@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Contrat implements Serializable{

        @Id @GeneratedValue
        private Long id;
        private Date dateDebut ;
        private Date dateFin ;
        @ManyToOne
        @JoinColumn(name = "Id_Project")
        @JsonBackReference(value="projet-contrat")
        private Project project;

        @ManyToOne
        @JoinColumn(name = "Id_AppUser")
        @JsonBackReference(value="appuser-contrat")
        private AppUser appUser;
}

public interface ContratRepo extends JpaRepository<Contrat,Long> {

    @Query("select from Contrat c where c.appUser = :userApp")
    public Page<Contrat> chercherContrat(@Param("userApp") AppUser userApp
   , Pageable pageable);

   }

{id: 1, dateDebut: 1526083200000, dateFin: 1526083200000}