salut,
j'ai l'erreur suivante à l'execution de mon programme :
voici le stack de l'erreur

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Exception in thread "main" javax.persistence.PersistenceException: No Persistence provider for EntityManager named jpa: Provider named oracle.toplink.essentials.PersistenceProvider threw unexpected exception at create EntityManagerFactory: 
oracle.toplink.essentials.exceptions.PersistenceUnitLoadingException
Local Exception Stack: 
Exception [TOPLINK-30005] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.PersistenceUnitLoadingException
Exception Description: An exception was thrown while searching for persistence archives with ClassLoader: sun.misc.Launcher$AppClassLoader@11b86e7
Internal Exception: javax.persistence.PersistenceException: Exception [TOPLINK-28018] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.EntityManagerSetupException
Exception Description: predeploy for PersistenceUnit [jpa] failed.
Internal Exception: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.GenericArrayTypeImpl cannot be cast to java.lang.Class
        at oracle.toplink.essentials.exceptions.PersistenceUnitLoadingException.exceptionSearchingForPersistenceResources(PersistenceUnitLoadingException.java:143)
        at oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider.createEntityManagerFactory(EntityManagerFactoryProvider.java:169)
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:110)
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83)
        at DAO.Dao.init(Dao.java:34)
        at Main.Lancement.main(Lancement.java:29)
Caused by: javax.persistence.PersistenceException: Exception [TOPLINK-28018] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.EntityManagerSetupException
Exception Description: predeploy for PersistenceUnit [jpa] failed.
Internal Exception: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.GenericArrayTypeImpl cannot be cast to java.lang.Class
        at oracle.toplink.essentials.internal.ejb.cmp3.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:643)
        at oracle.toplink.essentials.internal.ejb.cmp3.JavaSECMPInitializer.callPredeploy(JavaSECMPInitializer.java:171)
        at oracle.toplink.essentials.internal.ejb.cmp3.JavaSECMPInitializer.initPersistenceUnits(JavaSECMPInitializer.java:239)
        at oracle.toplink.essentials.internal.ejb.cmp3.JavaSECMPInitializer.initialize(JavaSECMPInitializer.java:255)
        at oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider.createEntityManagerFactory(EntityManagerFactoryProvider.java:155)
        ... 4 more
Caused by: Exception [TOPLINK-28018] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.EntityManagerSetupException
Exception Description: predeploy for PersistenceUnit [jpa] failed.
Internal Exception: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.GenericArrayTypeImpl cannot be cast to java.lang.Class
        at oracle.toplink.essentials.exceptions.EntityManagerSetupException.predeployFailed(EntityManagerSetupException.java:228)
        ... 9 more
Caused by: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.GenericArrayTypeImpl cannot be cast to java.lang.Class
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.MetadataHelper.getReturnTypeFromGeneric(MetadataHelper.java:603)
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.accessors.objects.MetadataAccessibleObject.getReferenceClassFromGeneric(MetadataAccessibleObject.java:141)
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.accessors.CollectionAccessor.getReferenceClass(CollectionAccessor.java:175)
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.accessors.RelationshipAccessor.processRelationship(RelationshipAccessor.java:287)
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.MetadataProject.processRelationshipDescriptors(MetadataProject.java:579)
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.MetadataProject.process(MetadataProject.java:512)
        at oracle.toplink.essentials.internal.ejb.cmp3.metadata.MetadataProcessor.processAnnotations(MetadataProcessor.java:246)
        at oracle.toplink.essentials.ejb.cmp3.persistence.PersistenceUnitProcessor.processORMetadata(PersistenceUnitProcessor.java:370)
        at oracle.toplink.essentials.internal.ejb.cmp3.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:607)
        ... 8 more


 The following providers:
oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider
Returned null to createEntityManagerFactory.

        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:154)
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83)
        at DAO.Dao.init(Dao.java:34)
        at Main.Lancement.main(Lancement.java:29)
Java Result: 1
BUILD SUCCESSFUL (total time: 18 seconds)
le fichier persistence.xml :

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<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
  <persistence-unit name="jpa" transaction-type="RESOURCE_LOCAL">
    <provider>oracle.toplink.essentials.PersistenceProvider</provider>
    <class>Metier.Enseignant.Enseignant</class>
    <class>Metier.Etudes.Discipline</class>
    <class>Metier.Etudes.Domaine</class>
    <class>Metier.Etudes.Module</class>
    <class>Metier.Etudes.UE</class>
    <class>Metier.Etudiant.Etats.AbstractEtatEtudiant</class>
    <class>Metier.Etudiant.Etats.EtatAttente</class>
    <class>Metier.Etudiant.Etats.EtatRattache</class>
    <class>Metier.Etudiant.Etats.EtatRecale</class>
    <class>Metier.Etudiant.Etats.EtatTermine</class>
    <class>Metier.Etudiant.Etudiant</class>
    <class>Metier.Notes.Note</class>
    <class>Metier.Notes.ReleveNotes</class>
    <class>Metier.Promotion.ASemestre</class>
    <class>Metier.Promotion.Annee</class>
    <class>Metier.Promotion.Etats.AbstractEtatPromotion</class>
    <class>Metier.Promotion.Etats.EtatEnCours_Promo</class>
    <class>Metier.Promotion.Etats.EtatEnCreation_Promo</class>
    <class>Metier.Promotion.Etats.EtatTerminee_Promo</class>
    <class>Metier.Promotion.Etats.EtatValide_Promo</class>
    <class>Metier.Promotion.EtatsAnnee.AbstractEtatAnnee</class>
    <class>Metier.Promotion.EtatsAnnee.EtatEnAttente</class>
    <class>Metier.Promotion.EtatsAnnee.EtatEnCours</class>
    <class>Metier.Promotion.EtatsAnnee.EtatEnRattrapage</class>
    <class>Metier.Promotion.EtatsAnnee.EtatTerminee</class>
    <class>Metier.Promotion.EtatsSemestre.AbstractEtatSemestre</class>
    <class>Metier.Promotion.EtatsSemestre.EtatEnAttente_Semestre</class>
    <class>Metier.Promotion.EtatsSemestre.EtatEnCours_Semestre</class>
    <class>Metier.Promotion.EtatsSemestre.EtatTerminee_Semestre</class>
    <class>Metier.Promotion.EtatsSemestre.EtatValidee_Semestre</class>
    <class>Metier.Promotion.Promotion</class>
    <class>Metier.Promotion.Semestre</class>
    <class>Metier.Etudiant.Cursus</class>
    <properties>
      <property name="toplink.jdbc.user" value="bassim"/>
      <property name="toplink.jdbc.password" value=" "/>
      <property name="toplink.jdbc.url" value="jdbc:derby:C:\Mes Documents\NetBeans Projets\Bases de données\JStudentDB"/>
      <property name="toplink.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver"/>
      <property name="toplink.ddl-generation" value="drop-and-create-tables"/>
    </properties>
  </persistence-unit>
</persistence>
en cherchant sur google j'ai trouvé les discussions suivantes:
discussion 1
discussion 2

mais étant très moyen en anglais, j'ai du mal à comprendre les discussions