问题描述

我正在使用 xjc 从 XML 模式生成 Java 对象.我想使用 IDREF 在文档中多次引用同一个元素.我还想将 IDREF 引用的对象限制为特定类型.我想这样做是出于模式验证的目的，但也是为了在 Java 代码中，引用的对象作为特定类型而不是 Object 类型返回.例如，假设我想要一个模式来描述以下内容:

I am generating Java objects from an XML schema using xjc. I would like to reference the same element multiple times within the document using IDREF. I would also like to constrain the objects referenced by IDREF to a specific type. I'd like to do this for the purposes of schema validation, but also so that in the Java code, the referenced object is returned as a specific type instead of type Object. For example, say I want a schema to describe the following:

<teams>
  <team id="team1">
    <coach>coachz</coach>
    <player>homestar</player>
    <player>marzipan</player>
    <player>strongsad</player>
    <player>strongbad</player>
  </team>

  <team id="team2">
    <coach>bubs</coach>
    <player>homesar</player>
    <player>thecheat</player>
    <player>poopsmith</player>
    <player>bubs</player>
  </team>

  <team id="allstars">
    <coach>poopsmith</coach>
    <player>coachz</player>
    <player>bubs</player>
    <player>kingoftown</player>
    <player>strongbad</player>
  </team>
</teams>

<people>
 <person id="coachz">Coach Z</person>
 <person id="homesar">Homesar</person>
 <person id="homestar">Homestar</person>
 <person id="strongbad">Strong Bad</person>
 <person id="strongsad">Strong Sad</person>
 <person id="marzipan">Marzipan</person>
 <person id="bubs">Bubs</person>
 <person id="kingoftown">King of Town</person>
 <person id="poopsmith">The Poopsmith</person>
 <person id="thecheat">The Cheat</person>
</people>

我可以这样定义player:

<xs:element name="player" type="xs:IDREF" maxOccurs="unbounded"/>

但是在 Java 代码中，当我尝试检索一个播放器时，它会作为类型对象返回，我必须将它转换为一个人.那时，如果有人错误地引用了 Team 对象，我就有可能在验证时发现的错误要处理.我想指定如下内容:

but then in the Java code, when I try to retrieve a player it will come back as type object, and I have to cast it to a person. At that point, if someone has mistakenly referenced a Team object, I have errors to deal with that could have been caught at validation. I want to specify something like this:

<xs:element name="player" type="xs:IDREF"reftype="person"maxOccurs="无界"/>

但据我所知，没有办法像我在此处使用人为属性reftype"所做的那样指定类型.这可以使用 IDREF 完成吗?如果没有，还有其他方法吗?

But as far as I can tell, there is no way to specify a type as I have done here with the contrived attribute 'reftype'. Can this be done, using IDREF? If not, is there another method?

推荐答案

您可以简单地将 baseType 绑定应用到您的 player 元素.比如:

You can simply apply baseType binding to your player element. Something like:

<jaxb:bindings node="xsd:element[@name='player']">
    <jaxb:property>
        <jaxb:baseType name="....Person"/>
    </jaxb:property>
</jaxb:bindings>

您可能需要为您的架构找出正确的绑定位置.

You may need to figure out the correct binding location for your schema.

我的代码示例:

架构:

<xsd:complexType name="HJIII-53-A">
    <xsd:sequence>
        <xsd:element name="b" type="xsd:IDREF"/>
        <xsd:element name="b1" type="test:HJIII-53-B"/>
        <xsd:element name="c" type="xsd:IDREFS"/>
        <xsd:element name="c1" type="test:HJIII-53-C" minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
</xsd:complexType>

绑定:

<jaxb:bindings schemaLocation="schema.xsd" node="/xsd:schema">
    <jaxb:globalBindings localScoping="toplevel">
        <jaxb:serializable/>
    </jaxb:globalBindings>
    <jaxb:bindings node="xsd:complexType[@name='HJIII-53-A']//xsd:element[@name='b']">
        <jaxb:property>
            <jaxb:baseType name="org.jvnet.hyperjaxb3.ejb.tests.issuesjpa2.HJIII53B"/>
        </jaxb:property>
    </jaxb:bindings>
    <jaxb:bindings node="xsd:complexType[@name='HJIII-53-A']//xsd:element[@name='c']">
        <jaxb:property>
            <jaxb:baseType name="org.jvnet.hyperjaxb3.ejb.tests.issuesjpa2.HJIII53C"/>
        </jaxb:property>
    </jaxb:bindings>
</jaxb:bindings>

生成的代码:

@XmlElement(required = true, type = Object.class)
@XmlIDREF
@XmlSchemaType(name = "IDREF")
protected org.jvnet.hyperjaxb3.ejb.tests.issuesjpa2.HJIII53B b;
@XmlElement(required = true)
protected org.jvnet.hyperjaxb3.ejb.tests.issuesjpa2.HJIII53B b1;
@XmlList
@XmlElement(required = true, type = Object.class)
@XmlIDREF
protected List<org.jvnet.hyperjaxb3.ejb.tests.issuesjpa2.HJIII53C> c;
protected List<org.jvnet.hyperjaxb3.ejb.tests.issuesjpa2.HJIII53C> c1;

参见:https://svn.java.net/svn/hj3~svn/trunk/ejb/tests/issues-jpa2/src/main/resources/

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