Hello folks! I am trying to deserialize a yaml file with anchors and
references. There are some existing StackOverflow questions along these
lines but the answers aren't quite getting me to the finish line.
Here is my model:
@JsonIdentityInfo(generator = ObjectIdGenerators.None.class)
class YamlScratch {
@JsonProperty("misc")
List<List<String>> misc;
@JsonProperty("contents")
Map<String, Config> contents;
static class Config {
@JsonProperty("header")
String header;
@JsonProperty("labels")
@JsonIdentityInfo(generator = ObjectIdGenerators.None.class)
List<String> labels;
}
}
Here is my YAML:
misc:
- &letters
- Aie
- Bee
- See
- &numbers
- One
- Two
- Three
contents:
letters:
header: "This is a list of phonetic letters"
labels: *letters
numbers:
header: "This is a list of number spellings"
labels: *numbers
moreletters:
header: "this is another copy of the letters"
labels: *letters
The idea is that I have lists that may be referenced more than once in the
"contents" tree, and I'd like to be able to reference them concisely.
I've tried to enable this in my Java code by adding @JsonIdentityInfo to
the "labels" field that will reference these lists. As for the YAML, I
added "&..." anchors to the data that will be referenced, and where it
should appear I added "*..." references. PyYAML seems to confirm this is
the correct YAML usage:
$ python3
>>> import yaml
>>> f = open(
"/Users/johnpassaro/Library/Preferences/IdeaIC2018.3/scratches/scratch.yml")
>>> y = yaml.load(f)
>>> y
{'misc': [['Aie', 'Bee', 'See'], ['One', 'Two', 'Three']], 'contents': {
'letters': {'header': 'This is a list of phonetic letters', 'labels': ['Aie'
, 'Bee', 'See']}, 'numbers': {'header': 'This is a list of number spellings'
, 'labels': ['One', 'Two', 'Three']}}}
With Jackson (2.9), I get an error:
Exception in thread "main"
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot
deserialize instance of java.util.ArrayList out of VALUE_STRING token
at [Source: (File); line: 14, column: 13] (through reference chain:
YamlScratch["contents"]->java.util.LinkedHashMap["letters"]->YamlScratch$Config["labels"])
I tried changing
List<String> labels;
to
Object labels;
just to see how Jackson was treating it: instead of resolving the anchor
reference ("*letters"), it just returns the reference name as as a string
("letters").
One of the StackOverflow questions has an answer
<https://stackoverflow.com/a/40115377/3229874> that mentions the feature
YAMLParser.Feature.USE_NATIVE_OBJECT_ID. That would seem to be exactly what
I need, but that enum value is not present in 2.9.
Is this behavior supported at all? If so, what do I need to do to make it
work?
Many thanks in advance for your help. I'd be happy to post the results on
the relevant SO threads to make sure this information get shared reasonably
widely.
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