javax.ejb.EJBException：java.lang.NullPointerException

Question

我尝试使用hibernate和wildfly-10.1.0.Final

实现泛型Dao

BaseDao.java

BaseDao<T, PK extends Serializable> implements BaseDaoI<T, PK>

@Override
public T save(T t) {
    try {
        this.entityManager.persist(t);
        return t;
    } catch (PersistenceException pe) {
        return null;
    }
}

StudentDao.java

public class StudentDao extends BaseDao<Student, Long>{

public StudentDao(EntityManager entityManager) {
    super(Student.class, entityManager);
}}

StudentBean.java

 @Stateless
public class StudentBean implements StudentBeanLocal {

@PersistenceContext(name = "com.erick_SchoolManagementSystem_war_1.0-SNAPSHOTPU")
EntityManager em;
StudentDao stud = new StudentDao(em);

@Override
public Student add(Student student) {
    return stud.save(student);
}

RegisterStudent.java

@EJB
StudentBeanLocal studentbean;
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    Student student = new Student();
    student.setFirst_name(request.getParameter("first_name"));
    student.setLast_name(request.getParameter("last_name"));
    student.setUsername(request.getParameter("user_name"));
    student.setPassword(request.getParameter("password"));
    if(studentbean.add(student)!=null){
        response.sendRedirect("Login.jsp");
    }else{
        response.sendRedirect("Register.jsp");
    }

当我填写表格进行注册和提交时，我收到以下错误：

  

引起：java.lang.NullPointerException       在com.erick.schoolmanagementsystem.dao.BaseDao.save（BaseDao.java:34）