BufferedMutator getBufferedMutator(ImmutableBytesWritable tableName) throws IOException {
      if (this.connection == null) {
        this.connection = ConnectionFactory.createConnection(conf);
      }
      if (!mutatorMap.containsKey(tableName)) {
        LOG.debug("Opening HTable \"" + Bytes.toString(tableName.get()) + "\" for writing");

        BufferedMutator mutator = connection.getBufferedMutator(TableName.valueOf(tableName.get()));
        mutatorMap.put(tableName, mutator);
      }
      return mutatorMap.get(tableName);
    }
the name of the table, as a string
@return the named mutator if there is a problem opening a table
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/MultiTableOutputFormat.java