保存spring实体时的java.lang.NullPonterException

Question

我尝试读取ExcelFiles并将数据保存在postgres数据库中。在某些文件中,我会得到以下错误消息：

null

@Entity
public class SemesterLecture implements Serializable {
    @Id
    @ManyToOne
    @JsonIgnore
    @JoinColumn
    private Semester semester;

    @Id
    @ManyToOne
    @JoinColumn
    private Lecture lecture;

    private String grade;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
    private List<LectureDateTime> lectureDateTimes;

    public SemesterLecture(Lecture lecture, String grade) {
        this.lecture = lecture;
        this.grade = grade;
    }

    public SemesterLecture() {
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof SemesterLecture)) return false;
        SemesterLecture that = (SemesterLecture) o;
        return Objects.equals(semester.getTitle(), that.semester.getTitle()) &&
                Objects.equals(lecture.getTitle(), that.lecture.getTitle());
    }

@Override
    public int hashCode() {
        return Objects.hash(semester.getTitle(), lecture.getTitle(), grade);
    }

@EventListener(ApplicationReadyEvent.class)
    @Transactional
    public void readExcelFileFolder() throws IOException, InvalidFormatException, NotFoundException {
        LOG.info("Load Excel Files from folder...");
        FileFilter filter = new ExcelFileFilter ();
        Resource[] resourceFiles = resourcePatternResolver.getResources("classpath:excel-files/*.xls");
        for (Resource resource : resourceFiles) {
            readExcelFile(resource.getInputStream(), resource.getFilename());
        }
    }

    public void readExcelFile(InputStream inputStream, String fileName) throws IOException, InvalidFormatException, NotFoundException {
        Workbook workbook = WorkbookFactory.create(inputStream);
        DataFormatter dataFormatter = new DataFormatter();
        LOG.info("Read Excel File: " + fileName.substring(0, fileName.lastIndexOf('.')));

        Course existingCourse = courseRepository.findByCourseNumber(fileName.replace(" ", "").substring(0, fileName.lastIndexOf('.')));
        if(existingCourse == null){
            return;
        }
        LOG.info("Found course with title " + existingCourse.getCourseTitle());

        if(existingCourse.getSemesters().size() < 1){
            for(int i = 1; i < 8; i++){
                Semester semester = new Semester();
                semester.setTitle("Semester " + i);
                semester.setSemesterLectures(new ArrayList<SemesterLecture>());
                semester.setSemesterNumber(i);
                existingCourse.getSemesters().add(semesterRepository.save(semester));
            }
            LOG.info("Added " + existingCourse.getSemesters().size() + " Semesters");
        }

        for(int y = 0; y < 5; y++){
            Sheet sheet = workbook.getSheetAt(y);
            for (Row row: sheet) {
                String title = dataFormatter.formatCellValue(row.getCell(0));
                String modulNumber = dataFormatter.formatCellValue(row.getCell(1)).replace(" ", "");
                String language = dataFormatter.formatCellValue(row.getCell(2));
                int semesterNumber = 1;
                try{
                    semesterNumber = Integer.parseInt(dataFormatter.formatCellValue(row.getCell(3)).replace(".", ""));
                }catch (Exception e){}
                if(title instanceof String && modulNumber instanceof String && !title.isEmpty() && !modulNumber.isEmpty() && !title.startsWith("Module")){
                    try{
                        if(lectureRepository.existsByModulNumber(modulNumber.replace(" ", ""))){
                            Lecture lecture = lectureRepository.findByModulNumber(modulNumber.replace(" ", ""));
                            SemesterLecture sm = new SemesterLecture(lecture, "0");
                            sm.setSemester(existingCourse.getSemesters().get(semesterNumber-1));
                            sm.setLecture(lecture);
                            sm.setGrade("0");
                            existingCourse.getSemesters().get(semesterNumber-1).getSemesterLectures().add(sm);
                            LOG.info(sm.getLecture().getTitle() + sm.getSemester().getTitle());
                        }
                    } catch (NumberFormatException e) {
                        throw new NotFoundException("Lecture does not exist");
                    }
                }
            }
        }

        for(Semester semester : existingCourse.getSemesters()){
            semesterRepository.save(semester);
        }
        courseRepository.save(existingCourse);
        LOG.info("Saved all lectures from course " + existingCourse.getCourseTitle());
    }

在大多数已爬网的数据中，什么都没有发生。当我尝试保存semster对象时会出现错误。Excel文件的结构如下：标题、模块号、语言、学期号

Answer 1

在进行堆栈跟踪时,我认为您有两个问题：

• 第一个被第二个隐藏的是，您正在尝试保存一个SemesterClacture实例，该实例与html" target="_blank">数据库中已存在的一个实例具有相同的主id（即，对两个SemesterClacture具有相同的值），因此可以在堆栈跟踪中看到NonUniqueObjectException
• 第二个是，spring在尝试打印NonUniqueObjectException的消息时，通过调用SemesterLeaction类的哈希方法来结束，该实例的字段SEMERT或LEACTION设置为null，因此NullPointerException很好。

我的建议：

首先，删除或注释SemesterPracture类的哈希方法。默认的一个已经足够开始了，它将允许您看到您的原始异常。我的猜测是，在你的学期或你的讲座课hash或equals方法中有一个bug，导致hibernate将两个实体误认为同一个实体。