编辑：这似乎也在PUT中发生。

使用spring-data-rest-webmvc版本2.1.0.BUILD-
SNAPSHOT我发现我无法发布具有指向现有资源的关系的资源。我有2个这样的实体，它们需要实例化引用，并且对它们的两个端点之一进行POST都会导致以下行为。

在没有必需引用的情况下发布资源效果很好。

我做了一些挖掘，PersistentEntityResourceHandlerMethodArgumentResolver发现它看起来还MappingJackson2HttpMessageConverter不错，但是最终在检查ObjectMappercan
是否可以反序列化类型时抛出异常。引起异常的原因是NullPointerException。

带/ reservations关系的示例POST：

{ "description" : "test_post", "dateMade" : "2014-03-03T08:04:44.293-0600", "timeLastChanged" : null, "userLastChanged" : null, "courseTypeId" : null, "numCredits" : null, "instructor" : null, "numParticipants" : null, "reservationType" : "MCU", "status" : "REQUESTED", "abstract" : null, "requestor" : "http://localhost:8080/users/2", "submitter" : "http://localhost:8080/users/2", "conferences" : [] }

响应：

{ cause: null message: "No suitable HttpMessageConverter found to read request body into object of type class domain.Reservation from request with content type of application/json!" }

与/ roomGroups无关的POST：

{ "description" : "All Rooms", "isOffNetwork" : false, "roomGroupType" : "STANDARD" }

响应：

201 Created

我正在发布的JSON是否存在问题，导致产生NPE
ObjectMapper？有某种解决方法吗？这在2.0.0.RC1中为我工作，使用了稍微不同的方案在JSON中包括引用链接，并且由于杰克逊依赖项的版本似乎保持不变，所以我想知道是什么导致了此问题…

谢谢你的帮助！

更新：

现在，此问题 似乎 与关联实体无关…

我创建了一个新的@EntityConnectionRequest，如下所示：

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

@Column(name = "FROM_ENTITY_ID", nullable = false)
private Long fromId;

@Column(name = "TO_ENTITY_ID", nullable = false)
private Long toId;

@Convert(converter = EntityTypeConverter.class)
@Column(name = "FROM_ENTITY_TYPE_ID", nullable = false)
private EntityType fromType;

@Convert(converter = EntityTypeConverter.class)
@Column(name = "TO_ENTITY_TYPE_ID", nullable = false)
private EntityType toType;

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE})
@JoinColumn(name = "CONFERENCE_ID", nullable = false)
private Conference conference;

我可以通过json这样包含的会议关系来发布新的ConnectionRequest记录{"conference" : ".../conferences/1"}。

但是，我仍然收到与此@Entity预订相同的异常：

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

@Column(name = "DESCRIPTION", length = 50, nullable = false)
private String description;

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "DATE_MADE", nullable = false)
private Date dateMade;

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "TIME_LAST_CHANGED")
private Date timeLastChanged;

@Column(name = "USER_LAST_CHANGED")
private Integer userLastChanged; // TODO why is this an int?

@Column(name = "ABSTRACT", length = 2000)
private String _abstract;

@Column(name = "COURSE_TYPE_ID")
private Integer courseTypeId;

@Column(name = "NUMBER_OF_CREDITS")
private Integer numCredits;

@Column(name = "INSTRUCTOR", length = 255)
private String instructor;

@Column(name = "NUMBER_OF_PARTICIPANTS")
private Integer numParticipants;

@Convert(converter = ReservationTypeConverter.class)
@Column(name = "RESERVATION_TYPE_ID", nullable = false)
private ReservationType reservationType;

@Convert(converter = StatusConverter.class)
@Column(name = "STATUS_ID") 
private Status status;

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE})
@JoinColumn(name="REQUESTOR_USER_ID", nullable=false)
private User requestor;

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE})
@JoinColumn(name="SUBMITTER_USER_ID", nullable=false)
private User submitter;

@OneToMany(fetch = FetchType.LAZY, mappedBy = "reservation", cascade = {CascadeType.REMOVE})
private Set<Conference> conferences = new HashSet<>();

我不确定这堂课有什么特别之处，导致事情出了问题…