Jaxb list unmarshalling order

Question

I have an xml file which looks as follows:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Envelope>
    <AttrA>aaa</AttrA>
    <AttrB>bbb</AttrB>
    <Element ID="1">elem1</Element>
    <Element ID="2">elem2</Element>
    ...
    <Element ID="n">elemn</Element>
</Envelope>

And a corresponding Java class:

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {
"attrA",
"attrB",
"elements",
})
@XmlRootElement(name = "Envelope")
public class Envelope implements Serializable, Equals, HashCode, ToString {  
    @XmlElement(name = "AttrA", required = true)
    protected AttrA attrA;
    @XmlElement(name = "AttrB", required = true)
    protected AttrB attrB;
    @XmlElement(name = "Element")
    protected List<Element> elements;

    @OneToMany(targetEntity = Element.class, cascade = {CascadeType.ALL})
    @JoinColumn(name = "ELEMENT_ID")
    public List<Element> getElements() {
        if (elements == null) {
            elements = new ArrayList<Element>();
        }
        return this.elements;
    }
}

The unmarshalling works fine and I also get my elements-list populated with the appropriate elements, but sometimes the Elements are being swapped in the list. E.q. sometimes I get a list with element 1 and 2 swapped or elements 2 and 3 swapped their places. This affects the equals-method later on during the processing of the objects. I cannot figure out what exactly influences the insert order of the elements into the list.

Is there any anotation or some other way to define the insertion order of the elements? Does anybody see any other problems with my code?

Regards, Iryna.

Update: My schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:jxb="http://java.sun.com/xml/ns/jaxb"
           xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           elementFormDefault="qualified" attributeFormDefault="unqualified" jxb:version="1.0">
<xs:element name="Envelope">
    <xs:complexType>
        <xs:sequence>
            <xs:element ref="mynamespace:AttrA"/>
            <xs:element ref="mynamespace:AttrB"/>
            <xs:sequence>
                <xs:element ref="mynamespace:Element" minOccurs="0" maxOccurs="99"/>
            </xs:sequence>
        </xs:sequence>
    </xs:complexType>
</xs:element>
...
<xs:element name="Element">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="ElemAttrA" type="ElemAttrA" maxOccurs="unbounded" />
        </xs:sequence>
        <xs:attribute name="ID" use="required">
            <xs:simpleType>
                <xs:restriction base="xs:positiveInteger">
                    <xs:minInclusive value="1"/>
                    <xs:maxInclusive value="99"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:attribute>
    </xs:complexType>
</xs:element>
</xs:schema>  

My bindings-xjc.xjb:

<?xml version="1.0" encoding="UTF-8"?>
<jaxb:bindings xmlns="http://java.sun.com/xml/ns/jaxb"
               xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
               xmlns:xs="http://www.w3.org/2001/XMLSchema"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
               xmlns:hj="http://hyperjaxb3.jvnet.org/ejb/schemas/customizations"
               xmlns:orm="http://java.sun.com/xml/ns/persistence/orm"
               xmlns:persistence="http://java.sun.com/xml/ns/persistence"
               xmlns:annox="http://annox.dev.java.net" 
               jaxb:extensionBindingPrefixes="hj orm annox persistence">

<jaxb:bindings schemaLocation="envelope.xsd" node="/xs:schema">

    <jaxb:bindings node="//xs:element[@name='Envelope']/xs:complexType/xs:sequence/xs:sequence/xs:element[@ref='mynamespace:Element']">
        <hj:one-to-many>
            <orm:order-by name="ID" />
        </hj:one-to-many>
    </jaxb:bindings>
    ...
</jaxb:bindings>
...
</jaxb:bindings>

Answer 1

This is not an answer, just a few hints too large for the comment.

Knowing JAXB RI code I don't think there's a chance of getting undeterministic order of items in the list. What happens there is quite straightforward, last come - last added.

You tagged the question with hyperjaxb and your class implements interfaces from JAXB2 Basics runtime, this is an indication that you may be using Hyperjaxb.

If this is the case then Blaise has offered a very good theory on what may be happening. Your List may be mapped to the database without the ordering column so the order may not be guaranteed. Check if you have something with @OrderColumn generated. I think this is not generated by default.

Anyway, posting full code of your class and an accompanying test case would be helpful. For Hyperjaxb, use GitHub to post issues:

• https://github.com/highsource/hyperjaxb3/issues

Update

The problem is indeed in the missing @OrderColumn, just as Blaise predicted (good shot!).

In short, you can add this column using the following customization:

<hj:one-to-many>
    <orm:order-column/>
</hj:one-to-many>

Please see the relevant part of the customization guide.

You can also customize it globally:

<jaxb:bindings schemaLocation="schema.xsd" node="/xs:schema">
    <hj:persistence>
        <hj:default-one-to-many>
            <orm:join-column/>
        </hj:default-one-to-many>
    </hj:persistence>
</jaxb:bindings>

Now all the generated @OneToMany will have a @JoinColumn.

Update 2

Customization for @OrderBy (as you have figured out yourself):

<hj:one-to-many>
    <orm:order-by>ID</orm:order-by>
</hj:one-to-many>

A few more references:

• Customizations schema which is based on the
• JPA ORM 2.0 schema

Disclaimer: I am the author of Hyperjaxb.