Elasticsearch - Get locale specific date in Groovy script - datetime

Question

I need to update existing documents of a particular type with a new field. This new field should be set to the local day name of a date given by a datetime field in the document. The date time field is in the format yyyy-MM-dd'T'HH:mm:ss, is in UTC but has no explicit timezone code.
I'd like to do this with Groovy but have no Java experience. I'm guessing I need to:
1) Set the datetime to UTC locale
2) Convert to local locale (set to Europe/London) in this case
3) Get the day name from converted date and set new field (dayname) value with it
If I use the following update_by_query:
POST /myindex/_update_by_query
{
"script": {
"inline": "ctx._source.dayname = Some_function(ctx._source.datetime)"
},
"query": {
"term": {
"_type": "myDocType"
}
}
}
Is there a simple way to do this with a some Groovy functions (replacing Some_function above).
Any hints would be very much appreciated!
UPDATE - Thanks to tim_yates i have the following Sense console code:
POST /rating/_update_by_query
{
"script": {
"inline": "ctx._source.day = Date.parse(\"yyyy-MM-dd'T'HH:mm:ss\", ctx._source.datetime, java.util.TimeZone.getTimeZone('UTC')).format('EEEE', java.util.TimeZone.getTimeZone('Europe/London'))"
},
"query": {
"term": {
"_type": "transaction"
}
}
}
Unfortunately this generates the following error message:
{
"error": {
"root_cause": [
{
"type": "script_exception",
"reason": "failed to run inline script [ctx._source.day = Date.parse(\"yyyy-MM-dd'T'HH:mm:ss\", ctx._source.datetime, java.util.TimeZone.getTimeZone('UTC')).format('EEEE', java.util.TimeZone.getTimeZone('Europe/London'))] using lang [groovy]"
}
],
"type": "script_exception",
"reason": "failed to run inline script [ctx._source.day = Date.parse(\"yyyy-MM-dd'T'HH:mm:ss\", ctx._source.datetime, java.util.TimeZone.getTimeZone('UTC')).format('EEEE', java.util.TimeZone.getTimeZone('Europe/London'))] using lang [groovy]",
"caused_by": {
"type": "missing_property_exception",
"reason": "No such property: java for class: 1209ff7fb16beac3a71ff2a276ac2225f7c4505b"
}
},
"status": 500
}
Though it does work if I remove reference to the getTimeZone - exact Sense console code as follows:
POST /rating/_update_by_query
{
"script": {
"inline": "ctx._source.day = Date.parse(\"yyyy-MM-dd'T'HH:mm:ss\", ctx._source.datetime).format('EEEE')"
},
"query": {
"term": {
"_type": "transaction"
}
}
}
I'm not sure why the getTimeZone method is failing. I've tried "TimeZone.getTimeZone" instead of "java.util.TimeZone.getTimeZone"

Answer 1

The Groovy code (for Java 7) you will need is going to be very similar to this:
Date.parse("yyyy-MM-dd'T'HH:mm:ss", ctx._source.datetime, TimeZone.getTimeZone('UTC'))
.format('EEEE', TimeZone.getTimeZone("Europe/London"))

Answer 2

OK, a bit more research allowed me to understand that tim_yates answer was correct, we just needed to whitelist the Java class required. We did this via:
nano $JAVA_HOME/lib/security/java.policy
and adding:
permission org.elasticsearch.script.ClassPermission "java.util.TimeZone";
...then restart the ES services.
Note this whitelists the class for all users, not just the ES user. See:
https://www.elastic.co/guide/en/elasticsearch/reference/2.2/modules-scripting-security.html