Unmarshalling list of objects using castor gives java.lang.IllegalArgumentException: object is not an instance of declaring class

Question

I'm using castor 1.3.3-rc1 and I've been puzzled with this problem. Have read the manuals few times and I believe I've done everything right here, but I keep getting :

java.lang.IllegalArgumentException: object is not an instance of declaring class{File: [not available]; line: 4; column: 43}

when unmarshalling my xml.

These are my java classes:

public class ReportConfiguration {
    private List<ColumnMapping> columnMappings;

    // getters and setters omitted
}

public class ColumnMapping {
    private int index;
    private String label;
    private String sumTotal;

    // getters and setters omitted
}

This is my xml data file which will be unmarshalled into java classes above

<reportConfiguration>
    <columnMappings>
        <columnMapping index="0" label="Login"/>
        <columnMapping index="1" label="Group"/>
        <columnMapping index="2" label="Profit" sumTotal="yes"/>
    </columnMappings>
</reportConfiguration>

And this is my castor mapping file

<mapping>
    <class name="my.company.ReportConfiguration">
        <map-to xml="reportConfiguration"/>
        <field name="columnMappings" collection="arraylist" type="my.company.ColumnMapping">
            <bind-xml name="columnMappings"/>
        </field>
    </class>

    <class name="my.company.ColumnMapping">
        <map-to xml="columnMapping"/>
        <field name="index" type="integer" required="true">
            <bind-xml name="index" node="attribute"/>
        </field>
        <field name="label" type="string" required="true">
            <bind-xml name="label" node="attribute"/>
        </field>
        <field name="sumTotal" type="string">
            <bind-xml name="sumTotal" node="attribute"/>
        </field>
    </class>
</mapping>

I used Spring OXM, created a org.springframework.oxm.castor.CastorMarshaller instance on my application context, and injected an Unmarshaller instance as dependency. When unmarshalling I just do something like this:

ReportConfiguration config = (ReportConfiguration) unmarshaller.unmarshall(new StreamSource(inputStream));

Can anyone spot what did I do wrong / how else I can debug this problem ?

Answer 1

Ah actually I found the answer. I need to supply container="false" attribute on the castor mapping :

<field name="columnMappings" collection="arraylist" type="my.company.ColumnMapping" container="false">
        <bind-xml name="columnMappings"/>
</field>

This is what castor manual says:

container Indicates whether the field should be treated as a container, i.e. only it's fields should be persisted, but not the containing class itself. In this case, the container attribute should be set to true (supported in Castor XML only).

I think the default is true -- in which case castor hopes to find multiple instance of <columnMapping> directly under <reportConfiguration>, not contained inside a <columnMappings>

A more helpful error message could be presented.