@Override
      public void onException(RetriesExhaustedWithDetailsException e, BufferedMutator mutator) {
        for (int i = 0; i < e.getNumExceptions(); i++) {
          LOG.info("Failed to sent put " + e.getRow(i) + ".");
        }
      }
a callback invoked when an asynchronous write fails.
hbase-examples/src/main/java/org/apache/hadoop/hbase/client/example/BufferedMutatorExample.java