@Override
    public void setup(Context context) throws IOException {
      Configuration conf = context.getConfiguration();
      String[] tables = conf.getStrings(TABLES_KEY);
      this.multiTableSupport = conf.getBoolean(MULTI_TABLES_SUPPORT, false);
      Collections.addAll(tableSet, tables);
    }
A mapper that just writes out KeyValues. This one can be used together with
{@link CellSortReducer}
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/WALPlayer.java