Jaxb生成的类使用JAXBElement而不是指定的类型 [英] Jaxb generated class used JAXBElement instead of specified type

问题描述

这个问题有各种各样的问题 - 但我觉得仍然有进一步编目的空间。

This question has been asked in various guises - but I feel there is still room to catalogue this further.

我有一个带有两个元素定义的xsd

I have an xsd with two element definitions

<xs:complexType name="elementA">
   <xs:sequence>
      <xs:element name="date" type="xs:string" minOccurs="0"/>
      <xs:element name="lastXdigits" type="xs:string" nillable="true" minOccurs="0"/>
   </xs:sequence>
</xs:complexType>

这会产生：

protected String date;
@XmlElementRef(name = "lastXdigits", namespace = "http://xxxxxxx", type = JAXBElement.class)
protected JAXBElement<String> lastXDigits;

将xsd更改为：

<xs:element name="lastXdigits" type="xs:string" nillable="true" minOccurs="1"/>

结果为：

protected String date;
@XmlElement(name = "lastXdigits", required = true, nillable = true)
protected String lastXDigits;

并使用：

<xs:element name="lastXdigits" type="xs:string" minOccurs="0"/>

结果为：

protected String date;
@XmlElement(name = "lastXdigits")
protected String lastXDigits;

这对我来说似乎很奇怪。为什么在第一种情况下将lastXDigits生成为JAXBElement类型，为什么String类型在所有情况下都不够用？另外，当jaxb除了名称之外的定义相同时，为什么jaxb应该区别对待这两个元素呢？

This seems extremely odd to me. Why is lastXDigits generated as a JAXBElement type in the first case and why does a String type not suffice in all cases? Also, why should jaxb treat these two elements differently when their definition apart from name are identical?

我正在使用jaxb 2.0.5中的jaxb-xjc ant任务。

I'm using a jaxb-xjc ant task from jaxb 2.0.5.

这看起来多么可疑或者这些差异有充分的理由吗？

Does this look suspicious or is there good justification for these differences?

推荐答案

如果 nillable =true与 minOccurs =0一起只能用 String 来表示值。 null 是什么意思？这是否意味着它是空的，或者它发生了0次？但是我想这只是一个字符串有点没有用。

If nillable="true" together with minOccurs="0" it is impossible to represent the values with just a String. What would null mean? Does it mean that it was null, or that it occurred 0 times? But I guess that is somewhat moot when it comes to just a String.

与空列表比较。空列表肯定与空列表不同。

Compare with empty list. A null list is certainly different to an empty one.

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