I have an entity with java.time.Instant
for created data field:
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@EqualsAndHashCode
public class Item {
private String id;
private String url;
private Instant createdDate;
}
I am using com.fasterxml.jackson.databind.ObjectMapper
to save item to Elasticsearch as JSON:
bulkRequestBody.append(objectMapper.writeValueAsString(item));
ObjectMapper
serializes this field as an object:
"createdDate": {
"epochSecond": 1502643595,
"nano": 466000000
}
I was trying the annotation @JsonFormat(shape = JsonFormat.Shape.STRING)
but it doesn't work for me.
My question is how I could serialize this field as 2010-05-30 22:15:52
string?
One solution is to use jackson-modules-java8. Then you can add a JavaTimeModule
to your object mapper:
ObjectMapper objectMapper = new ObjectMapper();
JavaTimeModule module = new JavaTimeModule();
objectMapper.registerModule(module);
By default the Instant
is serialized as the epoch value (seconds and nanoseconds in a single number):
{"createdDate":1502713067.720000000}
You can change that by setting in the object mapper:
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
This will produce the output:
{"createdDate":"2017-08-14T12:17:47.720Z"}
Both formats above are deserialized without any additional configuration.
To change the serialization format, just add a JsonFormat
annotation to the field:
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "UTC")
private Instant createdDate;
You need to set the timezone, otherwise the Instant
can't be serialized properly (it throws an exception). The output will be:
{"createdDate":"2017-08-14 12:17:47"}
Another alternative, if you don't want to (or can't) use java8 modules, is to create a custom serializer and deserializer, using a java.time.format.DateTimeFormatter
:
public class MyCustomSerializer extends JsonSerializer<Instant> {
private DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneOffset.UTC);
@Override
public void serialize(Instant value, JsonGenerator gen, SerializerProvider serializers) throws IOException, JsonProcessingException {
String str = fmt.format(value);
gen.writeString(str);
}
}
public class MyCustomDeserializer extends JsonDeserializer<Instant> {
private DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneOffset.UTC);
@Override
public Instant deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
return Instant.from(fmt.parse(p.getText()));
}
}
Then you annotate the field with those custom classes:
@JsonDeserialize(using = MyCustomDeserializer.class)
@JsonSerialize(using = MyCustomSerializer.class)
private Instant createdDate;
The output will be:
{"createdDate":"2017-08-14 12:17:47"}
One detail is that in the serialized string you're discarding the fraction of second (everything after the decimal point). So, when deserializing, this information can't be recovered (it'll be set to zero).
In the example above, the original Instant
is 2017-08-14T12:17:47.720Z
, but the serialized string is 2017-08-14 12:17:47
(without the fraction of seconds), so when deserialized the resulting Instant
is 2017-08-14T12:17:47Z
(the .720
milliseconds are lost).