`ArrayListMultimapDeserializer` does not support multimaps inside another object as a property

[magical-l]

CN: (guava module) ArrayListMultimapDeserializer 未支持multimap作为其他对象的属性。
EN: (guava module) ArrayListMultimapDeserializer does not support multimaps inside another object as a property

CN: 在 com.fasterxml.jackson.datatype.guava.deser.multimap.GuavaMultimapDeserializer:209 行（deserializeFromSingleValue(JsonParser p, DeserializationContext ctxt) 方法中），我们将会检查p.getCurrentToken()是否为JsonToken.START_OBJECT。
EN: at com.fasterxml.jackson.datatype.guava.deser.multimap.GuavaMultimapDeserializer:209 (inside the method deserializeFromSingleValue(JsonParser p, DeserializationContext ctxt) ), we will check whether the value of p.getCurrentToken() is JsonToken.START_OBJECT.

若multimap作为json的整体，此时p.getCurrentToken()确实是JsonToken.START_OBJECT。
if we are deserialize the whole json object to a multimap, then p.getCurrentToken() is exactly JsonToken.START_OBJECT.

但若multimap作为另一个对象的属性，如下：
but what if the multimap is a property of another object:

{
    'theMultimapProperty':{
        '@class':'com.google.common.collect.ArrayListMultimap',//or com.google.common.collect.Multimaps$CustomListMultimap ...
        'a': [1,2]
    }
}

此时p.getCurrentToken()将是JsonToken.FIELD_NAME，对应其作为另一对象属性的属性名theMultimapProperty。
then now the value of p.getCurrentToken() would be JsonToken.FIELD_NAME , as the property name for the multimap in the outside object theMultimapProperty.

然后解析失败。
and then the deserialization fails.

jackson version: 2.13.4

[magical-l]

oh, should move to the jackson-datatypes-collections repo.

[cowtowncoder]

It sounds like there may be a problem to solve. But we would need a full reproduction: looks like this might be using polymorphic deserialization, for example. Description alone is not necessarily sufficient to see how to trigger the problem.

[magical-l]

It sounds like there may be a problem to solve. But we would need a full reproduction: looks like this might be using polymorphic deserialization, for example. Description alone is not necessarily sufficient to see how to trigger the problem.

em, here is an example:

static class Outside {
		public Object aProperty;
	}

	public static void main(final String... args) throws JsonProcessingException, JsonMappingException {
		final var mapper = JsonMapper.builder().addModule(new GuavaModule())//
			.activateDefaultTyping(LaissezFaireSubTypeValidator.instance, DefaultTyping.NON_FINAL, As.PROPERTY)//
			.build();
		final var multimap = ArrayListMultimap.create();
		multimap.put("aKey", 1);
		final var outside = new Outside();
		outside.aProperty = multimap;
		final var s = mapper.writeValueAsString(outside);
		System.out.println(s);
		final var r = mapper.readValue(s, Outside.class);
		System.out.println(r);
	}

it will throw a JsonMappingException at com.fasterxml.jackson.datatype.guava.deser.multimap.GuavaMultimapDeserializer#expect:269.

[cowtowncoder]

Ok thank you @magical-l .

[cowtowncoder]

@magical-l Did you actually test this against later versions? I cannot reproduce it with 2.14.2. This is pretty much the first thing one should do before reporting bugs. :-(

[magical-l]

@cowtowncoder
oh! my version is 2.13.4, after I update to 2.14.2, it's passed. it has been fixed! that's great! and sorry about bothering...

[magical-l]

@cowtowncoder
so there is a new but relevant problem now... when the multimap is empty,

	static class Outside {
		public Object aProperty;
	}

	public static void main(final String... args) throws JsonProcessingException, JsonMappingException {
		final var mapper = JsonMapper.builder().addModule(new GuavaModule())//
			.activateDefaultTyping(LaissezFaireSubTypeValidator.instance, DefaultTyping.NON_FINAL, As.PROPERTY)//
			.build();
		final var multimap = ArrayListMultimap.create();
//		multimap.put("aKey", 1);  //now we use an empty multimap
		final var outside = new Outside();
		outside.aProperty = multimap;
		final var s = mapper.writeValueAsString(outside);
		System.out.println(s);
		final var r = mapper.readValue(s, Outside.class);
		System.out.println(r);
	}

then the exception will happen at the same place(expect method):

{"@class":"......$Outside","aProperty":{"@class":"com.google.common.collect.ArrayListMultimap"}}
Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Expecting START_OBJECT to start `MultiMap` value, found END_OBJECT
 at [Source: (String)"{"@class":"com.lanmudata.super4s.indicatorservice.api.support.O2$Outside","aProperty":{"@class":"com.google.common.collect.ArrayListMultimap"}}"; line: 1, column: 143] (through reference chain: com.lanmudata.super4s.indicatorservice.api.support.O2$Outside["aProperty"])
	at com.fasterxml.jackson.datatype.guava.deser.multimap.GuavaMultimapDeserializer.expect(GuavaMultimapDeserializer.java:274)

[cowtowncoder]

Ok. I'll have a look :)