spring boot - How to parse different ISO date/time formats with Jackson and java.time?

Question

Our Rest API takes JSON input from several external parties. They all use "ISO-ish" formats, but the formatting of the time zone offset is slightly different. These are some of the most common formats we see:

2018-01-01T15:56:31.410Z
2018-01-01T15:56:31.41Z
2018-01-01T15:56:31Z
2018-01-01T15:56:31+00:00
2018-01-01T15:56:31+0000
2018-01-01T15:56:31+00

Our stack is Spring Boot 2.0 with Jackson ObjectMapper. In our data classes we use the type java.time.OffsetDateTime a lot.

Several developers have tried to achieve a solution that parses all of the above formats, none have been successful. Particularly the fourth variant with a colon (00:00) seems to be unparseable.

It would be great if the solution works without having to place an annotation on each and every date/time field of our models.

Dear community, do you have a solution?

Answer 1

One alternative is to create a custom deserializer. First you annotate the respective field:

@JsonDeserialize(using = OffsetDateTimeDeserializer.class)
private OffsetDateTime date;

And then you create the deserializer. It uses a java.time.format.DateTimeFormatterBuilder, using lots of optional sections to deal with all the different types of offsets:

public class OffsetDateTimeDeserializer extends JsonDeserializer<OffsetDateTime> {

    private DateTimeFormatter fmt = new DateTimeFormatterBuilder()
        // date/time
        .append(DateTimeFormatter.ISO_LOCAL_DATE_TIME)
        // offset (hh:mm - "+00:00" when it's zero)
        .optionalStart().appendOffset("+HH:MM", "+00:00").optionalEnd()
        // offset (hhmm - "+0000" when it's zero)
        .optionalStart().appendOffset("+HHMM", "+0000").optionalEnd()
        // offset (hh - "+00" when it's zero)
        .optionalStart().appendOffset("+HH", "+00").optionalEnd()
        // offset (pattern "X" uses "Z" for zero offset)
        .optionalStart().appendPattern("X").optionalEnd()
        // create formatter
        .toFormatter();

    @Override
    public OffsetDateTime deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        return OffsetDateTime.parse(p.getText(), fmt);
    }
}

I also used the built-in constant DateTimeFormatter.ISO_LOCAL_DATE_TIME because it takes care of the optional fraction of seconds - and the number of fractional digits seems to be variable as well, and this built-in formatter already takes care of those details for you.

---

I'm using JDK 1.8.0_144 and found a shorter (but not much) solution:

private DateTimeFormatter fmt = new DateTimeFormatterBuilder()
    // date/time
    .append(DateTimeFormatter.ISO_LOCAL_DATE_TIME)
    // offset +00:00 or Z
    .optionalStart().appendOffset("+HH:MM", "Z").optionalEnd()
    // offset +0000, +00 or Z
    .optionalStart().appendOffset("+HHmm", "Z").optionalEnd()
    // create formatter
    .toFormatter();

Another improvement you can make is change the formatter to be static final, because this class is immutable and thread-safe.