property>
        <property name="c3p0.max_size">5</property>
        <property name="c3p0.timeout">1800</property>
   
        <!-- Disable second-level cache. -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
        <property name="cache.use_query_cache">false</property>
        <property name="cache.use_minimal_puts">false</property>
        <property name="max_fetch_depth">3</property>
   
        <!-- Print SQL to stdout. -->
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
   
        <!-- Drop and then re-create schema on SessionFactory build, for testing. -->
        <property name="hbm2ddl.auto">create</property>
   
        <!-- Bind the getCurrentSession() method to the thread. -->
        <property name="current_session_context_class">thread</property>

        <!-- Hibernate XML mapping files -->
        <mapping resource="test/TestDAO.hbm.xml"/>
    </session-factory>

</hibernate-configuration>

<?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="TestDAO" table="TST_TestDAO">
      <id name="id" column="testDAOID" type="long">
         <generator class="native" />
      </id>
      <property name="testParam" type="integer" />
   </class>
</hibernate-mapping>

public class TestServlet extends HttpServlet{
   private static final long serialVersionUID = -4475599757796846392L;

   public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      Session session = HibernateUtil.getSessionFactory().getCurrentSession();
      session.beginTransaction();
      TestDAO testDAO = new TestDAO();
      testDAO.setTestParam(5);
      session.save(testDAO);
      session.close();
      
   }
}

package test;

public class TestDAO {
   
   private Long id = null;
   
   private int testParam;
   
   public TestDAO(){
      
   }

   public Long getId() {
      return id;
   }

   public void setId(Long id) {
      this.id = id;
   }

   public int getTestParam() {
      return testParam;
   }

   public void setTestParam(int testParam) {
      this.testParam = testParam;
   }

}

public class HibernateUtil {
   
   private static final SessionFactory sessionFactory;

    static {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            sessionFactory = new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Make sure you log the exception, as it might be swallowed
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

exception

javax.servlet.ServletException: Servlet execution threw an exception

root cause

java.lang.ExceptionInInitializerError
   business_logic.HibernateUtil.<clinit>(HibernateUtil.java:17)
   business_logic.servlets.login.Login.processRequest(Login.java:42)
   business_logic.servlets.BaseServlet.doPost(BaseServlet.java:42)
   business_logic.servlets.BaseServlet.doGet(BaseServlet.java:25)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

root cause

org.hibernate.MappingException: entity class not found: TestDAO
   org.hibernate.mapping.PersistentClass.getMappedClass(PersistentClass.java:99)
   org.hibernate.tuple.PropertyFactory.getGetter(PropertyFactory.java:168)
   org.hibernate.tuple.PropertyFactory.buildIdentifierProperty(PropertyFactory.java:44)
   org.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:124)
   org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:434)
   org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:109)
   org.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:55)
   org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:226)
   org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1300)
   business_logic.HibernateUtil.<clinit>(HibernateUtil.java:13)
   business_logic.servlets.login.Login.processRequest(Login.java:42)
   business_logic.servlets.BaseServlet.doPost(BaseServlet.java:42)
   business_logic.servlets.BaseServlet.doGet(BaseServlet.java:25)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

root cause

java.lang.ClassNotFoundException: TestDAO
   org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1360)
   org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1206)
   java.lang.ClassLoader.loadClassInternal(Unknown Source)
   java.lang.Class.forName0(Native Method)
   java.lang.Class.forName(Unknown Source)
   org.hibernate.util.ReflectHelper.classForName(ReflectHelper.java:100)
   org.hibernate.mapping.PersistentClass.getMappedClass(PersistentClass.java:96)
   org.hibernate.tuple.PropertyFactory.getGetter(PropertyFactory.java:168)
   org.hibernate.tuple.PropertyFactory.buildIdentifierProperty(PropertyFactory.java:44)
   org.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:124)
   org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:434)
   org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:109)
   org.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:55)
   org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:226)
   org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1300)
   business_logic.HibernateUtil.<clinit>(HibernateUtil.java:13)
   business_logic.servlets.login.Login.processRequest(Login.java:42)
   business_logic.servlets.BaseServlet.doPost(BaseServlet.java:42)
   business_logic.servlets.BaseServlet.doGet(BaseServlet.java:25)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

<class name="test.TestDAO" table="TST_TestDAO">