最佳JAXB XJC代码生成和具有继承的最佳XML模式 [英] Optimal JAXB XJC code generation and optimal XML schema with inheritance

问题描述

有很多类似的问题集中在一个方面进行优化，但每个解决方案都有一个丑陋的缺点。

There have been a lot of similar questions which focus on one aspect to optimize but each solution had an ugly downside.

假设我想开发一个XML模式（ XSD）允许以下文档并希望使用XJC生成类：

Suppose I want to develop an XML schema (XSD) which allows the following documents and want to generate classes using XJC:

<Catalogue>
    <Book>...</Book>
    <Journal>...</Journal>
    <Book>...</Book>
    ...
</Catalogue>

架构应该为类型层次结构建模（ Book 和 Journal 是 Publication 的子类。当然，这也应该是生成的Java类的
。

The schema should model the type hierarchy (Book and Journal are subclasses of Publication). Naturally, this should also be the case for the generated Java classes.

我尝试了以下的方法，这些方法都有一个重大问题：

I tried the following approches which all have a major issue:

1。）建模目录包含所有可能子类型的 xsd：choice 。

1.) modeling Catalogue to contain a xsd:choice of all possible subtypes.

<xsd:complexType name="Catalogue">
    <xsd:choice maxOccurs="unbounded">
        <xsd:element ref="Book" />
        <xsd:element ref="Magazine" />
    </xsd:choice>
</xsd:complexType>

<xsd:element name="Publication" abstract="true" type="Publication" />
<xsd:element name="Book" type="Book"/>
<xsd:element name="Magazine" type="Magazine"/>

<xsd:complexType name="Publication">
    <xsd:sequence></xsd:sequence>
</xsd:complexType>

<xsd:complexType name="Book">
    <xsd:complexContent>
        <xsd:extension base="Publication">
        </xsd:extension>
    </xsd:complexContent>
</xsd:complexType>
...

这里的问题是我必须提到所有可能的子类型 choice 元素在实际应用程序中可能很多。
一个小问题是，虽然目录属性具有正确的类型列表< Publication> 但它有一个丑陋的名字 bookAndMagazine 。
由于冗余架构定义，不是一个选项！

The problem here is that I have to mention all possible subtypes in the choice element which could be a lot in a real application. A minor issue is that, although the Catalogue attribute has the correct type List<Publication> it has an ugly name bookAndMagazine. Because of the redundant schema definition, not an option!

2。）建模目录包含 xsd：sequence父类的

2.) modeling Catalogue to contain a xsd:sequence of the parent class

<xsd:complexType name="Catalogue">
    <xsd:choice maxOccurs="unbounded">
        <xsd:element ref="Publication" maxOccurs="unbounded"/>
    </xsd:choice>
</xsd:complexType>

这仅适用于XML文档的制定，如< Publication xsi ：type =Book...> 。因此，不是一个选项！

This does only work if the XML documents are formulated like <Publication xsi:type="Book"...> . Thus, not an option!

3。）使用像这里提到的substitutionGroup http://www.xfront.com/ElementHierarchy.html

3.) Use substitutionGroup like mentioned here http://www.xfront.com/ElementHierarchy.html

<xsd:complexType name="Catalogue">
    <xsd:choice maxOccurs="unbounded">
        <xsd:element ref="Publication" maxOccurs="unbounded"/>
    </xsd:choice>
</xsd:complexType>

<xsd:element name="Publication" abstract="true" type="Publication" />
<xsd:element name="Book" type="Book" substitutionGroup="Publication"/>
<xsd:element name="Magazine" type="Magazine" substitutionGroup="Publication"/>

<xsd:complexType name="Publication">
    <xsd:sequence></xsd:sequence>
</xsd:complexType>

<xsd:complexType name="Book">
    <xsd:complexContent>
        <xsd:extension base="Publication">
        </xsd:extension>
    </xsd:complexContent>
</xsd:complexType>
...

这里，代码生成是问题，因为目录映射到列表< JaxbElement<？扩展出版物>> 而非
列出< Publication> 。因此，这也不是一个选择。

Here, the code generation is the issue because the inner element of Catalogue is mapped to List<JaxbElement<? extends Publication>> rather than List<Publication> . Hence, also this isn't an option.

如何将我的所有目标整合在一起？：

How to bring all my objectives together?:

• 规范继承的规范非冗余模式（例如 2。）或 3。））


• 从这个模式生成的简单而干净的Java类以及模型继承的模型（如 2。），部分在 1中。））


• 清理XML文档（不像 2中那样。））


• 标准JAXB的使用，最好没有多少绑定元数据

• canonical, non-redundant schema which models inheritance (such as in 2.) or 3.))
• simple and clean Java classes generated from this schema and which models inheritance (like in 2.) and partly in 1.) )
• clean XML documents (not like in 2.) )
• usage of standard JAXB and preferable not much binding metadata

如果没有符合所有这些目标的解决方案，您更喜欢哪一个？

And if there is no solution which matches all these objectives, which one would you prefer?

推荐答案

我建议使用与你的第一个选项类似的东西，因为我从未见过这个问题的清洁解决方案。

I would suggest using something similar to your first option as I have never seen a cleaner solution to this problem.

XSD

<xs:element name="Publications" minOccurs="0">
  <xs:complexType>
    <xs:sequence>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element name="Magazine" type="magazine"/>
        <xs:element name="Book" type="book"/>
      </xs:choice>
    </xs:sequence>
  </xs:complexType>
</xs:element>

 <xs:complexType name="magazine">
  <xs:complexContent>
   <xs:extension base="publication">
    <xs:sequence>
      <xs:element name="issueName" type="xs:string" minOccurs="0"/>
    </xs:sequence>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

<xs:complexType name="publication">
  <xs:sequence>
    <xs:element name="name" type="xs:string" minOccurs="0"/>
  </xs:sequence>
</xs:complexType>

<xs:complexType name="book">
  <xs:complexContent>
    <xs:extension base="publication">
      <xs:sequence>
        <xs:element name="title" type="xs:string" minOccurs="0"/>
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

JAVA
这是我用来生成的Java代码上面的XSD。

JAVA This is the Java code I used to generate the above XSD.

@XmlElements({
  @XmlElement(name="Magazine", type=Magazine.class),
  @XmlElement(name="Book", type=Book.class)
})
@XmlElementWrapper(name="Publications")
public List<Publication> publications;

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