@Override
  public String toString() {
    return "reader=" + path.toString()
      + (!isFileInfoLoaded()
        ? ""
        : ", compression=" + trailer.getCompressionCodec().getName() + ", cacheConf=" + cacheConf
          + ", firstKey=" + toStringFirstKey() + ", lastKey=" + toStringLastKey())
      + ", avgKeyLen=" + fileInfo.getAvgKeyLen() + ", avgValueLen=" + fileInfo.getAvgValueLen()
      + ", entries=" + trailer.getEntryCount() + ", length=" + context.getFileSize();
  }
Opens a HFile.
@param context   Reader context info
@param fileInfo  HFile info
@param cacheConf Cache configuration.
@param conf      Configuration
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java