Erro com Hibernate

Estado HTTP 500 - 

--------------------------------------------------------------------------------

type Informe de Excepción

mensaje 

descripción El servidor encontró un error interno () que hizo que no pudiera rellenar este requerimiento.

excepción 

javax.servlet.ServletException: org.hibernate.MappingException: Unknown entity: br.modelo.Atributos1Nivel
	org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:286)
	org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
	org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:803)


causa raíz 

org.hibernate.MappingException: Unknown entity: br.modelo.Atributos1Nivel
	org.hibernate.impl.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:548)
	org.hibernate.impl.SessionImpl.getEntityPersister(SessionImpl.java:1338)
	org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:96)
	org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:186)
	org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
	org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:175)
	org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
	org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
	org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
	org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
	org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)
	br.hibernate.dao.Atributos1NivelDAO.salva(Atributos1NivelDAO.java:17)
	br.struts.action.GeraCombinacaoAction.execute(GeraCombinacaoAction.java:45)
	org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58)
	org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67)
	org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
	org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
	org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
	org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
	org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
	org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
	org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:803)


nota La traza completa de la causa de este error se encuentra en los archivos de diario de Apache Tomcat/6.0.13.

package br.modelo;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Atributos1Nivel {
	@Id
	@GeneratedValue
	private int id;
	private int nutrientes;
	private int calorias;
	private int felicidade;
	private int agua;
	private int temperatura;
	
		
	public int getNutrientes() {
		return nutrientes;
	}
	public void setNutrientes(int nutrientes) {
		this.nutrientes = nutrientes;
	}
	public int getCalorias() {
		return calorias;
	}
	public void setCalorias(int calorias) {
		this.calorias = calorias;
	}
	public int getFelicidade() {
		return felicidade;
	}
	public void setFelicidade(int felicidade) {
		this.felicidade = felicidade;
	}
	public int getAgua() {
		return agua;
	}
	public void setAgua(int agua) {
		this.agua = agua;
	}
	public int getTemperatura() {
		return temperatura;
	}
	public void setTemperatura(int temperatura) {
		this.temperatura = temperatura;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}

}