How to maintain order while using @JsonAnyGetter

[ManiSingal]

public class CustomClass {
    private String fieldOne;
    private String fieldTwo;
    private Map<String, String> firstMap;
    private Map<String, String> secondMap;
    private String fieldThree;
    private String fieldFour;
}

Hi, so I have a class which has two Maps. I want to serialize this class using Jackson, but I also want to unwrap the two maps. Now apparently @JsonUnwrapped doesn't seem to work with maps, and you can't have more than one @JsonAnyGetter. So In this scenario, I'm only left with one option, that I create a custom getter that merges the two maps together and then I can use @JsonAnyGetter.

public class CustomClass {
    private String fieldOne;
    private String fieldTwo;
    private Map<String, String> firstMap;
    private Map<String, String> secondMap;
    private String fieldThree;
    private String fieldFour;

    // Constructors, getters, and setters

    @JsonAnyGetter
    public Map<String, String> getCombinedMaps() {
        Map<String, String> combined = new LinkedHashMap<>();
        combined.putAll(firstMap);
        combined.putAll(secondMap);
        return combined;
    }
}

So this works. Now the other constraint I have is that the order of the Json must be in the order that their declared in, i.e.

{
    "fieldOne" : ...,
    "fieldTwo" : ...,
    "Name": "Name", <- firstMap
    "LastName": "LastName", <- firstMap
    "firstMapKey": "firstMapValue" <- secondMap
    "secondMapKey": "secondMapValue" <-secondMap
    "fieldThree" : ...,
    "fieldFour" : ...,
}

So naturally, I thought to use @JsonPropertyOrder,
@JsonPropertyOrder( {"fieldOne", "fieldTwo", "combinedMaps", "fieldThree", fieldFour"})
However it seems that the order is not maintained when we use @JsonAnyGetter with @JsonPropertyOrder. So the only other alternative is that I create a custom serializer, but I'm trying to avoid that. Any help would be greatly appreciated!

[JooHyukKim]

Have you tried using TreeMap, @ManiSingal ?

[JooHyukKim]

Ah sorry, read the description wrong.

[cowtowncoder]

Correct, @JsonAnyGetter contents are not considered "true" properties (plus they are fully dynamic, not known a priori) so none of the ordering-annotations work with it.

Plus, as you have noticed, only one can be specified for a given POJO.

I cannot think of a way to achieve ordering currently, although issues requesting solving issues you outline have existed for a while:

• Why does jackson use the thread-unsafe date class SimpleDateFormat? #171 (@JsonUnwrapped for Maps) -- but I will actually fix this now due to @JsonAnyGetter providing functionality.
• #518 (for ordering @JsonAnyGetter with @JsonPropertyOrder)

The problem in solving these is the dynamic nature of "any properties" vs static nature of regular POJO properties, and sorting used.

One way forward might be, I think, to give some sort of symbolic name to a set of "any properties" (perhaps via new property of @JsonAnyGetter), and make that name taken into account by @JsonPropertyOrder -- so all any-properties could be located as a group relative to "regular" properties.
And then maybe alphabetic should be used by @JsonAnyGetter handler as well (and/or introducing new property for @JsonAnyGetter for that.

I am not sure I will have time to pursue these, but they might help someone else contribute improvements.

[ManiSingal]

Ahh I see, that makes sense. In that case, I might have to rethink the structure of my code then. Anyways thanks for your reply! :)

[cowtowncoder]

Yeah sorry @ManiSingal -- I wish I brought better news. But I do want to be clear on constraints and limitations that exist, and not give false hope (it's so easy to say "but this may change in future" and give impression a change/fix was imminent -- but I don't like giving false impression).

[TLN2]

I managed to solve both your issues (1. custom ordering and 2. multiple use of @JsonAnyGetter in one object) with the following approach, translated to the example of your input class:

@JsonPropertyOrder({"fieldOne", "fieldTwo", "dynamicFields1", "fieldThree", "dynamicFields2", "fieldFour"})
public class CustomClass
{
	// the order that you see in this property list should be generated
	private String fieldOne;
	private String fieldTwo;
	private Map<String, String> firstMap;
	private Map<String, String> secondMap;
	private String fieldThree;
	private Map<String, String> thirdMap;
	private String fieldFour;

	// these "instructions" do that
	public String getFieldOne() { return fieldOne; }
	public String getFieldTwo() { return fieldTwo; }
	@JsonUnwrapped public DynamicFields1 getDynamicFields1() { return new DynamicFields1(); }
	public String getFieldThree() { return fieldThree; }
	@JsonUnwrapped public DynamicFields2 getDynamicFields2() { return new DynamicFields2(); }
	public String getFieldFour() { return fieldFour; }

	public class DynamicFields1
	{
		@JsonAnyGetter
		public Map<String, String> getCombinedMaps()
		{
			Map<String, String> combined=new LinkedHashMap<>();
			combined.putAll(firstMap);
			combined.putAll(secondMap);
			return combined;
		}
	}

	public class DynamicFields2
	{
		@JsonAnyGetter
		public Map<String, String> getMap()
		{
			return thirdMap;
		}
	}
}

I haven't tested this specific code, but I got the approach running in my own project. It works.

[JooHyukKim]

Thank you for sharing, @TLN2 !