使用Hibernate生成的Java Bean中的Java-ToString（）導致StackOverflowError

Question

我是這個論壇的新手，所以我希望我沒做錯任何事情。我一個月前開始學習Java，但是我有一個小問題。 我有2個實體，我想打印帶有其軌道的CD，但是我有這個異常：線程“ main”中的異常java.lang.StackOverflowError

我不知道如何解決此問題。我發布了代碼和實體：

TbTrack

package it.tgi.cd.entities2;

// default package
// Generated 11-mag-2015 16.29.34 by Hibernate Tools 4.0.0

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

/**
 * TbTrack generated by hbm2java
 */
@Entity
@Table(name = "tb_track", catalog = "db_cd_store")
public class TbTrack implements java.io.Serializable {

    private Integer idTrack;
    private TbCd tbCd;
    private String title;

    public TbTrack() {
    }

    public TbTrack(TbCd tbCd, String title) {
        this.tbCd = tbCd;
        this.title = title;
    }

    @Override
    public String toString() {
        return "idTrack=" + idTrack + ", tbCd=" + tbCd + ", title=" + title;
    }

    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "id_track", unique = true, nullable = false)
    public Integer getIdTrack() {
        return this.idTrack;
    }

    public void setIdTrack(Integer idTrack) {
        this.idTrack = idTrack;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id_cd", nullable = false)
    public TbCd getTbCd() {
        return this.tbCd;
    }

    public void setTbCd(TbCd tbCd) {
        this.tbCd = tbCd;
    }

    @Column(name = "title", nullable = false, length = 45)
    public String getTitle() {
        return this.title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

}

TBCD

package it.tgi.cd.entities2;

// default package
// Generated 11-mag-2015 16.29.34 by Hibernate Tools 4.0.0

import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

/**
 * TbCd generated by hbm2java
 */
@Entity
@Table(name = "tb_cd", catalog = "db_cd_store")
public class TbCd implements java.io.Serializable {

    private int idCd;
    private String title;
    private Set<TbTrack> tbTracks = new HashSet<TbTrack>(0);

    public TbCd() {
    }

    public TbCd(int idCd, String title) {
        this.idCd = idCd;
        this.title = title;
    }

    @Override
    public String toString() {
        return "idCd=" + idCd + ", title=" + title + ", track= " + tbTracks;
    }

    public TbCd(int idCd, String title, Set<TbTrack> tbTracks) {
        this.idCd = idCd;
        this.title = title;
        this.tbTracks = tbTracks;
    }

    @Id
    @Column(name = "id_cd", unique = true, nullable = false)
    public int getIdCd() {
        return this.idCd;
    }

    public void setIdCd(int idCd) {
        this.idCd = idCd;
    }

    @Column(name = "title", nullable = false, length = 45)
    public String getTitle() {
        return this.title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "tbCd")
    public Set<TbTrack> getTbTracks() {
        return this.tbTracks;
    }

    public void setTbTracks(Set<TbTrack> tbTracks) {
        this.tbTracks = tbTracks;
    }

}

CDDAO2

package it.tgi.cd.dao2;

import it.tgi.cd.connection2.DBConnection2;
import it.tgi.cd.entities2.TbCd;

import java.util.Iterator;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;

public class CDDAO2 {
    public static void searchCD(String title) {
        Session session = DBConnection2.openConnection();
        String query = "FROM TbCd where title='" + title + "'";
        Query _query = session.createQuery(query);
        List<TbCd> list = _query.list();
        System.out.println(list);

        DBConnection2.closeConnection(session);

    }

}

你能幫我嗎？ 謝謝！

Answer 1

您要在軌道類中添加CD 字符串 ，並且要在CD類中添加所有軌道字符串 。

這是無限遞歸：CD字符串包含一個軌道字符串（以及其他），此軌道字符串包含CD字符串（與開始時相同！），而CD字符串又包含軌道字符串，依此類推。

解決方法是不包括在該方法的曲目TbCd.toString()或不包括該方法中的CD TbTrack.toString() 我建議使用后者，因為組裝CD字符串時可能打算包含所有軌道：

public class TbCd implements java.io.Serializable {
    @Override
    public String toString() {
        return "idCd=" + idCd + ", title=" + title + ", track= " + tbTracks;
    }
}

public class TbTrack implements java.io.Serializable {
    @Override
    public String toString() {
        return "idTrack=" + idTrack + ", title=" + title;
    }
}

Answer 2

當您這樣做時，它非常簡單：

@Override
public String toString() {
    return "idCd=" + idCd + ", title=" + title + ", track= " + tbTracks;
}

它嘗試打印您的TbTrack對象集，該對象還將覆蓋toString方法，以便：

@Override
public String toString() {
    return "idTrack=" + idTrack + ", tbCd=" + tbCd + ", title=" + title;
}

那么發生了什么：

它打印軌道列表，每個軌道的toString方法都被調用，該方法再次打印CD“ tbCD”，它試圖一次又一次地打印軌道uupps STACKOVERFLOW已達到！！！

從TbTrack類的toString中刪除“ tbCD = + tbCD”，一切正常。 而是打印例如titel；）

簡單的解決方法是：

@Override
public String toString() {
    return "idTrack=" + idTrack + ", tbCd.Title=" + tbCd.title + ", title=" + title;
}