private CSVParser csvParser() throws IOException {
        // Retrieve the CsvReadWorkbookHolder instance from the CsvReadContext.
        CsvReadWorkbookHolder csvReadWorkbookHolder = csvReadContext.csvReadWorkbookHolder();
        // Get the CSV format configuration from the CsvReadWorkbookHolder.
        CSVFormat csvFormat = csvReadWorkbookHolder.getCsvFormat();
        // Determine the ByteOrderMarkEnum based on the character set name.
        ByteOrderMarkEnum byteOrderMark = ByteOrderMarkEnum.valueOfByCharsetName(
            csvReadContext.csvReadWorkbookHolder().getCharset().name());

        // If the configuration mandates the use of an input stream, build the CSV parser using the input stream.
        if (csvReadWorkbookHolder.getMandatoryUseInputStream()) {
            return buildCsvParser(csvFormat, csvReadWorkbookHolder.getInputStream(), byteOrderMark);
        }

        // If a file is provided in the configuration, build the CSV parser using the file's input stream.
        if (csvReadWorkbookHolder.getFile() != null) {
            return buildCsvParser(csvFormat, Files.newInputStream(csvReadWorkbookHolder.getFile().toPath()),
                byteOrderMark);
        }

        // As a fallback, build the CSV parser using the input stream.
        return buildCsvParser(csvFormat, csvReadWorkbookHolder.getInputStream(), byteOrderMark);
    }
Initializes and returns a CSVParser instance based on the configuration provided in the CsvReadContext.
This method determines the appropriate input stream and character set to create the CSV parser.

@return A CSVParser instance for parsing CSV files.
@throws IOException If an I/O error occurs while accessing the input stream or file.
fastexcel-core/src/main/java/cn/idev/excel/analysis/csv/CsvExcelReadExecutor.java