java - 500 内部服务器错误，获取请求时出现 NullPointerException

Question

我正在开发一个 Spring Boot 项目，

我尝试从 postman 发送获取请求，但收到 500 内部服务器错误。

请帮助我改进代码。

Controller :

@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:

1.问题模型:

@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);
}
}

2.选项型号:

@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 +
            '}';
}
}

存储库: 1.问题存储库

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

2.OptionRepository

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

服务:

@Service
public class sessionMcqService {

@Autowired
private QuestionRepository repository;

public List<Question> getAll(){

    return repository.findAll();
}

}

错误:

java.lang.NullPointerException: null at com.bluepi.TrainingProject.controller.sessionMcqController.getAll(sessionMcqController.java:22) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201] at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.16.jar:9.0.16] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

Answer 1

您需要在 sessionMcqController.java 上的 private sessionMcqService service; 行上方添加 @Autowired。