Generic method in Java without generic argument

by 
public static <T> T fromXml(Class<T> clazz, String xml) {

Called as:

Thing thing = fromXml(Thing.class, xml);

or more explicitly:

Thing thing = MyClass.<Thing>fromXml(Thing.class, xml);

To be even more confusing you can have constructors that both construct a generic type and have a generic parameter themselves. Can’t remember the syntax and have never seen it used in anger (you are probably better off with a static creation method anyway).

The cast (T) is unsafe, and you can’t write T.class. So include the T.class as an argument (as JAXBContext.newInstance does) and throw a relevant exception if the type is wrong.

public static <T> T fromXml(Class<T> clazz, String xml) {
    try {
        JAXBContext context = JAXBContext.newInstance(clazz);
        Unmarshaller um = context.createUnmarshaller();
        Object obj = um.unmarshal(new StringReader(xml));
        try {
            return clazz.cast(obj);
        } catch (ClassCastException exc) {
             throw new RelevantException(
                 "Expected class "+clazz+
                  " but was "+obj.getClass()
             );
        }
    } catch (JAXBException exc) {
        throw new RelevantException(
            "Error unmarshalling XML response",
            exc
         );
    }
}

I believe the next version of JAXB (in 6u14?) has some convenience methods for this sort of thing in the JAXB class.

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