ZonedDateTime Custom JSON Converter Grails 3.3.0 - json

Question

I am in the process of converting a really old Grails app to the latest version (3.3.0). Things have been a bit frustrating, but I'm pretty close to migrating everything except the JSON and XML marshallers which were previously registered in my BootStrap init.
The previous marshaller registering looked like this:
// register JSON marshallers at startup in all environments
MarshallerUtils.registerMarshallers()
This was defined like this:
class MarshallerUtils {
// Registers marshaller logic for various types that
// aren't supported out of the box or that we want to customize.
// These are used whenever the JSON or XML converters are called,
// e.g. return model as JSON
static registerMarshallers() {
final dateTimeFormatter = ISODateTimeFormat.dateTimeNoMillis()
final isoDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ")
// register marshalling logic for both XML and JSON converters
[XML, JSON].each { converter ->
// This overrides the marshaller from the joda time plugin to
// force all DateTime instances to use the UTC time zone
// and the ISO standard "yyyy-mm-ddThh:mm:ssZ" format
converter.registerObjectMarshaller(DateTime, 10) { DateTime it ->
return it == null ? null : it.toString(dateTimeFormatter.withZone(org.joda.time.DateTimeZone.UTC))
}
converter.registerObjectMarshaller(Date, 10) { Date it ->
return it == null ? null : isoDateFormat.format(it)
}
converter.registerObjectMarshaller(TIMESTAMP, 10) { TIMESTAMP it ->
return it == null ? null : isoDateFormat.format(it.dateValue())
}
}
}
}
During the migration, I ended up converting all instances of org.joda.time.DateTime to java.time.ZonedDateTime:
class MarshallerUtils {
// Registers marshaller logic for various types that
// aren't supported out of the box or that we want to customize.
// These are used whenever the JSON or XML converters are called,
// e.g. return model as JSON
static registerMarshallers() {
final dateTimeFormatter = DateTimeFormatter.ISO_ZONED_DATE_TIME
final isoDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ")
// register marshalling logic for both XML and JSON converters
[XML, JSON].each { converter ->
// This overrides the marshaller from the java.time to
// force all DateTime instances to use the UTC time zone
// and the ISO standard "yyyy-mm-ddThh:mm:ssZ" format
converter.registerObjectMarshaller(ZonedDateTime, 10) { ZonedDateTime it ->
return it == null ? null : it.toString(dateTimeFormatter.withZone(ZoneId.of("UTC")))
}
converter.registerObjectMarshaller(Date, 10) { Date it ->
return it == null ? null : isoDateFormat.format(it)
}
converter.registerObjectMarshaller(TIMESTAMP, 10) { TIMESTAMP it ->
return it == null ? null : isoDateFormat.format(it.dateValue())
}
}
}
}
Unfortunately, after the upgrade to Grails 3.3.0, this marshaller registering doesn't seem to be used at all, no matter what I try to do.
I do know that there is a new "JSON Views" way of doing things, but this particular service has many endpoints, and I don't want to write custom converters and ".gson" templates for all of them, if everything is already in the format I need. I just need the responses to be in JSON and the dates to behave property (be formatted strings).
Instead, what I am finding (compared to the previous behavior, is that the properties which utilize ZonedDateTime are "exploded" in my JSON output. There is an insane amount of garbage date object information that is not needed, and it is not formatted as a simple string as I expect.
I have tried a few things (mostly per recommendations in the offical latest Grails documentation) ---
Custom Converters
Default Date Format
Adding configurations for grails views in application.yml:
views:
json:
generator:
dateFormat: "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
locale: "en/US"
timeZone: "GMT"
Creating this path under "src":
src/main/resources/META-INF/services/grails.plugin.json.builder.JsonGenerator$Converter
And adding a Converter to my domain class which is named in the file above^:
class MultibeamFileConverter implements JsonGenerator.Converter {
final DateTimeFormatter isoDateFormat = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZ").withZone(ZoneId.of("UTC"));
#Override
boolean handles(Class<?> type) {
MultibeamFile.isAssignableFrom(type)
}
#Override
Object convert(Object value, String key) {
MultibeamFile multibeamFile = (MultibeamFile)value
multibeamFile.startTime.format(isoDateFormat)
multibeamFile.endTime.format(isoDateFormat)
return multibeamFile
}
}
In my controller, I have changed:
return multibeamCatalogService.findFiles(cmd, params)
To this (in order to get JSON output in the browser as before):
respond multibeamCatalogService.findFiles(cmd, params), formats: ['json', 'xml']
Unfortuantely, most permutations I can think to try of the above have resulted in errors such as "Could not resolve view". Otherwise, when I am getting a response, the major issue is that the date is not formatted as a string. This function was previously performed by the Marshaller.
I am getting pretty frustrated. Can someone please tell me how to format ZonedDateTime as a simple string (e.g. - "2009-06-21T00:00:00Z") in my JSON output instead of a giant object like this? Simply converting to java.util.Date causes the "Could not resolve view" error to show up again; consequently, that expects me to make a ".gson" view which never ends up showing the format I expect or is empty.
"startTime": {
"dayOfMonth": 26,
"dayOfWeek": {
"enumType": "java.time.DayOfWeek",
"name": "FRIDAY"
},
"dayOfYear": 207,
"hour": 0,
"minute": 0,
"month": {
"enumType": "java.time.Month",
"name": "JULY"
},
"monthValue": 7,
"nano": 0,
"offset": {
"id": "-06:00",
"rules": {
"fixedOffset": true,
"transitionRules": [],
"transitions": []
},
"totalSeconds": -21600
}, ... // AND SO ON FOR_EVAH

Answer 1

The simple answer is to format a ZonedDateTime object you call .format(DateTimeFormatter). It depends what format you want. You can specify your own or use some of the predefined ones in DateTimeFormatter.
I too though would love to know if there's an easy way to say "for every endpoint display it as json". The only way I've found so far is to have this in every controller class, which isn't too bad but seems silly. I'm using respond followed by a return in my controller methods.
static responseFormats = ['json'] // This is needed for grails to indicate what format to use for respond.
Though I still see the error logged, but rest api still appears to work, "Could not resolve view" for any endpoint I hit.