@Override
    protected T doRead() throws Exception { //NO SONAR
        logger.info("Start doRead");
        //check if the givem recource exists
        if (!this.resource.exists()) {
            if (this.strict) {
                throw new IllegalStateException("Input resource must exist (reader is in 'strict' mode): "
                        + this.resource);
            }
            logger.warn("Input resource does not exist '"+this.resource.getDescription()+"'.");
            return null;
        }
        if (isFirstTime) {
            //create the appropriate file pattern deppending on the month number
            //if month < 3 choose current year System's configuration value - 1 (SystemConfiguration.year - 1)
            //else get the current year from the system configuration (SystemConfiguration.year)
            Calendar currentDate = Calendar.getInstance();
            int month = currentDate.get(Calendar.MONTH);

            SystemConfiguration sysConf = sysConfServ.findCurrentSystemConfiguration();//get system configuration
            //get create the patern for the current year
            String currentYearPatternStr = Constants.INST_DOCS_FILES_PATTERN.replace(Constants.INST_DOCS_YEAR_PATTERN, String.valueOf(sysConf.getYear()));


            List<String> patternStrList = new ArrayList<String>();
            patternStrList.add(currentYearPatternStr);
            if (month < 3) { //and if month is < 3 create the pattern for the previous System configuration year
                String previousYearPatternStr = Constants.INST_DOCS_FILES_PATTERN.replace(Constants.INST_DOCS_YEAR_PATTERN, String.valueOf(sysConf.getYear().intValue() - 1));
                patternStrList.add(previousYearPatternStr);
            }

            List<Pattern> patternList = new ArrayList<Pattern>(); //initialize Patterns
            for (String pattern : patternStrList) {
                patternList.add(Pattern.compile(pattern));
            }
            Matcher matcher = null; //and Matcher objects


            //fill the Queue with data
            File[] files = resource.getFile().listFiles();
            if (files != null && files.length != 0) { //if files is not empty
                for (File file : files) {
                    for (Pattern pattern : patternList) { //then, for each file that its name matches with the pattern
                        matcher = pattern.matcher(file.getName());
                        if (matcher.matches()) {
                            filesQueu.add(file); //append it in file-Queue
                        }
                    }
                }
            }
            //if file-queue is empty return null
            if (filesQueu.isEmpty()) {
                isFirstTime = true;
                return null;
            }
            isFirstTime = false;
        }

        //else
        while (!filesQueu.isEmpty()) {

            if (!isReading) {
                File file = filesQueu.peek(); //peek each element from the queue
                currentFileName = file.getName();
                this.openExcelFile(new FileSystemResource(file)); //open file
                this.openSheet(); //get the Sheets
                final Sheet sheet = this.getSheet(this.currentSheet);
                int currentFileRowsNumber = sheet.getNumberOfRows(); //get the number of rows
                currentRow = 0;
            }


            while (currentRow <= currentFileRowsNumber) {



                final String[] row = this.readRow(sheet);  //read row
                //when finish the file reading pop the element
                if (this.currentRow == currentFileRowsNumber) {
                    filesQueu.poll();
                    this.isReading = false;
                }
                if (ObjectUtils.isEmpty(row)) { //if the row is empty, proscceed to the next row
                    currentRow++;
                    continue;
                }else {
                    try {
                        //else, send the data in  InstDocWriter.write() and create a new document instance in database
                        return this.rowMapper.mapRow(sheet, row, this.currentRow, this.currentFileName);
                    } catch (final Exception e) {
                        throw new ExcelFileParseException("Exception parsing Excel file.", e, this.resource.getDescription(),
                                sheet.getName(), this.currentRow, row);
                    }
                }

            }
        }
        logger.info("End doRead");
        return null; //when there where not any files left return null
    }