500内部服务器错误，获取请求时为NullPointerException

Question

我在做一个春靴项目，

我正试图从邮递员发送get请求，但我得到500个内部服务器错误。

控制器：

@RestController
@RequestMapping("/admin")
@CrossOrigin(origins = "http://localhost:4200")
public class sessionMcqController {

@Autowired
private sessionMcqService service;

@GetMapping("/viewmcq")
public List<Question> getAll(){
    return service.getAll();
}

}

型号：

@Entity
@Table(name = "mcq_question")
public class Question {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@JoinColumn (name = "questionId")
private Long questionId;

@Column(nullable = false)
private String question;

@OneToOne(fetch = FetchType.LAZY, targetEntity = Option.class)
@JoinTable( name = "mcq_answer", joinColumns = @JoinColumn ( name = "question_id"), inverseJoinColumns = @JoinColumn( name = "option_id"))
private List <Option> options;

@OneToMany(mappedBy = "questionId", cascade = CascadeType.ALL)
private Set<Option> option;

public Question() { }

public Long getMcqId() {
    return questionId;
}

public void setMcqId(Long mcqId) {
    this.questionId = mcqId;
}

public String getQuestion() {
    return question;
}

public void setQuestion(String question) {
    this.question = question;
}

@Override
public String toString() {
    return "McqModel{" +
            "mcqId=" + questionId +
            ", question='" + question + '\'' +
            '}';
}

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Question question1 = (Question) o;
    return questionId.equals(question1.questionId) &&
            question.equals(question1.question) &&
            options.equals(question1.options) &&
            option.equals(question1.option);
}

@Override
public int hashCode() {
    return Objects.hash(questionId, question, options, option);
}
}

@Entity
@Table(name = "mcq_Options")
public class Option {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "option_id")
private int optionId;

private String option;

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn
private Question questionId;

public Option() { }

public Option(String option, Question questionId) {
    this.option = option;
}

public int getOptionId() {
    return optionId;
}

public void setOptionId(int optionId) {
    this.optionId = optionId;
}

public String getOption() {
    return option;
}

public void setOption(String option) {
    this.option = option;
}

public Question getQuestionId() {
    return questionId;
}

public void setQuestionId(Question questionId) {
    this.questionId = questionId;
}

@Override
public String toString() {
    return "Option{" +
            "optionId=" + optionId +
            ", option='" + option + '\'' +
            ", questionId=" + questionId +
            '}';
}
}

@Repository
public interface QuestionRepository extends JpaRepository<Question, Long> {
}

@Repository
public interface OptionRepository extends JpaRepository<Option, Integer> {
}

@Service
public class sessionMcqService {

@Autowired
private QuestionRepository repository;

public List<Question> getAll(){

    return repository.findAll();
}

}

Answer 1

您需要在专用sessionMcqService服务的上方添加@AutoWired；SessionMcQController.java上的行。