MapFileReader.java 文件源码

/**
 * It a single record from the map file for the given index
 *
 * @param index Index, between 0 and numRecords()-1
 * @return Value from the MapFile
 * @throws IOException If an error occurs during reading
 */
public V getRecord(long index) throws IOException {
    //First: determine which reader to read from...
    int readerIdx = -1;
    for (int i = 0; i < recordIndexesEachReader.size(); i++) {
        Pair<Long, Long> p = recordIndexesEachReader.get(i);
        if (index >= p.getFirst() && index <= p.getSecond()) {
            readerIdx = i;
            break;
        }
    }
    if (readerIdx == -1) {
        throw new IllegalStateException("Index not found in any reader: " + index);
    }

    WritableComparable key = indexToKey.getKeyForIndex(index);
    Writable value = ReflectionUtils.newInstance(recordClass, null);

    V v = (V) readers[readerIdx].get(key, value);
    return v;
}