JsonMappingException：无法从 JSON 字符串实例化 [简单类型，abcCompany] 类型的值；没有单字符串构造函数/工厂方法

JsonMappingException: Can not instantiate value of type [simple type, a.b.c.Company] from JSON String; no single-String constructor/factory method

提问by hairyone

I have just added a REST api to my existing Spring + BlazeDS + Hibernate server and everything appears to work when data is retrieved and serialised as JSON but when I try and POST data to be de-serialised into a POJO I get the an exception.

我刚刚向我现有的 Spring + BlazeDS + Hibernate 服务器添加了一个 REST api，当数据被检索并序列化为 JSON 时，一切似乎都在工作，但是当我尝试将 POST 数据反序列化为 POJO 时，我得到了一个异常。

I was under the impression that the spring annotations and the presence of the Hymanson jars in the class path would be all that was required, at least it was for my list, get, delete methods that had simple parameters.

我的印象是 spring 注释和类路径中 Hymanson jar 的存在将是所有需要的，至少对于我的具有简单参数的 list、get、delete 方法而言。

org.codehaus.Hymanson.map.JsonMappingException: Can not instantiate value of type [simple type, class com.twoh.dto.Company] from JSON String; no single-String constructor/factory method

Here's the method being called:

这是被调用的方法：

public abstract class BaseEntityService<T extends BaseEntity> implements IBaseEntityService<T> {

private IBaseEntityDAO<T> DAO;

@Autowired
private ValidationResultHelper validationResultHelper;

public void setDAO(IBaseEntityDAO<T> DAO) {
    this.DAO = DAO;
}

...
@Secured("ROLE_USER")
@RequestMapping(value="/create", method=RequestMethod.POST)
public @ResponseBody ValidationResult create(@RequestBody T entity) {
    ValidationResult result = null;
    try {
        result = DAO.persistEntity(entity);
    } catch(JDBCException e) {
        result = ExceptionHelper.getValidationResult(e);
    } catch(DataIntegrityViolationException e) {
        result = ExceptionHelper.getValidationResult(e);
    }
    validationResultHelper.log(DAO.getSession(), entity.getId(), entity.getClass(), result);
    return result;
}
}

and here is the full exception:

这是完整的例外：

org.codehaus.Hymanson.map.JsonMappingException: Can not instantiate value of type [simple type, class com.twoh.dto.Company] from JSON String; no single-String constructor/factory method
at org.codehaus.Hymanson.map.deser.std.StdValueInstantiator._createFromStringFallbacks(StdValueInstantiator.java:379)
at org.codehaus.Hymanson.map.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:268)
at org.codehaus.Hymanson.map.deser.BeanDeserializer.deserializeFromString(BeanDeserializer.java:759)
at org.codehaus.Hymanson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:585)
at org.codehaus.Hymanson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2723)
at org.codehaus.Hymanson.map.ObjectMapper.readValue(ObjectMapper.java:1914)
at org.springframework.http.converter.json.MappingHymansonHttpMessageConverter.readInternal(MappingHymansonHttpMessageConverter.java:135)
at org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:154)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.readWithMessageConverters(HandlerMethodInvoker.java:633)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveRequestBody(HandlerMethodInvoker.java:597)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveHandlerArguments(HandlerMethodInvoker.java:346)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:171)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:436)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:424)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:669)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:585)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:311)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:116)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:101)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:182)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:173)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)

Update: added definition of Company DTO

更新：增加了公司 DTO 的定义

@CheckDictionaryProperty.List({
    @CheckDictionaryProperty(propertyName="partyId", dictionaryName="Party")
})
@Unique.List({
    @Unique(properties = {"code"}, message = "UNIQUE_CODE"),
    @Unique(properties = {"name"}, message = "UNIQUE_NAME")
})
@Entity
@FXClass
@Table(name="edrcompany")
@JsonAutoDetect
public class Company extends BaseEntity {

    private static final long serialVersionUID = 1L;

    public Company(){}

    @NotBlank
    @Column
    private String name;
    public String getName(){ return this.name; }
    public void setName(String name){ this.name = name; }

    @Column
    private String code;
    public String getCode() { return this.code; }
    public void setCode(String code) { this.code = code; }

    @NotNull
    @Column(name="party_id")
    private Integer partyId;
    public Integer getPartyId() { return this.partyId; }
    public void setPartyId(Integer partyId) { this.partyId = ValueHelper.isNullOrZero(partyId) ? null : partyId; }

