UnsupportedOperationException from createXMLStreamReader ⇒ fall back to overloads guaranteed to work

[jglick]

Alternative to #480. Rather than throwing an error, or forcing clients to use a new API, automatically and silently fall back to the provided StAX implementation (presumably from the JRE) even if it is not as nice as Woodstox.

Untested.

[basil]

As detailed in FasterXML/jackson-dataformat-xml#480 (comment) I tested the ByteArrayInputStream change in a realistic environment: Jenkins core 2.300, where a plugin's thread context classloader (which is core's web application class loader) does not have Woodstox, but the plugin's classloader does have Woodstox. Before this change, I got the UnsupportedOperationException. After this change, it worked. I verified by stepping through the change in the debugger that we were successfully catching the UnsupportedOperationException and that retrying against the JRE's built-in class worked.

[cowtowncoder]

I think I could work with this; I think it may be possible to dynamically detect likelihood of support.
Stax2 api has wrapper used for non-native implementations, and such wrapping probably means stax2 byte source won't work...

[cowtowncoder]

Thank you @jglick and @basil! I think that this behavior (exception) was a flaw -- although it is strongly recommended Woodstox or other Stax2-implementing library is used, I'd like to avoid unnecessary failures for other implementations, esp. one bundled in JDK. So good catch, thank you reporting it.

I changed implementation slightly via #482, to avoid throwing exception, since I figured an alternative based on checking for XMLInputFactory2 (stax2 api); the effect should be same here. Also added a test to verify this.

I guess there is still open question on whether #480 (or something along those lines) should be added too, so I'll leave that open. But I think I can close this PR.

Fix should go in 2.12.4 whenever I release that (probably to after 2.13.0-rc1), hopefully within a month -- I need to release a full set and it's likely the last 2.12 patch.