Spring JPA @ManytoMany StackOverflowError

Question

许多与Class和Section之间的关系如下：

 @Entity
@Table(name = "class")
public class Classz extends BaseEntity{
    private int classId;
    private String className;

    private Set<ClassSection> classHasSections;

    public Classz() {

    }

    public Classz(String className) {
        this.className = className;
        classHasSections = new HashSet<>();
    }

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getClassId() {
        return classId;
    }

    public void setClassId(int classId) {
        this.classId = classId;
    }

    public String getClassName() {
        return className;
    }

    public void setClassName(String className) {
        this.className =className;
    }

    @OneToMany(mappedBy = "classz", cascade = CascadeType.ALL, orphanRemoval = true,fetch = FetchType.EAGER)
    public Set<ClassSection>   getClassHasSections() {
        return classHasSections;
    }

    public void setClassHasSections(Set<ClassSection> classHasSections) {
        this.classHasSections = classHasSections;
    }

    @Override
    public String toString() {
        return "Classz{" +
                "className='" + className + '\'' +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Classz classz = (Classz) o;

        return classId == classz.classId;

    }

    @Override
    public int hashCode() {
        return classId;
    }
}

Section.java

@Entity(name = "section")
public class Section extends BaseEntity {
    private int sectionId;
    private String sectionName;
    private Set<ClassSection> classSections;

    public Section(){

    }

    public Section(String sectionName){
        this.sectionName = sectionName;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getSectionId() {
        return sectionId;
    }

    public void setSectionId(int sectionId) {
        this.sectionId= sectionId;
    }

    public String getSectionName() {
        return sectionName;
    }

    public void setSectionName(String sectionName) {
        this.sectionName = sectionName;
    }

    @OneToMany(mappedBy = "section")
    public Set<ClassSection> getClassSections() {
        return classSections;
    }

    public void setClassSections(Set<ClassSection> classSections) {
        this.classSections = classSections;
    }

    @Override
    public String toString() {
        return "Section{" +
                "sectionName='" + sectionName + '\'' +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Section section = (Section) o;

        return sectionId == section.sectionId;

    }

    @Override
    public int hashCode() {
        return sectionId;
    }
}

ClassSection.java

@Entity
@Table(name = "class_has_section")
public class ClassSection implements Serializable{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer classSectionId;

    private Classz classz;
    private Section section;
    private Integer capacity;

    @Id
    @ManyToOne
    @JoinColumn(name = "class_id")
    public Classz getClassz() {
        return classz;
    }

    public void setClassz(Classz classz) {
        this.classz = classz;
    }

    @Id
    @ManyToOne
    @JoinColumn(name = "section_id")
    public Section getSection() {
        return section;
    }

    public void setSection(Section section) {
        this.section= section;
    }

    @Column(name = "capacity")
    public Integer getCapacity() {
        return capacity;
    }

    public void setCapacity(Integer capacity) {
        this.capacity = capacity;
    }

    public Integer getClassSectionId() {
        return classSectionId;
    }

    public void setClassSectionId(Integer classSectionId) {
        this.classSectionId = classSectionId;
    }

    @Override
    public String toString() {
        return "ClassSection{" +
                "classSectionId=" + classSectionId +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        ClassSection that = (ClassSection) o;

        return classSectionId != null ? classSectionId.equals(that.classSectionId) : that.classSectionId == null;

    }

    @Override
    public int hashCode() {
        return classSectionId != null ? classSectionId.hashCode() : 0;
    }
}

在Springboot应用程序中，我运行以下命令。考虑这样的情况，其中一个记录已经插入到db中，用于类和section以及classSection。

由Springboot应用程序运行程序调用的方法

@Transactional
    public void runTest1(){

        Classz classz = new Classz("6");

        Section section = new Section("F");

        ClassSection classSection = new ClassSection();
        classSection.setClassz(classz);
        classSection.setSection(section);
        classSection.setCapacity(1);

        classz.getClassHasSections().add(classSection);
        sectionRepository.save(section);
        classRepository.save(classz);


        // test


        // update
        //bookA.getBookPublishers().remove(bookPublisher);
        //  Classz classz1 = new Classz();
        //classz1.setClassId(4);
        Classz bok=classRepository.findOne(1); // StackOverflowError
       // Classz bok=classRepository.findOne(classz1.getClassId()); //Worked 
        // test
        System.out.println("Size ===="+bok.getClassHasSections().size());

    }

这里考虑1已经插入了ID： 发生以下错误：

java.lang.StackOverflowError: null
    at sun.nio.cs.StreamEncoder.write(StreamEncoder.java:117) ~[na:1.8.0_45]
    at java.io.OutputStreamWriter.write(OutputStreamWriter.java:207) ~[na:1.8.0_45]
    at java.io.BufferedWriter.flushBuffer(BufferedWriter.java:129) ~[na:1.8.0_45]
    at java.io.PrintStream.write(PrintStream.java:526) ~[na:1.8.0_45]
    at java.io.PrintStream.print(PrintStream.java:669) ~[na:1.8.0_45]

任何人都可以帮忙吗？或有类似的问题。我对这个问题提出了一些问题。建议是toString（）和hasCode（）但到目前为止没有运气