Like List, initialize the HashMap as empty when class is generated using xsd

[jobas2007]

The current xjc plugin initializes the list to empty when getter is called.

Firstly was trying to use HashMap in XSD and finally was able to achieve it, but the xjc plugin is yet to initialize it. More details are in stack overflow links https://stackoverflow.com/questions/78077708/using-hashmap-in-xsd.

Was advised by Laurent (contributor) to open a issue.

Appreciate quick resolution so that can use updated plugin before prod release. Thanks

[laurentschoelens]

Hi @jobas2007
Thanks for creating the issue as suggested in SO
Could you tell me which version of JAXB is targeted (JAXB 2.3 / 3.x / 4.x) ?
I'll try having a working MRE with details from SO

[mattrpav]

Maps can get really complicated to try to get correct marshal/unmarshal.

A couple key features:

1. Java supports any object being the key (not all languages do, so interop is problematic)
2. Map.Entry is a valid public scoped object to marshal/unmarshal
3. Some map types in various languages support null key and value entries
4. Differentiation between null entries and empty
5. Falling back to xs:anyType is not great, since you lose ability to communicate strongly typed maps (which are generally more desirable these days vs Map<String, Object>

The scheme is more like this:

<element name="Map">
  <complexType>
    <sequence>
      <element name="entries" minOccurs="0" maxOccurs="1">
        <complexType>
          <sequence>
            <element name="entry" type="map:entry" minOccurs="0" maxOccurs="unbounded"/>
          </sequence>
        </complexType>
      </element>
    </sequence>
  </complexType>
</element>  

<complexType name="entry">
  <sequence> 
    <element name="key" minOccurs="0" type="anyType" minOccurs="0" maxOccurs="1"/>
    <element name="value" minOccurs="0" type="anyType" minOccurs="0" maxOccurs="1"/>
  </sequence>
</complexType>

However, the above approach makes doing Maps with simple primitive K,V overly complex.

Explosion looks like this

NOTE: To get this actually correct, the Map would need to convert the to be a of all the various combination of <K,V> Map.Entry types, since Maps shouldn't have mismatched typing across all the contained Map.Entry.

<complexType name="entry" abstract="true" />

<complexType name="stringStringEntry">
  <complexContent>
    <extension base="map:entry">
      <sequence> 
        <element name="key" minOccurs="0" type="string" minOccurs="1" maxOccurs="1"/>
        <element name="value" minOccurs="0" type="string" minOccurs="0" maxOccurs="1"/>
      </sequence>
    </extension>
  </complexContent>
</complexType>

<complexType name="stringIntegerEntry">
  <complexContent>
    <extension base="map:entry">
      <sequence> 
        <element name="key" minOccurs="0" type="string" minOccurs="1" maxOccurs="1"/>
        <element name="value" minOccurs="0" type="int" minOccurs="0" maxOccurs="1"/>
      </sequence>
    </extension>
  </complexContent>
</complexType>

<complexType name="stringLongEntry">
  <complexContent>
    <extension base="map:entry">
      <sequence> 
        <element name="key" minOccurs="0" type="string" minOccurs="1" maxOccurs="1"/>
        <element name="value" minOccurs="0" type="long" minOccurs="0" maxOccurs="1"/>
      </sequence>
    </extension>
  </complexContent>
</complexType>

...

<complexType name="objectObjectEntry">
  <complexContent>
    <extension base="map:entry">
      <sequence> 
        <element name="key" minOccurs="0" type="anyType" minOccurs="1" maxOccurs="1"/>
        <element name="value" minOccurs="0" type="anyType" minOccurs="0" maxOccurs="1"/>
      </sequence>
    </extension>
  </complexContent>
</complexType>

[laurentschoelens]

@jobas2007 : provided PR #518 for this in v4 branch

[jobas2007]

Hi @jobas2007 Thanks for creating the issue as suggested in SO Could you tell me which version of JAXB is targeted (JAXB 2.3 / 3.x / 4.x) ? I'll try having a working MRE with details from SO

Thanks for looking in this right away.
2.3

[laurentschoelens]

It'll need backport then to v2.x branch but will be done with only new namespaces.