Even if started in JavaEE8 Preview Mode :
<property name="ee8.preview.mode" value="true"/>
Wildfly 12 + RestEasy 3.5 Final can't find this MessageBodyWriter (or Reader) :
Such is provided inside this dependecy :
resteasy-json-binding-provider.jar is already provided inside WIldfly 12.
RestEASY 3.5 Final documentation stats that JsonBindingProvider should be automatically loaded :
If you forcefully exclude Jackson with NoJackson annotation an error will appear stating no MessageWrite is found for json media type when serializing objects for Jax-RS.
I debugged a little to try and find out what was happening and I can confirm that in
org.jboss.resteasy.spi.ResteasyProviderFactory at row 2592
JsonBindingProvider won't be discovered
IF you include resteasy-json-binding-provider dependency directly in your project, than JsonBindingProvider will be discovered and used with priority just like Jax-RS 2.1 specs demand.
Of course, I think this is not correct since you should not be forced to include a specific implementation library to use JsonBinding over other implementations.
Even more if this dependency is already delivered with the application server.
Can you reproduce/fix this issue ?