[英]NullPointerException when serializing object to Json
我有一个类型为User
(定义如下)的对象,该对象在序列化为Json时会抛出此特定错误:
com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.providenceuniversal.gim.AuthenticationRequest["user"]->com.providenceuniversal.gim.User["lastSeenToLocal"])
User
定义(具有相关的属性和方法):
public class User implements ServerMessage {
//.....
private final @JsonInclude(Include.NON_NULL) Instant lastSeen;
@JsonCreator
User(@JsonProperty("username") String username) {
if (!isValidUsername(username))
throw new IllegalArgumentException("Invalid constructor argument values");
this.username = username.trim();
this.firstName = null;
this.lastName = null;
this.email = null;
this.status = null;
this.joinDate = null;
this.lastSeen = null;
this.dateOfBirth = null;
}
@JsonCreator
User(
@JsonProperty("username") String username,
@JsonProperty("firstName") String firstName,
@JsonProperty("lastName") String lastName,
@JsonProperty("email") String email,
@JsonProperty("status") String status,
@JsonProperty("joinDate") Instant joinDate,
@JsonProperty("lastSeen") Instant lastSeen,
@JsonProperty("dateOfBirth") LocalDate dateOfBirth) {
if (username == null || username.trim().length() == 0)
throw new IllegalArgumentException("Invalid constructor argument values");
this.username = username.trim();
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
this.status = status;
this.joinDate = joinDate;
this.lastSeen = lastSeen;
this.dateOfBirth = dateOfBirth;
}
//.....
public Instant getLastSeen() {
return lastSeen;
}
public LocalDateTime getLastSeenToLocal() {
return getLastSeen().atZone(ZoneId.systemDefault()).toLocalDateTime();
}
从异常可以明显看出,问题是由getLastSeenToLocal()
方法引起的(该方法试图操纵lastSeen
的null
对象),该方法与序列化过程无关。 Jackson是否默认调用所有getter,是否将它们返回的字段列为JsonProperty
,或者(显然)缺少我?
杰克逊默认使用类的getters()。 所以你可以
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