public static ExcelReaderSheetBuilder readSheet(Integer sheetNo, String sheetName,Integer numRows) {
        ExcelReaderSheetBuilder excelReaderSheetBuilder = new ExcelReaderSheetBuilder();
        if (sheetNo != null) {
            excelReaderSheetBuilder.sheetNo(sheetNo);
        }
        if (sheetName != null) {
            excelReaderSheetBuilder.sheetName(sheetName);
        }
        if (numRows !=null) {
            excelReaderSheetBuilder.numRows(numRows);
        }
        return excelReaderSheetBuilder;
    }
Build excel the 'readSheet'
@param sheetNo Index of sheet,0 base.
@param sheetName The name of sheet.
@param numRows The number of rows to read, the default is all, start with 0.
@return
fastexcel-core/src/main/java/cn/idev/excel/FastExcelFactory.java