jaxb：xsd到java，它是一个父元素，可以具有其他两个元素之一

Question

I have a parent element called MESSAGE . The MESSAGE element can carry any kind of OBJECT (usually complexTypes), but only one object at a time. I'm starting from XML files to XSD then to java with something like this:

<xs:element name="MESSAGE">
      <xs:complexType>
        <xs:sequence>
          <xs:element name="OBJECT"/>
            <xs:complexType>
              <xs:sequence>
              <!-- Definition here -->
              </xs:sequence>
        </xs:sequence>
      </xs:complexType>
</xs:element>

I have lots of XML files which have MESSAGE types but contain different OBJECT s. I have produced their equivalent XSDs but only the first one is translated to java using xjc, while the rest are not because of the error Message is already defined . So how can I have generic MESSAGE element in my XSD which can take any OBJECT s?

Answer 1

I asked a similar question to this one once, and I think it would give you an idea how to do this:

How to Override Xsd element inside of parent/extended element

You'll have to extend/restrict your root parent object.

Answer 2

If the element inside MESSAGE must be one of a subset of defined elements, use <choice> .

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="MESSAGE">
    <xsd:complexType>
      <xsd:choice>
        <xsd:element name="A" type="xsd:string"/>
        <xsd:element name="B" type="xsd:string"/>
      </xsd:choice>
    </xsd:complexType>
  </xsd:element>
</xsd:schema>

If the element inside MESSAGE can be any defined element, use <any> .

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="MESSAGE">
    <xsd:complexType>
      <xsd:sequence>
        <any namespace="##targetNamespace"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>
  <xsd:element name="X" type="xsd:string"/>
  <xsd:element name="Y" type="xsd:string"/>
</xsd:schema>

Answer 3

I solved it using the minoccurs and maxoccurs like this. but it doesn't adhere precisely to what i was asking . the accepted answer is better

<xs:element name="MESSAGE">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="A" minOccurs="0" maxOccurs="1"/>
        <xs:complexType>
          <xs:sequence>
          <!-- Definition here -->
          </xs:sequence>
        </xs:complexType>
      </xs:element>
      <xs:element name="B" minOccurs="0" maxOccurs="1"/>
        <xs:complexType>
          <xs:sequence>
          <!-- Definition here -->
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>
</xs:element>

It was a bit cumbersome adding all the elements to one xsd file , but it worked, i have tested it. @Andreas answer seems more readable using <xsd:choice> . i have never used it, but i will look into it.