ObjectMapper writeValueAsString unnecessarily declares throws IOException

It may seem superfluous, but the problem is that under the hood, String is read using StringReader, written using StringWriter: and since these are handled as Reader/Writer, which declare IOExceptions as being thrown the only clean way to remove these would be to duplicate a whole lot of code.
Or, catch unexpected IOException, throw others.

I'll have to think whether this is worth addressing – anyone who really would like to eliminate this, please vote.

The StringWriter.write() does not declare the IOExceptions, so it is guaranteed to never throw an IOException. The StringReader.read() methods do declare IOExcptions. However, looking through the Java source, it looks like IOExceptions are only thrown when a read is attempted after the StringReader has been closed (per the Reader spec). And since Jackson controls the lifecycle of the reader, it should be able to guarantee that IOExceptions never occur.

So I would think that Jackson should be able to catch the IOException, and throw an AssertionError in the impossible case that an exception was thrown.

Fair enough. Same would apply to 'writeValueAsBytes()' as well.

One good thing wrt method signatures is that this change does not change binary compatibility (unlike, say, change of return type; something that caused unexpected problems with one of upgrades), so it's relatively safe change.

Implemented as suggested; will wrap IOException as JsonMappingException, should it ever occur.