JsonMappingException : Can not instantiate value of type [simple type, a.b.c.Company] 来自 JSON 字符串；没有单字符串构造函数/工厂方法

Question

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，一切似乎都正常工作，但是当我尝试将数据反序列化为 POJO 时，我得到了一个异常(exception)。

我的印象是，类路径中只需要 spring 注释和 Jackson jar 的存在，至少对于我的 list、get、delete 具有简单参数的方法来说是这样。

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

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;
}
}

这是一个完整的异常(exception):

org.codehaus.jackson.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.jackson.map.deser.std.StdValueInstantiator._createFromStringFallbacks(StdValueInstantiator.java:379)
at org.codehaus.jackson.map.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:268)
at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromString(BeanDeserializer.java:759)
at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:585)
at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2723)
at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1914)
at org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.readInternal(MappingJacksonHttpMessageConverter.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)

更新:添加了公司 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();
    }

}

更新如果我修改 DTO，让 Jackson 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; }    

更新这是 /company/get/1 方法使用 FireFox RESTClient

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
}

我在 /compamy/create 调用中使用了类似的模式(少了“id”和不同的“uid”)，并带有 Content-type=application/json标题

Answer 1

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。希望对你有帮助