Jackson 将日期字符串反序列化为 Long

Question

Can Java Jackson deserialize a json string date into a Java Long field (milliseconds from epoch)?

This is an example of json field to be deserialized:

"timestamp": "2022-01-02T03:04:05Z",

and this is the same field in the Java class, with the current annotations:

@JsonFormat(shape = JsonFormat.Shape.NUMBER, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSSXXX", timezone = "UTC")
@JsonProperty("timestamp") 
@JsonPropertyDescription("blah, blah\r\n")
public Long timestamp;

However, an exception happens:

com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot deserialize value of type java.lang.Long from String "2022-01-02T06:49:05Z": not a valid Long value

Any hint? Thanks.

Answer 1

The answer by Maurice is correct, it only suffers from using the notoriously troublesome and long outdated SimpleDateFormat and Date classes. Also the deserialize method is much simpler without them:

@Override
public Long deserialize(JsonParser jsonparser, DeserializationContext context)
        throws IOException, JsonProcessingException {
    String date = jsonparser.getText();
    return Instant.parse(date).toEpochMilli();
}

Answer 2

Use a custom date deserializer like this one:

public class CustomDateDeserializer extends StdDeserializer<Long> {

    private SimpleDateFormat formatter = 
      new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX");

    public CustomDateDeserializer() {
        this(null);
    }

    public CustomDateDeserializer(Class<?> vc) {
        super(vc);
    }

    @Override
    public Long deserialize(JsonParser jsonparser, DeserializationContext context)  
      throws IOException, JsonProcessingException {
        String date = jsonparser.getText();
        try {
            return formatter.parse(date).toInstant().toEpochMilli();
        } catch (ParseException e) {
            throw new RuntimeException(e);
        }
    }
}

Next annotate your field with @JsonDeserialize(using = CustomDateDeserializer.class) .

@JsonDeserialize(using = CustomDateDeserializer.class)
public Long timestamp;