OK, #1, can you try doing an experiment with "cp -r <src-path>
<dest-path>", and tell me whether the copy speed is faster or slower,
and whether the CPU utilization is faster or slower?  Even if it's a
bit slower to use cp -r, it will be easier for us to try to reproduce
things and to understand what cp -r is doing as opposed to some
mystery java program.

#2, if you know how to set up ftrace, can you enable the
ext4_mballoc_alloc tracepoint and send me a sample output (a few
hundred lines will be plenty).

The short version is basically:

<start your java copy program>
echo 1 > /sys/kernel/debug/tracing/events/ext4/ext4_mballoc_alloc/enable
<wait 30 seconds>
cat /sys/kernel/debug/tracing/trace > /var/tmp/trace-save
echo 0 > /sys/kernel/debug/tracing/events/ext4/ext4_mballoc_alloc/enable

						- Ted