presto-parquet/src/main/java/io/prestosql/parquet/dictionary/LongDictionary.java/LongDictionary/LongDictionary
class LongDictionary:    public LongDictionary(DictionaryPage dictionaryPage)
            throws IOException
    {
        super(dictionaryPage.getEncoding());
        content = new long[dictionaryPage.getDictionarySize()];
        LongPlainValuesReader longReader = new LongPlainValuesReader();
        longReader.initFromPage(dictionaryPage.getDictionarySize(), toInputStream(dictionaryPage));
        for (int i = 0; i < content.length; i++) {
            content[i] = longReader.readLong();
        }
    }