当我在 Spring 中从我的服务层返回实体列表时，我不断收到来自 Tomcat 的错误 500。如果我只是在内存中动态创建实体，我不会收到错误并且它们返回正常，所以这与事务有关。
我的控制器中有以下方法...
@RequestMapping(value = "{examid}", method = RequestMethod.GET)
@ResponseBody
public List<Exam> getExam(@PathVariable String examid, Model model) {
return examService.getAllExams();
}
调用此方法时，tomcat 显示错误 500 并且根本没有堆栈跟踪。我什至将它包装在一个 try catch 中，并且该堆栈跟踪中没有任何内容。
这个服务只是调用一个 dao...
@Service("examService")
public class ExamServiceImpl implements ExamService{
@Autowired
private ExamDao examDao;
@Override
@Transactional(readOnly = true)
public List<Exam> getAllExams() {
return examDao.getAllExams();
}
而这个 dao 只是返回一个简单的 HQL 脚本......
@Repository("examDao")
public class ExamDaoImpl implements ExamDao {
@Autowired
private SessionFactory sessionFactory;
@Override
public List<Exam> getAllExams() {
return sessionFactory.getCurrentSession().createQuery("from Exam")
.list();
}
最初，我认为这与延迟加载的实体有关，如您所见，我的实体如下所示，它们非常简单
@Entity
@Table(name = "exams")
public class Exam implements Serializable {
private static final long serialVersionUID = -5109075534794721930L;
@Id
@GeneratedValue(generator="system-uuid")
@GenericGenerator(name="system-uuid", strategy = "uuid")
@Column(name = "examid", unique = true)
private String examId;
@OneToMany(mappedBy = "exam")
private Set<Question> questions;
public String getExamId() {
return examId;
}
public void setExamId(String examId) {
this.examId = examId;
}
/**
* @return the questions
*/
@JsonManagedReference
public Set<Question> getQuestions() {
return questions;
}
/**
* @param questions the questions to set
*/
public void setQuestions(Set<Question> questions) {
this.questions = questions;
}
}
问题实体
@Entity
@Table(name = "questions")
public class Question implements Serializable {
private static final long serialVersionUID = 8804841647267857850L;
private String questionId;
private Exam exam;
private Set<Answer> answers;
/**
* @return the answer
*/
@JsonManagedReference
@OneToMany(mappedBy = "question")
public Set<Answer> getAnswers() {
return answers;
}
/**
* @param answer
* the answer to set
*/
public void setAnswers(Set<Answer> answers) {
this.answers = answers;
}
/**
* @return the exam
*/
@JsonBackReference
@ManyToOne
@JoinColumn(name = "examid", nullable = false)
public Exam getExam() {
return exam;
}
/**
* @param exam
* the exam to set
*/
public void setExam(Exam exam) {
this.exam = exam;
}
/**
* @return the questionId
*/
@Id
@GeneratedValue(generator = "system-uuid")
@GenericGenerator(name = "system-uuid", strategy = "uuid")
@Column(name = "questionid", unique = true)
public String getQuestionId() {
return questionId;
}
/**
* @param questionId
* the questionId to set
*/
public void setQuestionId(final String questionId) {
this.questionId = questionId;
}
}
回答实体
@Entity
@Table(name = "answers")
public class Answer implements Serializable {
private static final long serialVersionUID = -3922870865886851018L;
@Id
@GeneratedValue(generator="system-uuid")
@GenericGenerator(name="system-uuid", strategy = "uuid")
@Column(name = "answerid", unique = true)
private String answerId;
@ManyToOne()
@JoinColumn(name = "questionid", nullable = false)
private Question question;
/**
* @return the question
*/
@JsonBackReference
public Question getQuestion() {
return question;
}
/**
* @param question the question to set
*/
public void setQuestion(Question question) {
this.question = question;
}
/**
* @return the answerId
*/
public String getAnswerId() {
return answerId;
}
/**
* @param answerId the answerId to set
*/
public void setAnswerId(final String answerId) {
this.answerId = answerId;
}
}
我正在使用 Jackson 2.2.0 - 现在下面的代码工作正常，所以这肯定是连接的一些问题（最初是延迟加载但为了调试而删除的）。只需从控制器返回以下代码就可以了...
Exam exam = new Exam();
Question presidentQuestion = new Question();
presidentQuestion.setExam(exam);
Question skyQuestion = new Question();
skyQuestion.setExam(exam);
Set<Question> questions = new HashSet<>();
questions.add(skyQuestion);
questions.add(presidentQuestion);
exam.setQuestions(questions);
Answer answer = new Answer();
answer.setQuestion(skyQuestion);
Answer answer1 = new Answer();
answer1.setQuestion(skyQuestion);
Answer answer2 = new Answer();
answer2.setQuestion(presidentQuestion);
Set<Answer> answers1 = new HashSet<>();
answers1.add(answer2);
Set<Answer> answers = new HashSet<>();
answers.add(answer);
answers.add(answer1);
presidentQuestion.setAnswers(answers1);
skyQuestion.setAnswers(answers);
return Arrays.asList(exam);
Tomcat 日志中没有任何内容 - 如何强制执行某种堆栈跟踪？Hibernate 版本 = 4.1.10.Final，Spring 版本 3.1.4。