    @ElementCollection(targetClass=Integer.class, fetch=FetchType.EAGER)
    @Fetch(FetchMode.SUBSELECT)
    @CollectionTable(name="edrcompanyadminlink", joinColumns={@JoinColumn(name="company_id")})
    @Column(name="user_id")
    private Collection<Integer> adminUserIdList = new HashSet<Integer>();
    public Collection<Integer> getAdminUserIdList() { return this.adminUserIdList; }
    public void setAdminUserIdList (Collection<Integer> adminUserIdList) { this.adminUserIdList = adminUserIdList; }    


}


@MappedSuperclass
@FXClass
public abstract class BaseEntity implements Serializable  {

    private static final long serialVersionUID = 1L;

    public BaseEntity(){}

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer id;
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = ValueHelper.isNullOrZero(id) ? null : id; }

    @Column(name="ENTITY_UID", unique=true, nullable=false, updatable=false, length=36)
    /* Assign a default whenever this class is instantiated Hibernate will 
     * overwrite it when retrieving an entity from the DB.
     */
    private String uid = UUID.randomUUID().toString();
    public String getUID() { return uid; };
    public void setUID(String uid) { this.uid = uid; }

    @Version
    @Column
    private Integer version;
    @FXIgnore
    public Integer getVersion() { return this.version; }
    public void setVersion(Integer version) { this.version = version; }

    // Fake property so that DTO2FX will put it in
    public String getClassName() { return this.getClass().getName(); }
    @JsonIgnore
    public void setClassName(String className) { throw new UnsupportedOperationException(); }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;

        if (o == null || !(o instanceof BaseEntity)) return false;

        BaseEntity other = (BaseEntity) o;

        // if the id is missing, return false
        if (uid == null) return false;

        // equivalence by uid
        return uid.equals(other.getUID());
    }

    @Override
    public int hashCode() {
        if (uid != null) {
            return uid.hashCode();
        } else {
            return super.hashCode();
        }
    }

    @Override
    public String toString() {
        return this.getClassName() + ": " + this.getId();
    }

}

UpdateIf I amend the DTO so that Hymanson ignores the Company.adminUserIdList property then the record is created successfully.

更新如果我修改 DTO 以便 Hymanson 忽略 Company.adminUserIdList 属性，则记录创建成功。

@JsonIgnore
public Collection<Integer> getAdminUserIdList() { return this.adminUserIdList; }
@JsonIgnore
public void setAdminUserIdList (Collection<Integer> adminUserIdList) { this.adminUserIdList = adminUserIdList; }    

UpdateHere is the Json as returned by the /company/get/1method using FireFox RESTClient

更新这是/company/get/1使用 FireFox RESTClient的方法返回的 Json

{
  "partyId":1,
  "adminUserIdList":[21],
  "name":"2H Mechanical LLC",
  "code":null,
  "uid":"fc5e15e7-a9a7-11e1-be90-7d08b05cbb96",
  "id":1,
  "className":"com.twoh.dto.Company",
  "version":0
}

I was using a similar pattern (less the "id" and a different "uid")for the /compamy/createcall with a Content-type=application/jsonheader

我正在使用类似的模式（减去“id”和不同的“uid”）用于/compamy/create带有Content-type=application/json标题的调用

回答by Techky

I solved the same problem by fixing the JSON I was sending to the server; it was invalid. I removed the "," characters at the end of the last attributes and it worked. I hope it helps

我通过修复发送到服务器的 JSON 解决了​​同样的问题；这是无效的。我删除了最后一个属性末尾的“，”字符并且它起作用了。我希望它有帮助

回答by Nirmal Mangal

In my case, I was missing starting and ending curly braces.

就我而言，我缺少开始和结束大括号。

回答by DivDiff

Similar to @Nirmal, I passed in JSON which was contained within double quotes:

与@Nirmal 类似，我传入了包含在双引号中的 JSON：

"{ "SomeJSON":"Value" }"

"{ "SomeJSON":"Value" }"

instead of

代替

{ "SomeJSON":"Value" }

{ "SomeJSON":"Value" }

Removing the "s resolved the issue.

删除"s 解决了问题。

回答by Steve Stilson

Also, I got this error message when I tried to instantiate an enum that wasn't properly defined in my swagger file. See How to define enum in swagger.io?

此外，当我尝试实例化在我的 swagger 文件中未正确定义的枚举时，我收到了此错误消息。请参阅如何在 swagger.io 中定义枚举？