java - 无法写入 HTTP 消息 : org. springframework.http.converter.HttpMessageNotWritableException:

Question

我是 Spring MVC 框架的新手。我正在尝试使用 Hibernate 检索用户详细信息以返回我的 Spring 项目中的对象。我收到以下错误:

WARN : org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver - Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.ppts.mschef.util.api.ApiResponse["object"]->com.ppts.mschef.model.Mischef["user"]->com.ppts.mschef.model.User_$$_jvstb3_6["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.ppts.mschef.util.api.ApiResponse["object"]->com.ppts.mschef.model.Mischef["user"]->com.ppts.mschef.model.User_$$_jvstb3_6["handler"])

谁能告诉这个错误的解决方案？？

Answer 1

This works for me : 
http://www.geekabyte.io/2013/09/fixing-converterhttpmessagenotwritablee.html


The fix is to get Jackson to be able to handle bi-directional references. And this is done by using two Annotations: @JsonManagedReference and @JsonBackReference.

@JsonManagedReference is used to annotate the inverse side while @JsonBackReference maps the owning side of the relationship.

Example :
@Entity
class Parent {

     @Id
     @Column(name="parent_id")
     @GeneratedValue(strategy = GenerationType.AUTO)
     private Long id;

     private String name;
     private Parent wife;

     @OneToMany(mappedBy="parent" cascade = CascadeType.ALL)
     @JsonManagedReference
     private Collection<Child> children = new ArrayList<>();
...
}


@Entity
class Child {
    private String name;

    @ManyToOne
    @JoinColumn(name="parent_id", referencedColumn="parent_id")
    @JsonBackReference
    private Parent parent;
...
}