问题：
JPA 在双向映射时，会相互包含对方的实例，相互引用，造成递归迭代，堆栈溢出（java.lang.StackOverflowError）。
分析:
在后端向前端传递的时候会将数据序列化，转为json，这时会出现循环引用造成堆栈溢出
解决方案：
解决方法就是在转换json时忽略循环字段。首先确定项目使用的json包是哪一个（jackjson 或 fastjson），寻找相应的注解忽略某一字段。
jackson包对应的相关注解： @JsonIgnoreProperties、@JsonIgnore
fastjson包对应的相关注解： @JSONField(serialize = false)
注意: 在使用注解时一定要注意引入的包是否正确，如果和自己使用的json包不对应的话，注解是不生效的。
附代码：
// 我的项目使用的alibaba的fastjson包
@Data
class SOStudent {
<span class="token comment"><span class="hljs-comment">// ... ...省略其他字段</span></span>
<span class="token annotation punctuation"><span class="hljs-meta">@ManyToOne</span></span><span class="token punctuation">(</span>cascade <span class="token operator">=</span> <span class="token punctuation">{</span>CascadeType<span class="token punctuation">.</span>REFRESH<span class="token punctuation">}</span><span class="token punctuation">,</span> fetch <span class="token operator">=</span> FetchType<span class="token punctuation">.</span>LAZY<span class="token punctuation">)</span>
<span class="token annotation punctuation"><span class="hljs-meta">@JoinColumn</span></span><span class="token punctuation">(</span>name<span class="token operator">=</span><span class="token string"><span class="hljs-string">"classId"</span></span><span class="token punctuation">)</span>
<span class="token annotation punctuation"><span class="hljs-meta">@JSONField</span></span><span class="token punctuation">(</span>serialize <span class="token operator">=</span> <span class="token boolean"><span class="hljs-keyword">false</span></span><span class="token punctuation">)</span>
<span class="token keyword"><span class="hljs-keyword">private</span></span> SOClass <span class="token keyword"><span class="hljs-class"><span class="hljs-keyword">class</span></span></span><span class="token punctuation">;</span>
}
@Data
class SOClass {
@Id
@GeneratedValue
private Long id
<span class="token comment"><span class="hljs-comment">// ... ...省略其他字段</span></span>
<span class="token annotation punctuation"><span class="hljs-meta">@OneToMany</span></span><span class="token punctuation">(</span>cascade<span class="token operator">=</span><span class="token punctuation">{</span>CascadeType<span class="token punctuation">.</span>ALL<span class="token punctuation">}</span><span class="token punctuation">,</span>fetch <span class="token operator">=</span> FetchType<span class="token punctuation">.</span>EAGER<span class="token punctuation">)</span>
<span class="token keyword"><span class="hljs-keyword">private</span></span> List<span class="token generics function"><span class="token punctuation"><</span>SOStudent<span class="token punctuation">></span></span> students<span class="token punctuation">;</span>
}