JAXB @XmlElements minOccurs = 1

问题描述

所以我想要一个用@XmlElements 注释的列表，如下所示

So I want to have a list to be annotated with @XmlElements like the following

@XmlElements(
        {
            @XmlElement(name = "Apple", type = Apple.class),
            @XmlElement(name = "Orange", type = Orange.class),
            @XmlElement(name = "Mango", type = Mango.class)
        }
)
public List<Fruit> getEntries() {
        return fruitList;
}

我想知道是否有办法强制列表包含至少 1 个元素，因为现在，xsd 看起来像

I am wondering whether there is a way to enforce the list to contain at least 1 element, because right now, the xsd looks like

<xs:complexType name="fruitList">
    <xs:sequence>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element name="Apple" type="tns:apple"/>
        <xs:element name="Orange" type="tns:orange"/>
        <xs:element name="Mango" type="tns:mango"/>
      </xs:choice>
    </xs:sequence>
  </xs:complexType>

推荐答案

假设 Apple、Orange 和 Mango 是 Fruit 的子类，您可能需要使用 @XmlElementRef 注释 entries 属性 对应于 XML 模式中的替换组，而不是 @XmlElements 对应于选择的概念.

Assuming that Apple, Orange, and Mango are subclasses of Fruit you may want to annotate the entries property with @XmlElementRef which corresponds to substitution groups in XML schema, rather than @XmlElements which corresponds to the concept of choice.

@XmlElementRef
public List<Fruit> getEntries() {
        return fruitList;
}

这假设 Apple、Orange 和 Mango 类扩展了 Fruit 类，并使用 @XmlRootElement

This assumes that the Apple, Orange, and Mango classes extend the Fruit class, and are annotated with @XmlRootElement

@XmlRootElement
public class Apple extends Fruit {
   ...
}

更多信息

• http://bdoughan.blogspot.com/2010/11/jaxb-and-inheritance-using-substitution.html
• http://bdoughan.blogspot.com/2010/10/jaxb-and-xsd-choice-xmlelements.html

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