问题描述
1.需求我想通过获得user,然后获得user的group的信息,但是我不知道为何出现了这样神奇的异常?2.代码package com.macrotea.hb.model;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToMany;import javax.persistence.Table;@Entity@Table(name="tb_group")public class Group { private int id; private String name; private Set<User> users=new HashSet<User>(); @Id @GeneratedValue public int getId() { return id; } public String getName() { return name; } @OneToMany( mappedBy = "group", cascade = { CascadeType.ALL } ) public Set<User> getUsers() { return users; } public void setId(int id) { this.id = id; } public void setName(String name) { this.name = name; } public void setUsers(Set<User> users) { this.users = users; } @Override public String toString() { return "Group [id=" + id + ", name=" + name + ", users=" + users + "]"; } }package com.macrotea.hb.model;import java.io.Serializable;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.ManyToOne;import javax.persistence.Table;@Entity@Table(name="tb_user")public class User implements Serializable{ private int id; private String name; private Group group; @ManyToOne( cascade={CascadeType.ALL},fetch=FetchType.EAGER ) public Group getGroup() { return group; } public void setGroup(Group group) { this.group = group; } @Id @GeneratedValue public int getId() { return id; } public String getName() { return name; } public void setId(int id) { this.id = id; } public void setName(String name) { this.name = name; } @Override public String toString() { return "User [group=" + group + ", id=" + id + ", name=" + name + "]"; }} //main方法的测试 private static void test_lazy_get() { //准备 // @ManyToOne( // cascade={CascadeType.ALL},fetch=FetchType.EAGER // ) // @OneToMany( // mappedBy = "group", cascade = { CascadeType.ALL } // ) Session session=HibernateSessionFactory.getSession(); Transaction transaction=session.beginTransaction(); transaction.begin(); User user=(User)session.get(User.class, 1); System.out.println("user:"+user); System.out.println("user的group:"+user.getGroup().toString()); transaction.commit(); session.close(); }3.出错信息:Hibernate: select user0_.id as id1_1_, user0_.group_id as group3_1_1_, user0_.name as name1_1_, group1_.id as id0_0_, group1_.name as name0_0_ from tb_user user0_ left outer join tb_group group1_ on user0_.group_id=group1_.id where user0_.id=?Hibernate: select users0_.group_id as group3_1_, users0_.id as id1_, users0_.id as id1_0_, users0_.group_id as group3_1_0_, users0_.name as name1_0_ from tb_user users0_ where users0_.group_id=?Exception in thread "main" java.lang.StackOverflowErrorat java.lang.StringBuilder.append(StringBuilder.java:119)at java.lang.StringBuilder.<init>(StringBuilder.java:93)at com.macrotea.hb.model.Group.toString(Group.java:44)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.User.toString(User.java:43)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at java.util.AbstractCollection.toString(AbstractCollection.java:422)at org.hibernate.collection.PersistentSet.toString(PersistentSet.java:333)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.Group.toString(Group.java:44)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.User.toString(User.java:43)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at java.util.AbstractCollection.toString(AbstractCollection.java:422)at org.hibernate.collection.PersistentSet.toString(PersistentSet.java:333)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.Group.toString(Group.java:44)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.User.toString(User.java:43)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at java.util.AbstractCollection.toString(AbstractCollection.java:422)at org.hibernate.collection.PersistentSet.toString(PersistentSet.java:333)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.Group.toString(Group.java:44)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.User.toString(User.java:43)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at java.util.AbstractCollection.toString(AbstractCollection.java:422)at org.hibernate.collection.PersistentSet.toString(PersistentSet.java:333)at java.lang.String.valueOf(String.java:2826)at java.lang.StringBuilder.append(StringBuilder.java:115)at com.macrotea.hb.model.Group.toString(Group.java:44) (略)4.问题不知道是不是自己的配置出了什么问题?5.帖尾小生在此感谢了。临帖涕零，不知所言！
解决方案
toString方法不对，user打印了group，group里又打印user，无限循环，内存溢出