FULL PRODUCT VERSION :
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
JRE 8 contains both, java.time API and JAXB. When trying to marshal / unmarshal java.time.Instant, JAXB fails due to unsupported data type. As java.time is intended to be a replacement for java.util.Date, and as both APIs are part of the same JRE, developers expect this mismatch to be a bug simply.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Execute the program shown below.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Marshals and unmarshals java.time.Instant using ISO UTC format.
ACTUAL -
Fails this exception due to unsupported data type.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" javax.xml.bind.DataBindingException: com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
@XmlAttribute/@XmlValue muss einen Java-Typ referenzieren, der Text in XML zugeordnet ist.
this problem is related to the following location:
at java.time.Instant TimeTest$T.i
at TimeTest$T

at javax.xml.bind.JAXB._marshal(Unknown Source)
at javax.xml.bind.JAXB.marshal(Unknown Source)
at TimeTest.main(TimeTest.java:12)
Caused by: com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
@XmlAttribute/@XmlValue muss einen Java-Typ referenzieren, der Text in XML zugeordnet ist.
this problem is related to the following location:
at java.time.Instant TimeTest$T.i
at TimeTest$T

at com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException$Builder.check(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(Unknown Source)
at com.sun.xml.internal.bind.v2.ContextFactory.createContext(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at javax.xml.bind.ContextFinder.newInstance(Unknown Source)
at javax.xml.bind.ContextFinder.newInstance(Unknown Source)
at javax.xml.bind.ContextFinder.find(Unknown Source)
at javax.xml.bind.JAXBContext.newInstance(Unknown Source)
at javax.xml.bind.JAXBContext.newInstance(Unknown Source)
at javax.xml.bind.JAXB$Cache.<init>(Unknown Source)
at javax.xml.bind.JAXB.getContext(Unknown Source)
... 3 more


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.StringReader;
import java.time.Instant;

import javax.xml.bind.JAXB;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;

public class TimeTest {
    public static void main(String[] a) {
        T t = new T();
        t.i = Instant.now();
        JAXB.marshal(t, System.out);
        System.out.println(JAXB.unmarshal(new StringReader("<T i=\"2014-05-05T11:05:00.000Z\"/>"), T.class).i);
    }

    @XmlRootElement
    public static class T {
        @XmlAttribute
        Instant i;
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use explicit marshalling / unmarshalling code at each place where java.time API is to be used with JAXB.

        @XmlAttribute
        public String getI() {
            return this.i.toString();
        }

        public void setI(String i) {
            this.i = Instant.parse(i);
        }