Ошибка вывода данных на страницу

package util;
 
import entity.FormObuch;
import entity.Grupa;
import entity.Kontakt;
import entity.OldSurname;
import entity.Specialnost;
import entity.Status;
import entity.Student;
import entity.TipKontakt;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.SessionFactory;
 
/**
 * Hibernate Utility class with a convenient method to get Session Factory
 * object.
 *
 * @author механик
 */
public class HibernateUtil {
 
    private static final SessionFactory sessionFactory;
    
    static {
        try {
            // Create the SessionFactory from standard (hibernate.cfg.xml) 
            // config file.
            
            AnnotationConfiguration ac = new AnnotationConfiguration();
            ac.addAnnotatedClass(Student.class);
            ac.addAnnotatedClass(Grupa.class);
            ac.addAnnotatedClass(FormObuch.class);
            ac.addAnnotatedClass(Kontakt.class);
            ac.addAnnotatedClass(OldSurname.class);
            ac.addAnnotatedClass(Specialnost.class);
            ac.addAnnotatedClass(Status.class);
            ac.addAnnotatedClass(TipKontakt.class);
            sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Log the exception. 
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }
    
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

mport java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
 
 
/**
 *
 * @author механик
 */
@Entity
public class Student implements Serializable{
 
  
        private int studentId;
  
    private String studentName;
    private String studentSurname;
    private String studentFathername;
    private Set<Kontakt> kontakts = new HashSet<>();
    private Set<Grupa> groups = new HashSet<>();
    private Set<Specialnost> specialnost = new HashSet<>();
    private Status status;
    private Set<OldSurname> oldSurn = new HashSet<>();
        
       
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
        public int getStudentId() {
        return studentId;
    }
    public void setStudentId(int studentId) {
        this.studentId = studentId;
    }
      
 
    public String getStudentName() {
        return studentName;
    }
    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }
    
 
    public String getStudentSurname() {
        return studentSurname;
    }
    public void setStudentSurname(String studentSurname) {
        this.studentSurname = studentSurname;
    }
    
 
    public String getStudentFathername() {
        return studentFathername;
    }
    public void setStudentFathername(String studentFathername) {
        this.studentFathername = studentFathername;
    }
    
 
    @ManyToOne(cascade = CascadeType.ALL)
    public Status getStatus() {
        return status;
    }
    public void setStatus(Status status) {
        this.status = status;
    }
    
    @ManyToMany
    @JoinTable(name = "student_kontakts", 
            joinColumns ={@JoinColumn(name = "studentId")}, 
inverseJoinColumns = {@JoinColumn(name="kontaktId")}
    )
    public Set<Kontakt> getKontakts() {
        return kontakts;
    }
 
    public void setKontakts(Set<Kontakt> kontakts) {
        this.kontakts = kontakts;
    }
 
    @ManyToMany
    @JoinTable(name = "student_grups", 
            joinColumns ={@JoinColumn(name = "studentId")}, 
inverseJoinColumns = {@JoinColumn(name="grupaId")}
    )
    public Set<Grupa> getGroups() {
        return groups;
    }
 
    public void setGroups(Set<Grupa> groups) {
        this.groups = groups;
    }
    
    @ManyToMany(mappedBy = "students")
    
    public Set<Specialnost> getSpecialnost() {
        return (Set<Specialnost>) specialnost;
    }
 
 
    public void setSpecialnost(Set<Specialnost> specialnost) {
        this.specialnost = specialnost;
    }
 
    /**
     * @return the oldSurn
     */
    @OneToMany(mappedBy = "student")
    public Set<OldSurname> getOldSurn() {
        return oldSurn;
    }
 
    /**
     * @param oldSurn the oldSurn to set
     */
    public void setOldSurn(Set<OldSurname> oldSurn) {
        this.oldSurn = oldSurn;
    }
 /* public void chengSurname(String newSurname){
    OldSurname oldSurname = new OldSurname(studentSurname, new Date());
    oldSurname.setStudent(this);
    Set<OldSurname> oldSurnames = new HashSet<>();
    
    oldSurnames.add(oldSurname);
    this.setOldSurn(oldSurnames);
        this.studentSurname=newSurname;
    }*/
  
}

package dao;
 
import entity.Grupa;
import java.util.List;
import entity.Student;
import java.util.Set;
/**
 *
 * @author механик
 */
public interface StudentDAO {
    
    public void addStudent (Student st );
    
    public void updStudent (Student st);
    
    public void delStudent (Student st);
    
   /* public Set<Student> findStudentByGrupa (Grupa groups);
    
    public List<Student> findStudentByGrupa (String groupsName);*/
    
    public List<Student> getStudentByName (String studentName);
    
   // public Student getStudentBySurname (String studentSurname);
}

package dao.impl;
 
import dao.StudentDAO;
import entity.Grupa;
import entity.Student;
import java.util.List;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.criterion.Restrictions;
import util.HibernateUtil;
 
/**
 *
 * @author механик
 */
public class StudentDAOImpl implements StudentDAO{
 
    @Override
    public void addStudent(Student st) {
            Session s = HibernateUtil.getSessionFactory().getCurrentSession();
        s.beginTransaction();
        s.save(st);
        s.getTransaction().commit(); 
    }
 
    @Override
    public void updStudent(Student st) {
            Session s = HibernateUtil.getSessionFactory().getCurrentSession();
        s.beginTransaction();
        s.update(st);        
        s.getTransaction().commit();
    }
 
    @Override
    public void delStudent(Student st) {
           Session s = HibernateUtil.getSessionFactory().getCurrentSession();
        s.beginTransaction();
        s.delete(st);
        s.flush();
        s.getTransaction().commit();
    }
 
 
    @Override
     public List<Student> getStudentByName (String studentName) {
         Session s = HibernateUtil.getSessionFactory().openSession();
        s.beginTransaction();
        List<Student> st = s.createQuery("from Student as st where st.studentName = ?")
                .setString(0, studentName)
                .list();
        s.getTransaction().commit();
        s.close();
        return st;
    }  
}

package beans;
 
import dao.StudentDAO;
import dao.impl.StudentDAOImpl;
import entity.Student;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
 
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author student307
 */
public class StudentBean {
 
    private List<Student> students;
 
    public StudentBean() {
        students = getStudents();
      
    }
    /**
     * @return the student
     */
    public List<Student> getStudents() {
        StudentDAO sdi = new StudentDAOImpl();
        List<Student> students = new ArrayList<Student>();
        students = sdi.getStudentByName("Иван");
        return students;
    }
 
    /**
     * @param student the student to set
     */
    public void setStudents(List<Student> students) {
        this.students = students;
    }