spring mvc报错，数据库查询无限死循环

进行查询的陷入了无限死循环，原因是问题类中包含了回答，回答类中包含了问题，进入了无限死循环

解决方法：在回答类中的问题类属性上加注解：@JsonBackReference

问题中有回答的set集合，回答中有问题类：

问题类：

package com.wazn.learn.entity.teachclass;

import java.util.Date;

import java.util.HashSet;

import java.util.List;

import java.util.Set;

import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.OneToMany;

import javax.persistence.Table;

import com.wazn.learn.entity.sys.User;

/**

 *

 * 提问表

 *

 */

@Entity

@Table(name="teach_questions")

public class Questions {

    private Integer id;//id

    private User userid;//学生id

    private TeachClass cid;//课程id

    private String question;//提问

    private Date twtime;//提问时间

    private String title;

    private Set<Answer> answer;

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    @Column(nullable=false)

    public String getQuestion() {

        return question;

    }

    public void setQuestion(String question) {

        this.question = question;

    }

    @ManyToOne

    @JoinColumn(name="c_id",nullable=false,insertable=true)

    public TeachClass getCid() {

        return cid;

    }

    public void setCid(TeachClass cid) {

        this.cid = cid;

    }

    @ManyToOne

    @JoinColumn(name="user_id",nullable=false,insertable=true)

    public User getUserid() {

        return userid;

    }

    public void setUserid(User userid) {

        this.userid = userid;

    }

    public Date getTwtime() {

        return twtime;

    }

    public void setTwtime(Date twtime) {

        this.twtime = twtime;

    }

 @OneToMany(cascade = { CascadeType.REFRESH, CascadeType.PERSIST,CascadeType.MERGE, CascadeType.REMOVE },mappedBy ="question")

    public Set<Answer> getAnswer() {

        return answer;

    }

    public void setAnswer(Set<Answer> answer) {

        this.answer = answer;

    }

    public String getTitle() {

        return title;

    }

    public void setTitle(String title) {

        this.title = title;

    }

}

回答类：

package com.wazn.learn.entity.teachclass;

import java.util.Date;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonBackReference;

import com.wazn.learn.entity.sys.User;

@Entity

@Table(name="teach_answer")

public class Answer {

    private Integer id;

    private String content;

    private Date hftime;

    private User userid;//教师id

    private Questions question;

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    @Column(nullable=false)

    public String getContent() {

        return content;

    }

    public void setContent(String content) {

        this.content = content;

    }

    public Date getHftime() {

        return hftime;

    }

    public void setHftime(Date hftime) {

        this.hftime = hftime;

    }

    @ManyToOne

    @JoinColumn(name="u_id",nullable=false,insertable=true)

    public User getUserid() {

        return userid;

    }

    public void setUserid(User userid) {

        this.userid = userid;

    }

    @ManyToOne

    @JoinColumn(name="q_id",nullable=false,insertable=true)

    @JsonBackReference

    public Questions getQuestion() {

        return question;

    }

    @JsonBackReference

    public void setQuestion(Questions question) {

        this.question = question;

    }

    @Override

    public String toString() {

        return "Answer [id=" + id + ", content=" + content + ", hftime=" + hftime + ", userid=" + userid + ", question="

                + question + "]";

    }

}