GenericDatumWriter does not support native ByteBuffers

An exception is thrown when trying to encode bytes backed by a file.

java.lang.UnsupportedOperationException: null
at java.nio.ByteBuffer.arrayOffset(ByteBuffer.java:968) ~[na:1.6.0_31]
at org.apache.avro.io.BinaryEncoder.writeBytes(BinaryEncoder.java:61) ~[avro-1.6.3.jar:1.6.3]

Note arrayOffset is an optional method, see:
http://docs.oracle.com/javase/6/docs/api/java/nio/ByteBuffer.html#arrayOffset%28%29

FileChannel returns native ByteBuffer not HeapedByteBuffer

See here:
http://mail-archives.apache.org/mod_mbox/avro-user/201202.mbox/%3CCB57F421.6BFE2%25scott@richrelevance.com%3E