The javadoc for java.nio.charset.CharsetEncoder describes an explicit process for it's use, which does not seem to be followed by io.undertow.servlet.spec.ServletPrintWriter.write(CharBuffer ).

This may be contributing to the infinite loop problem that a user is experiencing on the user forums at Wildfly 8 Final - 100% cpu usage, no load, either due to Undertow's ServletPriterWriter or NIO CharsetEncoder.