JAXB XML适配器未与XmlElements批注类型一起使用

Question

I have a class A, with subclasses B and C. Furthermore I am using the XmlJavaTypeAdapters annotation in the package-info.java file. In it I am specifying adapters for B and C

@XmlJavaTypeAdapters({
    @XmlJavaTypeAdapter(value = BAdapter.class, type = B.class),
    @XmlJavaTypeAdapter(value = CAdapter.class, type = C.class)
})
package xyz;

In a class in package xyz that is to be serialized with JAXB I am writing this:

@XmlElementWrapper(name = "entries")
@XmlElements({ @XmlElement(name = "b-entry", type = B.class),
               @XmlElement(name = "c-entry", type = C.class) })
private List<A> entries = new ArrayList<>();

This construct in general always works when not requiring XML adapters. However, now, it seems to be that JAXB is not using the defined XML adapters for the @XmlElement types. It is trying to serialize "b-entry" and "c-entry" without the adapters, which fails.
I have many other XmlAdapters on package level, they all work unless you use them with @XmlElements.

Is this a bug or a shortcoming of JAXB? Is my approach wrong?
Please note that I have to use the package level annotation, I cannot annotate directly in the class.

Answer 1

Turns out, it is indeed impossible to use @XmlElements together with package level XML adapters or possibly any XML adapter.

I worked around the issue by creating a List<B> as well as a List<C> and then later in code combining them to form a List<A> .

What is most important however for XML adapters to work with list elements: You are not allowed to specify the type attribute of @XmlElement . Leave it out and the XML adapter will work. This means, the type argument of the List has to be the exact type for which you have the adapter.