问题
I have a strange issue marshalling an empty object collection to json using jersey with the jaxb based json support. My object looks like
...
@XmlWrapper(name = "stuff") @XmlElement(name = "s")
private List<Foo> foos;
...
Marshaling this to json produces the expected results
... stuff: [{ "s": ... }, { "s": ... }] ...
except when the list is empty. I would expect to see
... stuff: [] ...
but I see
... stuff: [null] ...
instead. Any idea what's wrong? The problem seems to be related to the @XmlElementWrapper annotation, removing it I don't get the the stuff property in the output at all.
回答1:
Are you serializing an empty list, or are you serializing an un-instantiated null object?
ie. I would expect:
private List<Foo> foos; - would serialize to 'stuff: [null]'
and I would also expect:
private List<Foo> foos = new ArrayList<Foo>(); - we serialize to 'stuff: []'
If that isn't the case, you can always direct Jackson (which is the default JSON serializer bundled with Jersey) to omit the writing of bean properties as null value..
回答2:
I would suggest using POJO mapping based on Jackson. I am not sure why you want that intermediate "s" in there, but POJO would produce (and consume) simpler structure:
"stuff" : [ { ... }, { ... } ]
For that you need no annotations with POJO mapping; JAXB annotations are only needed for XML processing, since XML has no natural mechanism to distinguish arrays from objects (unlike JSON).
回答3:
I managed to solve JSON array and primitive field "bug" in Jersey json library. Secret ingredient is JSONConfiguration and ContextResolver magic. See my following post it has a full code example, customized ContextResolver and rest Application class might be somewhat fuzzy logic in first look.
How to serialize Java primitives using Jersey REST
- json array for zero or single-element Java lists
- primitive integer or boolean fields without quotation chars
来源：https://stackoverflow.com/questions/8210011/marshalling-an-empty-collection-to-json-using-jersey