toString方法和java.lang.StackOverflowError

最新推荐文章于 2023-12-04 15:32:09 发布

转载最新推荐文章于 2023-12-04 15:32:09 发布 · 912 阅读

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CC 4.0 BY-SA版权

原文链接：https://my.oschina.net/ChiLin/blog/711361

文章标签：

#java #数据结构与算法

本文探讨了Java中使用ORM框架进行实体关联映射时可能遇到的问题，特别是针对一对多和一对一关系处理不当导致的StackOverflowError错误。通过具体代码示例展示了News与NewsDetails类之间的相互引用如何形成无限递归。

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下面两个类关联：

News：

package com.lin.springdata.entities;

import java.io.Serializable;
import java.util.Collection;
import java.util.Date;
import java.util.LinkedList;

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.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name="TB_NEWS")
public class News implements Serializable {
	
	private static final long serialVersionUID = 4713558903448287254L;

	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	
	@Column(name = "title",nullable=false)
	private String title;
	
	@Column(name="content",nullable=false)
	private String content;
	
	@Column(name="createDate",nullable=false)
	private Date createDate;
	
	@OneToOne(fetch=FetchType.LAZY, mappedBy="news",cascade=CascadeType.ALL)
	private NewsDetails newsDetails;
	
	@OneToMany(fetch = FetchType.EAGER, mappedBy = "news", cascade = CascadeType.ALL)
	private Collection<Comment> comments = new LinkedList<>();

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getTitle() {
		return title;
	}

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

	public String getContent() {
		return content;
	}

	public void setContent(String content) {
		this.content = content;
	}

	public Date getCreateDate() {
		return createDate;
	}

	public void setCreateDate(Date createDate) {
		this.createDate = createDate;
	}
	
	public NewsDetails getNewsDetails() {
		return newsDetails;
	}

	public void setNewsDetails(NewsDetails newsDetails) {
		this.newsDetails = newsDetails;
	}

	public Collection<Comment> getComments() {
		return comments;
	}

	public void setComments(Collection<Comment> comments) {
		this.comments = comments;
	}

	@Override
	public String toString() {
		return "News [id=" + id + ", title=" + title + ", content=" + content
				+ ", createDate=" + createDate + ", newsDetails=" + newsDetails
				+ ", comments=" + comments + "]";
	}

}

NewsDetails：

package com.lin.springdata.entities;

import java.io.Serializable;

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.OneToOne;
import javax.persistence.Table;

@Table(name="TB_NEWS_DETAILS")
@Entity
public class NewsDetails implements Serializable {

	private static final long serialVersionUID = -2559429260718718580L;
	
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	
	@Column(name="details",nullable=false)
	private String details;
	
	@OneToOne(cascade = {CascadeType.PERSIST, CascadeType.REMOVE},fetch=FetchType.LAZY)
	@JoinColumn(name="news_id",unique=true)
	private News news;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getDetails() {
		return details;
	}

	public void setDetails(String details) {
		this.details = details;
	}

	public News getNews() {
		return news;
	}

	public void setNews(News news) {
		this.news = news;
	}

	@Override
	public String toString() {
		return "NewsDetails [id=" + id + ", details=" + details + ", news="
				+ news + "]";
	}

}

News和NewsDetails的toString方法都被覆写了，直接输出news和newsDetails对象时会调用他们的toString方法。在news的toString中输出newsDetails时，调用newsDetails的toString方法，在newsDetails的toString中又输出news，又调用news的toString方法，所以这种递归调用得不到终止，就会报java.lang.StackOverflowError。

转载于:https://my.oschina.net/ChiLin/blog/711361