Question

当我尝试对/ users端点执行get请求时遇到问题，而不是返回我想要的内容，而是在下面返回此错误：

2018-07-07 17:00:06.636 ERROR 294108 --- [nio-8080-exec-3] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"])] with root cause

java.lang.StackOverflowError: null
	at java.lang.ClassLoader.defineClass1(Native Method) ~[na:1.8.0_171]
	at java.lang.ClassLoader.defineClass(ClassLoader.java:763) ~

我的端点方法：

 @Override
    public ResponseEntity<List<M>> findAll() {
        List<M> models = repository.findAll();

        if(models == null || models.isEmpty()){
            return ResponseEntity.noContent().build();
        }

        return ResponseEntity.ok(models);
    }

用户模型：

@Entity
@Table(name = "UN_USERS")
public class User extends AbstractModel {

    @Column(name = "USERNAME", unique = true)
    private String username;

    @Column(name = "UUID")
    private String uuid;

    @Column(name = "COINS")
    private long coins;

    @Column(name = "TOKENS")
    private long tokens;

    @ManyToOne
    @JoinColumn(name = "GROUP_ID", nullable = true)
    private Group group;

    //getters & setters... 
}

组模型：

@Entity
@Table(name="UN_GROUPS")
public class Group extends AbstractModel{

    private String prefix;

    @OneToMany(mappedBy = "group")
    private Set<User> users;

    @ManyToMany(mappedBy = "groups")
    private Set<Permission> permissions;
}

什么可能导致此错误，我该如何解决？

Answer 1

通过分析错误消息，这部分专门：

through reference chain: io.union.restapi.domain.Group["users"]->org.hibernate.collection.internal.PersistentSet[0]->io.union.restapi.domain.User["group"]->io.union.restapi.domain.Group["users"]

我们得到了参考链形成一个循环。您已经遇到了Jackson无限递归问题，有几种解决方法。您可以找到一篇不错的文章，其中涵盖了处理方法here

Answer 2

您必须将@JsonIgnore添加到private Group group;，以便杰克逊可以忽略它。否则，杰克逊将尝试序列化group，然后将创建一个从group对象中的User返回到Set<User> users中的Group属性的循环。 / p>

Answer 3

您可以使用@OneToMany（mappedBy =

@OneToMany(mappedBy = "group",cascade = CascadeType.ALL ,fetch = FetchType.LAZY)

StackOverflowError：执行获取请求时为null

3 个答案: