[英]NullPointerException when serializing object to Json
我有一個類型為User
(定義如下)的對象,該對象在序列化為Json時會拋出此特定錯誤:
com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.providenceuniversal.gim.AuthenticationRequest["user"]->com.providenceuniversal.gim.User["lastSeenToLocal"])
User
定義(具有相關的屬性和方法):
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();
}
從異常可以明顯看出,問題是由getLastSeenToLocal()
方法引起的(該方法試圖操縱lastSeen
的null
對象),該方法與序列化過程無關。 Jackson是否默認調用所有getter,是否將它們返回的字段列為JsonProperty
,或者(顯然)缺少我?
傑克遜默認使用類的getters()。 所以你可以
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