Java Reflection - Getting a Type from an object to instantiate a generic

Question

I've never really used reflection before and am attempting something I'm not sure is possible. Basically, I'm trying to write a method that takes an Object as a parameter, and then attempts to marshal that object regardless of its type. I can't figure out how to get the type to use when instantiating the generic JAXBElement<T> object. Is this possible? My attempt:

String marshalObject(Object obj) { Class c = obj.getClass(); Type t = (Type) c; QName _QNAME = new QName("http://www.acme.com/ImportExport", c.getName()); StringWriter sw = new StringWriter(); try { ObjectFactory of = new ObjectFactory(); JAXBElement<?> jaxElement = new JAXBElement<t>(_QNAME, c, null, obj); JAXBContext context = JAXBContext.newInstance( c ); Marshaller m = context.createMarshaller(); m.marshal( jaxElement, sw ); } catch( JAXBException jbe ){ System.out.println("Error marshalling object: " + jbe.toString()); return null; } return sw.toString(); }

Tom Anderson · Accepted Answer · 2010-11-08 17:41:40Z

The official generics nerd way to do this is to stick a type parameter on the method. You declare it:

<T> String marshalObject(T obj) {

Then when you get the class:

Class<T> c = obj.getClass(); // something like that

Then finally:

JAXBElement<T> jaxElement = new JAXBElement<T>(_QNAME, c, null, obj);

The first suggestion of using a raw type worked for my purposes, but I'll go back and give this a shot to see the "proper" way of doing it. Thanks for the info!

m.nguyencntt · Accepted Answer · 2019-03-21 03:29:14Z

I did simple way as below and it worked:

public static <T> JAXBElement<T> createJaxbElement(T object, Class<T> clazz) { return new JAXBElement<>(new QName(clazz.getSimpleName()), clazz, object); }

matt b · Accepted Answer · 2010-11-08 15:36:49Z

If you don't care what type JAXBElement is of (i.e. you don't care if it's a JAXBElement<String> or JAXBElement<Foo>, then you can simply use the raw type (JAXBElement) and leave off the type parameter. This will generate a warning which you can suppress.

Alex G · Accepted Answer · 2015-05-26 09:20:05Z

If needed, add QName:

private static <T> JAXBElement<T> makeQName(Object obj) { Class c = obj.getClass(); QName qName = new QName("com.ukrcard.xmlMock", obj.getClass().getName()); return new JAXBElement<T>(qName, c, (T) obj); }

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