Hibernate JPA:java.lang.StackOverflower关于在实体类中添加toString方法的错误
在我在实体类中添加了Hibernate JPA:java.lang.StackOverflower关于在实体类中添加toString方法的错误,hibernate,stack-overflow,jpql,tostring,jpa-2.1,Hibernate,Stack Overflow,Jpql,Tostring,Jpa 2.1,在我在实体类中添加了toSting()之前,一切都很顺利 之后,我开始在运行时出现以下错误: Exception in thread "main" java.lang.StackOverflowError at java.lang.AbstractStringBuilder.append(Unknown Source) at java.lang.StringBuilder.append(Unknown Source) at java.lang.StringBuilder.
toSting()
之前,一切都很顺利
之后,我开始在运行时出现以下错误:
Exception in thread "main" java.lang.StackOverflowError
at java.lang.AbstractStringBuilder.append(Unknown Source)
at java.lang.StringBuilder.append(Unknown Source)
at java.lang.StringBuilder.<init>(Unknown Source)
at entity.Guide.toString(Guide.java:51)
at java.lang.String.valueOf(Unknown Source)
at java.lang.StringBuilder.append(Unknown Source)
at entity.Student.toString(Student.java:45)
...
根据增加的学生班级进行更新
根据堆栈跟踪,您的问题与Student.toString()
有关,下面是发生的情况:
在Teacher.toString()
中,通过将Student
成员放置在String
连接语句中,隐式调用Student.toString()
。在Student.toString()
中,代码通过在String
连接语句中包含teacher
成员来执行类似的操作
这意味着调用Teacher.toString()
或Student.toString()
将导致一个永无止境的循环,其中:Teacher.toString()
隐式调用Student.toString()
,后者又隐式调用Teacher.toString()
,后者又调用Student.toString()
,这反过来又叫
2.toString()
实现在一个永无止境的循环中不断地来回调用,这最终会溢出堆栈并导致java.lang.StackOverflowerError
要更正此问题,应删除对实体的
.toString()
方法的隐式引用。作为替代,您可以让Teacher.toString()
只需输出Student
集合的length()
,并可能包括Student
姓名列表。在Student.toString()
中,只需包含Teacher.name
成员。实体类教师有toString()
问题:
@Entity
public class Teacher {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private String name;
@OneToMany(mappedBy="teacher", cascade={CascadeType.PERSIST})
private Set<Student> students = new HashSet<Student>();
public Teacher() {}
public Teacher(String name) {
this.name = name;
}
public Set<Student> getStudents() {
return students;
}
public void addStudent(Student student) {
students.add(student);
student.setTeacher(this);
}
@Override
public String toString() {
return "Teacher[id=" + id + ", name=" + name
+ "]";
}
}
@实体
公共班主任{
@身份证
@GeneratedValue(策略=GenerationType.AUTO)
私人长id;
私有字符串名称;
@OneToMany(mappedBy=“teacher”,cascade={CascadeType.PERSIST})
private Set students=new HashSet();
公共教师(){}
公共教师(字符串名称){
this.name=名称;
}
公共集getStudents(){
留学生;
}
公立学校学生(学生){
学生。添加(学生);
学生。塞塔彻(本);
}
@凌驾
公共字符串toString(){
返回“教师[id=“+id+”,name=“+name
+ "]";
}
}
必须从toString()方法中排除冗余参数
- 在Java中与
@ToString.Exclude一起使用
- 在Kotlin中使用带
@ExcludeToString的
GL编辑了文章,在底部添加了
Student
实体的代码。刚刚将Guide
实体中的toString
方法更新到此public String toString(){return“Guide[id=“+id+”,staffId=“+staffId+”,name=“+name+”,salary=“+salary+”,students.size()=“+students.size()+”);}
。它解决了这个问题。谢谢。@skip-我已经根据您添加的学生
课程更新了我的答案。我最初的猜测是正确的,我的回答应该能帮助你纠正这个问题。
public class SnafuClient {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("snafu");
EntityManager em = emf.createEntityManager();
EntityTransaction txn = em.getTransaction();
try {
txn.begin();
Query query = em.createQuery("select teacher from Teacher teacher");
List<Teacher> teachers = query.getResultList();
for (Teacher teacher: teachers) {
System.out.println(teacher);
}
txn.commit();
} catch(Exception e) {
if(txn != null) { txn.rollback(); }
e.printStackTrace();
} finally {
if(em != null) { em.close(); }
}
}
}
@Entity
public class Student {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private String name;
@ManyToOne(cascade={CascadeType.PERSIST, CascadeType.REMOVE})
@JoinColumn(name="teacher_id")
private Teacher teacher;
public Student() {}
public Student(String name, Teacher teacher) {
this.name = name;
this.teacher = teacher;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public String toString() {
return "Student [id=" + id +
+ ", name=" + name + ", teacher=" + teacher + "]";
}
}
@Entity
public class Teacher {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private String name;
@OneToMany(mappedBy="teacher", cascade={CascadeType.PERSIST})
private Set<Student> students = new HashSet<Student>();
public Teacher() {}
public Teacher(String name) {
this.name = name;
}
public Set<Student> getStudents() {
return students;
}
public void addStudent(Student student) {
students.add(student);
student.setTeacher(this);
}
@Override
public String toString() {
return "Teacher[id=" + id + ", name=" + name
+ "]";
}
}