Question

当杰克逊试图将我的数据解析为Json时，我得到了这个例外：

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: packagename.Thing.Stuffs, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->packagename.Stuff[“thing"]->packagename.Thing[“stuffs"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: packagename.Thing.Stuffs, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->packagename.Stuff[“thing"]->packagename.Thing[“stuffs"])

我有以下实体（名称已被Stuff和Thing取代）：

东西：

@Entity
@Table(name = "stuff")
@SQLDelete(sql = "UPDATE stuff SET deleted = 1 WHERE id = ?")
@Where(clause = "deleted = 0")
public class Stuff implements Serializable {

    private Long id;
    private Thing thing;
    private String stuffName;

    @Id
    @Column(name = "id", unique = true, nullable = false)
    @GeneratedValue
    public Long getId() {
        return this.id;
    }

    @ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, optional = false)
    @JoinColumn(name = "thing_id", nullable = false)
    public Thing getThing() {
        return thing;
    }  

    @Transient
    public String getStuffName() {
        return stuffName;
    }

    // Setters and constructor(s) omitted

}

件事：

@Entity
@Table(name = "thing")
public class Thing implements Serializable {

    private Long id;
    private String name;
    private List<Stuff> stuffs;


    @Id
    @Column(name = "id", unique = true, nullable = false)
    @GeneratedValue
    public Long getId() {
        return this.id;
    }

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

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

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "thing_id")
    @JsonIgnore
    public List<Stuffs> getStuffs() {
        return stuffs;
    }


    // Setters and constructor(s) omitted
}

我一直在谷歌搜索这种类型的错误。当json-parser试图解析由于延迟加载而未加载的对象时，似乎会发生这种情况。延迟加载似乎默认开启。我想避免把所有东西都设置为渴望，所以我把@JsonIgnore放了。什么都不改变我。非常感谢帮助，这让我疯狂。

编辑：

在这两个类中添加@JsonIgnore和@Eager给了我另一个问题。一个看起来像这样的例外：

org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.doResolveException Handling of [org.springframework.http.converter.HttpMessageNotWritableException] resulted in Exception java.lang.IllegalStateException: Cannot call sendError() after the response has been committed

在stackoverflow上搜索它给了我：Hibernate and Jackson (java.lang.IllegalStateException: Cannot call sendError() after the response has been committed)

链接基本上是说我应该添加@JsonIgnore，我已经这样做了。

Answer 1

根据评论，您说您使用的是Jackson 1.9.10，您可以通过为访问类型添加@JsonProperty和READ_ONLY属性来使用WRITE_ONLY注释的新语法

所以你可以使用：

@JsonProperty(access = Access.WRITE_ONLY)

使用您的字段定义。

有关详细信息，请查看 Only using @JsonIgnore during serialization, but not deserialization 讨论。

注意：

对于较旧的版本，您可以在类成员getter上使用@JsonIgnore，在其setter上使用@JsonProperty。

Answer 2

也许您的问题是由错误的映射引起的，您不应该在@JoinColumn实体中使用@OneToMany Thing关系，您需要添加mappedBy = "thing"作为参数正确指定关系。

Hibernate上@JsonIgnore的Jsonparsing错误

2 个答案: