JAXB avoid JAXBElement<?> - jaxb

Question

I want to generate Java classes with JAXB from a XSD file.
The problem is, that I always get a few classes like this one (namespace removed):
public static class Action {
#XmlElementRefs({
#XmlElementRef(name = "ReportStateCanceled", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "ReportDate", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "ReportStatePreliminary", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "DocumentID", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "ReportStateNotValidated", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "CaseNo", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "PatientID", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "DocumentKey", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "ReportTime", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "ReportHeading", namespace = "http://...", type = JAXBElement.class, required = false),
#XmlElementRef(name = "ReportStateComplete", namespace = "http://...", type = JAXBElement.class, required = false)
})
protected List<JAXBElement<?>> documentKeyOrDocumentIDOrPatientID;
#XmlAttribute(name = "name")
protected String name;
#XmlAttribute(name = "Query")
protected String query;
/**
* Gets the value of the documentKeyOrDocumentIDOrPatientID property.
*
* <p>
* This accessor method returns a reference to the live list,
* not a snapshot. Therefore any modification you make to the
* returned list will be present inside the JAXB object.
* This is why there is not a <CODE>set</CODE> method for the documentKeyOrDocumentIDOrPatientID property.
*
* <p>
* For example, to add a new item, do as follows:
* <pre>
* getDocumentKeyOrDocumentIDOrPatientID().add(newItem);
* </pre>
*
*
* <p>
* Objects of the following type(s) are allowed in the list
* {#link JAXBElement }{#code <}{#link Template.Page.Actions.Action.ReportDate }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
* {#link JAXBElement }{#code <}{#link Template.Page.Actions.Action.ReportTime }{#code >}
* {#link JAXBElement }{#code <}{#link String }{#code >}
*
*
*/
public List<JAXBElement<?>> getDocumentKeyOrDocumentIDOrPatientID() {
if (documentKeyOrDocumentIDOrPatientID == null) {
documentKeyOrDocumentIDOrPatientID = new ArrayList<JAXBElement<?>>();
}
return this.documentKeyOrDocumentIDOrPatientID;
}
/**
* Gets the value of the name property.
*
* #return
* possible object is
* {#link String }
*
*/
public String getName() {
return name;
}
/**
* Sets the value of the name property.
*
* #param value
* allowed object is
* {#link String }
*
*/
public void setName(String value) {
this.name = value;
}
/**
* Gets the value of the query property.
*
* #return
* possible object is
* {#link String }
*
*/
public String getQuery() {
return query;
}
/**
* Sets the value of the query property.
*
* #param value
* allowed object is
* {#link String }
*
*/
public void setQuery(String value) {
this.query = value;
}
/**
* <p>Java class for anonymous complex type.
*
* <p>The following schema fragment specifies the expected content contained within this class.
*
* <pre>
* <complexType>
* <simpleContent>
* <extension base="<http://www.w3.org/2001/XMLSchema>string">
* <attribute name="dateFormat" type="{http://www.w3.org/2001/XMLSchema}string" />
* </extension>
* </simpleContent>
* </complexType>
* </pre>
*
*
*/
#XmlAccessorType(XmlAccessType.FIELD)
#XmlType(name = "", propOrder = {
"value"
})
public static class ReportDate {
#XmlValue
protected String value;
#XmlAttribute(name = "dateFormat")
protected String dateFormat;
/**
* Gets the value of the value property.
*
* #return
* possible object is
* {#link String }
*
*/
public String getValue() {
return value;
}
/**
* Sets the value of the value property.
*
* #param value
* allowed object is
* {#link String }
*
*/
public void setValue(String value) {
this.value = value;
}
/**
* Gets the value of the dateFormat property.
*
* #return
* possible object is
* {#link String }
*
*/
public String getDateFormat() {
return dateFormat;
}
/**
* Sets the value of the dateFormat property.
*
* #param value
* allowed object is
* {#link String }
*
*/
public void setDateFormat(String value) {
this.dateFormat = value;
}
}
As you can see JAXB uses JAXBElement. Such classes are unuseable for me.
After some research I found out that JAXB has troubles with nillable="true" and minOccurs="0" together, but I do not use nillable anywhere. Tough I am sure, that the problem is related with the minOccurs and maxOccurs.
Even if I would know the exact problem it would be a problem because I get the XSD from an external person and I am not allowed to modify it.
The XSD snippet:
<xs:element name="Action" minOccurs="0" maxOccurs="unbounded">
<xs:complexType>
<xs:choice minOccurs="0" maxOccurs="unbounded">
<xs:element name="DocumentKey" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="DocumentID" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="PatientID" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="CaseNo" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="ReportHeading" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="ReportDate" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string" >
<xs:attribute name="dateFormat" type="xs:string" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name="ReportTime" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string" >
<xs:attribute name="timeFormat" type="xs:string" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name="ReportStateNotValidated" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="ReportStatePreliminary" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="ReportStateComplete" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element name="ReportStateCanceled" type="xs:string" minOccurs="0" maxOccurs="1"/>
</xs:choice>
<xs:attribute name="name" type="xs:string" />
<xs:attribute name="Query" type="xs:string" />
</xs:complexType>
</xs:element>
So I searched for another solution.
I always came to the conclusion that I could solve the problem if add a jaxb-binding.xml when I am generating the classes from the XSD.
I tried some bindings, but it never worked.
With this binding I get less JAXBElements, but I get interfaces instead of classes.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
jaxb:extensionBindingPrefixes="xjc"
jaxb:version="2.0">
<xs:annotation>
<xs:appinfo>
<jaxb:globalBindings generateValueClass="false" generateElementProperty="false" >
<xjc:simple />
</jaxb:globalBindings>
</xs:appinfo>
</xs:annotation>
</xs:schema>
And now I am asking if anyone knows a solution?
The best solution would be if someone provides me a working jaxb-binding.xml.
I am using version 2.2.4-2 of the xjc compiler.
Thank you in advance!

Answer 1

The Problem
The problem is that your xs:choice element has maxOccurs="unbounded".
<xs:choice minOccurs="0" maxOccurs="unbounded">
JAXB Spec Reference
Because of this JAXB can't generate individual properties for each option in the choice structure. See "6.12.6 Bind a repeating occurrence model group" of the JAXB 2.2 (JSR-222) specification for more details:
https://jcp.org/en/jsr/detail?id=222
Why it's a Problem
The following XML fragment is valid according to your XML schema and needs to be able to be represented in the generated object model.
<Action>
<DocumentID/>
<PatientID/>
<PatientID/>
<DocumentID/>
</Action>
Work Around
If you ever really don't like a class that JAXB generates you can create your own and specify via a bindings file that JAXB should use it instead of creating a new one.
<jxb:bindings schemaLocation="yourSchema.xsd">
<jxb:bindings node="//xs:element[#name='Action']">
<jxb:class ref="com.example.Action"/>
</jxb:bindings>
</jxb:bindings>

Answer 2

I wrote the Simpify plugin exactly for this problem.
<xs:schema ...
xmlns:simplify="http://jaxb2-commons.dev.java.net/basic/simplify"
jaxb:extensionBindingPrefixes="... simplify">
<xs:complexType name="typeWithReferencesProperty">
<xs:choice maxOccurs="unbounded">
<xs:element name="a" type="someType">
<xs:annotation>
<xs:appinfo>
<simplify:as-element-property/>
</xs:appinfo>
</xs:annotation>
</xs:element>
<xs:element name="b" type="someType"/>
</xs:choice>
</xs:complexType>
will give you
#XmlElement(name = "a")
protected List<SomeType> a;
#XmlElement(name = "b")
protected List<SomeType> b;
instead of
#XmlElementRefs({
#XmlElementRef(name = "a", type = JAXBElement.class),
#XmlElementRef(name = "b", type = JAXBElement.class)
})
protected List<JAXBElement<SomeType>> aOrB;
Disclaimer: I'm the author.