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Hi I am unmarshalling a XML file that has a tag that can contain both a value or a list of elements. I was wondering what the best approach is for unmarshalling this kind of XML. Example:

<attributes>
    <attribute>value1</attribute>
    <attribute>value2</attribute>
    <attribute>value3</attribute>
    <attribute>value4</attribute>
    <attribute>
        <value>value11</value>
        <value>value12</value>
        <value>value13</value>
        <value>value14</value>
        <value>value15</value>
    </attribute>
    <attribute>value5</attribute>
    <attribute>value6</attribute>
</attributes>

I can't change the way of how the XML is build up so I am hoping someone has a answer. Thank you.

Chris
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  • Have you seen http://stackoverflow.com/questions/15078566/jaxb-how-to-unmarshal-a-list-of-objects-of-different-types-but-with-common-pare ? – Gaël J Dec 21 '15 at 09:37
  • I think you'll need to write a custom adapter because you have no discriminator in your XML sample that allows to automatically find the type of an `attribute` element (i.e. list or simple). – Gaël J Dec 21 '15 at 09:45

1 Answers1

2

Basic steps to read-write xml using JaxB / Unmarshaller and XSD

  • Create a valid XSD file of your XML structure. Find here an online generator.

    Will be something like this (but maybe you need to modify manually some detail, in your XML structure seems you can create the Attribute class wrapping several <attribute> but I dont know for sure if you can have more than one <attributes> tag):

    <xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="attributes">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="attribute" maxOccurs="unbounded" minOccurs="0">
          <xs:complexType mixed="true">
            <xs:sequence>
              <xs:element type="xs:string" name="value" maxOccurs="unbounded" minOccurs="0"/>
            </xs:sequence>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

  • Place it in your project folder.

  • Right click XSD file and auto-generate JAXB classes.

  • Use Unmarshaller to populate auto-generated classes from XML file:

    Unmarshaller u = jc.createUnmarshaller();
Attributes attributes = (Attributes) u.unmarshal( new FileInputStream( "yourFile.xml" ) );

That's it... JaxB will take care of classes, attributes, populate, write/read xml...

Community
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Jordi Castilla
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  • I'm curious of what JAXB will generate for a XSD that matches Chris's XML sample. Not sure JAXB can handle unmarshalling without a custom adapter or specific code (no `xsi:type` on `attribute` elements for instance..). – Gaël J Dec 21 '15 at 09:42
  • @Gaël if you read my answer I warn OP about that, I just put the xsd resulting of an automatic building, what helps, but almost never is perfect for concrete needings. – Jordi Castilla Dec 21 '15 at 09:45