`float[]` and `double[]` are serialized to JSON as `{ }`

[lukehutch]

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Describe the bug

float[] and double[] are serialized to JSON as { }.

Version Information

jackson-jr-objects 2.18.3

Reproduction

The following code:

var values = new LinkedHashMap<String, Object>();
values.put("intArray", new int[] { 1, 2, 3 });
values.put("longArray", new long[] { 1L, 2L, 3L });
values.put("floatArray", new float[] { 1.0f, 2.0f, 3.0f });
values.put("doubleArray", new double[] { 1.0, 2.0, 3.0 });
System.out.println(JSON.std.with(JSON.Feature.PRETTY_PRINT_OUTPUT).asString(values));

prints:

{
  "intArray" : [ 1, 2, 3 ],
  "longArray" : [ 1, 2, 3 ],
  "floatArray" : { },
  "doubleArray" : { }
}

Expected behavior

{
  "intArray" : [ 1, 2, 3 ],
  "longArray" : [ 1, 2, 3 ],
  "floatArray" : [ 1.0, 2.0, 3.0 ],
  "doubleArray" : [ 1.0, 2.0, 3.0 ]
}

[pjfanning]

try 2.18.4 - it includes a bug fix that may help here

[lukehutch]

@pjfanning Thanks, but that doesn't fix it.

[pjfanning]

This should really be moved to https://github.com/FasterXML/jackson-jr

[pjfanning]

I tested this with jackson-databind and see no issue. I am not very familiar with jackson-jr but the code there is somewhat different to what is in jackson-databind.

[pjfanning]

I reproduced this in jackon-jr-objects but claim no expertise in terms of solving it.
The float array seems to be written as {} even if written directly as opposed to being inside a Map instance.
JSON.std.asString(new float[] { 1.0f, 2.0f, 3.0f }) returns {}

[pjfanning]

jackson-jr/jr-objects/src/main/java/com/fasterxml/jackson/jr/ob/impl/ValueLocatorBase.java

Line 61 in ac11c97

public final static int SER_INT_ARRAY = 5;

From the jackson-jr code above, it appears that there is support for certain types of array but float and double arrays are not supported. I suppose this could be added but jackson-jr is meant to be small so there might be a good reason why they are not supported yet.

[cowtowncoder]

Yes, I think support exists for int[] and long[], as demonstrated by test.

As usual, PRs welcome; it's just a gap. But note that deserialization also needs to be added if serialization is.

[lukehutch]

Feel free to move this over to the jackson-jr repo (sorry, I didn't realize that was separate, and I can't move it).

I'm on a tight timeline, so won't be able to submit a PR, but thanks for tracking down the source of the issue!

[lukehutch]

Since number is represented internally as double in JS, I would think that double[] should be the first thing supported by a JSON serializer -- so this is probably just an accidental omission. (float[] should also be supported, of course...)

I doubt the reason this was left out was to keep jackson-jr small... they probably just forgot about it and didn't have testcases covering it.

[cowtowncoder]

It literally was laziness. I am fully aware support is missing for some types such as boolean[], short[] too 😀

…

On Tue, Jun 17, 2025 at 11:46 AM Luke Hutchison ***@***.***> wrote: *lukehutch* left a comment (FasterXML/jackson-jr#196) <#196 (comment)> Since number is represented internally as double in JS, I would think that double[] should be the first thing supported by a JSON serializer -- so this is probably just an accidental omission. (float[] should also be supported, of course...) I doubt the reason this was left out was to keep jackson-jr small... they probably just forgot about it and didn't have testcases covering it. — Reply to this email directly, view it on GitHub <#196 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAANOGJYHPF7TW4WTGAA7Z33EBPAZAVCNFSM6AAAAAB7QSAPAGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSOBRGQ3TGMRVGY> . You are receiving this because you commented.Message ID: ***@***.***>

[cowtowncoder]

Note though that regular double/Double, float/Float properties are supported. Just not all primitive array types. This because array types are real types unlike Lists and Collections. Requires bit more work esp on deserialization. Finally given how many years passed before support requested, double[] really does not seem to be one of the first types that need support….but good to eventually support of course. On Tue, Jun 17, 2025 at 12:07 PM Tatu Saloranta ***@***.***> wrote:

…

It literally was laziness. I am fully aware support is missing for some types such as boolean[], short[] too 😀 On Tue, Jun 17, 2025 at 11:46 AM Luke Hutchison ***@***.***> wrote: > *lukehutch* left a comment (FasterXML/jackson-jr#196) > <#196 (comment)> > > Since number is represented internally as double in JS, I would think > that double[] should be the first thing supported by a JSON serializer > -- so this is probably just an accidental omission. (float[] should also > be supported, of course...) > > I doubt the reason this was left out was to keep jackson-jr small... they > probably just forgot about it and didn't have testcases covering it. > > — > Reply to this email directly, view it on GitHub > <#196 (comment)>, > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/AAANOGJYHPF7TW4WTGAA7Z33EBPAZAVCNFSM6AAAAAB7QSAPAGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSOBRGQ3TGMRVGY> > . > You are receiving this because you commented.Message ID: > ***@***.***> >