JSF转换器中的NullPointerException

我有一个表用户和专门的数据库

用户：

CREATE  TABLE IF NOT EXISTS `ePrzychodnia`.`users` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `firstName` VARCHAR(45) NOT NULL ,
  `lastName` VARCHAR(45) NOT NULL ,
  `specialization_id` INT NULL ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `personalId_UNIQUE` (`personalId` ASC) ,
  INDEX `fk_users_specializations1_idx` (`specialization_id` ASC) ,
  CONSTRAINT `fk_users_specializations1`
    FOREIGN KEY (`specialization_id` )
    REFERENCES `ePrzychodnia`.`specializations` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

public class User implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    private Integer id;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "firstName")
    private String firstName;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "lastName")
    private String lastName;
    @Basic(optional = false)
    @JoinColumn(name = "specialization_id", referencedColumnName = "id")
    @ManyToOne
    private Specialization specializationId;

专业：

CREATE  TABLE IF NOT EXISTS `ePrzychodnia`.`specializations` (
  `id` INT NOT NULL ,
  `name` VARCHAR(45) NOT NULL ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `name_UNIQUE` (`name` ASC) )
ENGINE = InnoDB;

实体类：

用户：

CREATE  TABLE IF NOT EXISTS `ePrzychodnia`.`users` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `firstName` VARCHAR(45) NOT NULL ,
  `lastName` VARCHAR(45) NOT NULL ,
  `specialization_id` INT NULL ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `personalId_UNIQUE` (`personalId` ASC) ,
  INDEX `fk_users_specializations1_idx` (`specialization_id` ASC) ,
  CONSTRAINT `fk_users_specializations1`
    FOREIGN KEY (`specialization_id` )
    REFERENCES `ePrzychodnia`.`specializations` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

public class User implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    private Integer id;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "firstName")
    private String firstName;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "lastName")
    private String lastName;
    @Basic(optional = false)
    @JoinColumn(name = "specialization_id", referencedColumnName = "id")
    @ManyToOne
    private Specialization specializationId;

专业化：

public class Specialization implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @NotNull
    @Column(name = "id")
    private Integer id;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "name")
    private String name;
    @OneToMany(mappedBy = "specializationId")
    private Collection<User> userCollection;

但这是行不通的；/我有一个错误：

WARNING: StandardWrapperValve[Faces Servlet]: PWC1406: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
    at pl.Project.dao.SpecializationDao.find(SpecializationDao.java:36)
    at pl.Project.converter.SpecializationConverter.getAsObject(SpecializationConverter.java:29)

专业化DAO：

@Stateless
public class SpecializationDao implements SpecializationDaoLocal {

    @PersistenceContext
    private EntityManager em;
    private Specialization specialization;

    public SpecializationDao() {
    }

    public SpecializationDao(Specialization specialization) {
        this.specialization = specialization;
    }

    @Override
    public Specialization find(int specializationId) {
        return em.find(Specialization.class, specializationId);
    }

    @Override
    public List<Specialization> findAllSpecialization() {
        Query q = em.createNamedQuery("Specialization.findAll");
        List<Specialization> specializations = q.getResultList();
        return specializations;
    }
}

@无状态
公共类SpecializationDao实现SpecializationDaoLocal{
@持久上下文
私人实体管理者；
私人专业化；
公共专业化{
}
公共专业化DAO（专业化）{
专业化=专业化；
}
@凌驾
公共专门化查找（int specializationId）{
返回em.find（Specialization.class，specializationId）；
}
@凌驾
公共列表findAllSpecialization（）{
Query q=em.createNamedQuery（“Specialization.findAll”）；
列表专门化=q.getResultList（）；
返回专业化；
}
}

读取堆栈跟踪。

specializationDao.find

方法中有一个

null

变量。哪一个可能是？这取决于你和调试器找到它。顺便说一句，添加数据库表、JPA实体和转换器的所有信息与问题无关，这也不是JSF的问题。@Orange91您发布了很多东西，但错过了

SpecializationDao

！！！可能的副本。顺便说一句，这个问题是因为您手动创建EJB而不是注入它，所以不会创建

EntityManager em

，因此

为null

，并为您提供NPE。@Luiggi:无法在

@FacesConverter

中使用

@EJB

，实际上是一个真正的JSF问题。OP只是试图以错误的方式解决它，因此不再是JSF的问题：）@Luiggi：是的，现在他实际上在stacktrace的第1行后面发布了代码，这变得更加清楚了。Orange：现在是学习如何解释stacktraces的时候了，这实际上是基本Java，与JSF无关。