Using a custom java.time date with Jackson

It look me quite a bit more research to figure out how to use a custom (or lightly custom) time format with Jackson. I required a date format to be deserialised that did not have a colon in the offset. So a date string like 2018-11-05T05:58:00+0000 i.e. +0000 not +00:00.

In the end it is as simple as:

JavaTimeModule javaTimeModule = new JavaTimeModule();
// Make a new formatter that's based on the ISO_LOCAL_DATE_TIME one
DateTimeFormatter formatter = new DateTimeFormatterBuilder()
    .append(DateTimeFormatter.ISO_LOCAL_DATE_TIME)
    .optionalStart()
    // And just add what we need
    .appendOffset("+HHMM", "+0000")
    .optionalEnd()
    .toFormatter();

LocalDateTimeDeserializer deserializer = new LocalDateTimeDeserializer(formatter);
javaTimeModule.addDeserializer(LocalDateTime.class, deserializer);

// Mapper can come from anywhere, manually created or as part of a framwork
ObjectMapper mapper =  ObjectMapper MAPPER = new ObjectMapper();
// Finally use the new time module
mapper.registerModule(javaTimeModule);
// Use mapper to read JSON with our lightly tweaked time format