使用 jersey 将空集合编组为 json
我在使用 jersey 和基于 jaxb 的 json 支持将空对象集合编组为 json 时遇到一个奇怪的问题。我的对象看起来像
...
@XmlWrapper(name = "stuff") @XmlElement(name = "s")
private List<Foo> foos;
...
将其编组到 json 会产生预期的结果，
... stuff: [{ "s": ... }, { "s": ... }] ...
除非列表为空。我本来希望看到
... stuff: [] ...
，但我
... stuff: [null] ...
却看到了。 知道出了什么问题吗？ 问题似乎与 @XmlElementWrapper 注释有关，删除它后我没有得到 stuff 属性的输出。
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.
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评论（3）
您是序列化一个空列表，还是序列化一个未实例化的空对象？
IE。我期望：
并且我也期望：
如果情况并非如此，您始终可以将 Jackson（这是与 Jersey 捆绑在一起的默认 JSON 序列化器）定向到 省略将 bean 属性写入 null 值。。
Are you serializing an empty list, or are you serializing an un-instantiated null object?
ie. I would expect:
and I would also expect:
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..
我建议使用基于 Jackson 的 POJO 映射。我不确定为什么你想要中间的“s”在那里，但 POJO 会产生（并消耗）更简单的结构：
为此，你不需要 POJO 映射的注释； JAXB 注释仅在 XML 处理时需要，因为 XML 没有区分数组和对象的自然机制（与 JSON 不同）。
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:
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).
我设法解决了 Jersey json 库中的 JSON 数组和原始字段“bug”。秘密成分是 JSONConfiguration 和 ContextResolver 魔法。请参阅我的下一篇文章，它有一个完整的代码示例，自定义的 ContextResolver 和其余的 Application 类乍一看可能有点模糊逻辑。
如何使用 Jersey REST 序列化 Java 原语
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