easyexcel是对poi基于事件机制解析excel文件的封装，poi又对sax解析xml文件进行了封装，所以要理解easyexcel解析的过程，就要先从sax开始。
- sax解析xml文件
使用sax解析xml文件时只要注册ContentHandler就行，sax是按行解析的，解析时会调用ContentHandler接口的钩子函数。
java"> SAXParserFactory factory = SAXParserFactory.newInstance();SAXParser saxParser = factory.newSAXParser();XMLReader xmlReader = saxParser.getXMLReader();xmlReader.setContentHandler(new DefaultHandler(){@Overridepublic void startElement(String uri, String localName, String qName, Attributes attributes){log.info("startElement-->>uri:{},localName:{},qName:{}",uri, localName,qName);}@Overridepublic void endElement(String uri, String localName, String qName){log.info("endElement-->>uri:{},localName:{},qName:{}",uri, localName,qName);}@Overridepublic void characters(char[] ch, int start, int length){log.info("characters-->>ch:{}, start:{}, length:{}", new String(ch,start,length), start, length);}});InputStream inputStream = new FileInputStream(Var.xmlFile);xmlReader.parse(new InputSource(inputStream));inputStream.close();
java"> OPCPackage opcPackage = OPCPackage.open(Var.excelFile, PackageAccess.READ);XSSFReader reader = new XSSFReader(opcPackage);XMLReader xmlReader = XMLReaderFactory.createXMLReader();xmlReader.setContentHandler(new SheetHandler());Iterator<InputStream> sheetsData = reader.getSheetsData();while (sheetsData.hasNext()){InputStream next = sheetsData.next();InputSource inputSource = new InputSource(next);xmlReader.parse(inputSource);next.close();}
在poi解析大excel文件的基础上出现了easyexcel，先看下easyexcel的用法，真的很easy啊，调静态方法read，传文件路径就行，获取到每行数据时，会帮我们封装成实体类，我们在invoke中进行处理即可。
java">EasyExcel.read(Var.excelFile, WfqData.class,new AnalysisEventListener<WfqData>() {@Overridepublic void invoke(WfqData data, AnalysisContext analysisContext) {// 按行读文件}@Overridepublic void doAfterAllAnalysed(AnalysisContext analysisContext) {log.info("处理文件结束");}}).headRowNumber(2)// 表头第二行，第一行是免责申明.doReadAll();
接下来开始看easyexcel的源码。read()方法中会构造ReadWorkbook对象，然后设置excel文件的File对象，注册读监听器。
java"> public static ExcelReaderBuilder read(String pathName, Class head, ReadListener readListener) {ExcelReaderBuilder excelReaderBuilder = new ExcelReaderBuilder();excelReaderBuilder.file(pathName);if (head != null) {excelReaderBuilder.head(head);}if (readListener != null) {excelReaderBuilder.registerReadListener(readListener);}return excelReaderBuilder;}
然后构造ExcelReader对象用来读取excel文件。
java"> public void doReadAll() {ExcelReader excelReader = build();excelReader.readAll();excelReader.finish();}
接下来根据excel文件类型确定解析器，
java">private void choiceExcelExecutor(ReadWorkbook readWorkbook) throws Exception {ExcelTypeEnum excelType = ExcelTypeEnum.valueOf(readWorkbook);switch (excelType) {case XLS:......break;case XLSX:XlsxReadContext xlsxReadContext = new DefaultXlsxReadContext(readWorkbook, ExcelTypeEnum.XLSX);analysisContext = xlsxReadContext;excelReadExecutor = new XlsxSaxAnalyser(xlsxReadContext, null);break;default:break;}}
然后设置一堆的配置，在解析的时候会用到，这些配置都保存在DefaultXlsxReadContext中，使用默认的解析事件处理器DefaultAnalysisEventProcessor，在解析excel的过程中会通过这个事件处理器调用我们注册进来的监听器方法。
java"> public AnalysisContextImpl(ReadWorkbook readWorkbook, ExcelTypeEnum actualExcelType) {if (readWorkbook == null) {throw new IllegalArgumentException("Workbook argument cannot be null");}switch (actualExcelType) {case XLS:readWorkbookHolder = new XlsReadWorkbookHolder(readWorkbook);break;case XLSX:readWorkbookHolder = new XlsxReadWorkbookHolder(readWorkbook);break;default:break;}currentReadHolder = readWorkbookHolder;analysisEventProcessor = new DefaultAnalysisEventProcessor();if (LOGGER.isDebugEnabled()) {LOGGER.debug("Initialization 'AnalysisContextImpl' complete");}}
解析前最重要的一环就是打开excel文档OPCPackage.open(xlsxReadWorkbookHolder.getFile());，这里就是我们熟悉的poi解析excel文件做的事情，然后获取每个要解析的sheet页，使用ReadSheet包装。
java"> public XlsxSaxAnalyser(XlsxReadContext xlsxReadContext, InputStream decryptedStream) throws Exception {this.xlsxReadContext = xlsxReadContext;// Initialize cacheXlsxReadWorkbookHolder xlsxReadWorkbookHolder = xlsxReadContext.xlsxReadWorkbookHolder();OPCPackage pkg = readOpcPackage(xlsxReadWorkbookHolder, decryptedStream);xlsxReadWorkbookHolder.setOpcPackage(pkg);ArrayList<PackagePart> packageParts = pkg.getPartsByContentType(XSSFRelation.SHARED_STRINGS.getContentType());if (!CollectionUtils.isEmpty(packageParts)) {PackagePart sharedStringsTablePackagePart = packageParts.get(0);// Specify default cachedefaultReadCache(xlsxReadWorkbookHolder, sharedStringsTablePackagePart);// Analysis sharedStringsTable.xmlanalysisSharedStringsTable(sharedStringsTablePackagePart.getInputStream(), xlsxReadWorkbookHolder);}XSSFReader xssfReader = new XSSFReader(pkg);analysisUse1904WindowDate(xssfReader, xlsxReadWorkbookHolder);xlsxReadWorkbookHolder.setStylesTable(xssfReader.getStylesTable());sheetList = new ArrayList<ReadSheet>();sheetMap = new HashMap<Integer, InputStream>();commentsTableMap = new HashMap<Integer, CommentsTable>();XSSFReader.SheetIterator ite = (XSSFReader.SheetIterator)xssfReader.getSheetsData();int index = 0;if (!ite.hasNext()) {throw new ExcelAnalysisException("Can not find any sheet!");}while (ite.hasNext()) {InputStream inputStream = ite.next();sheetList.add(new ReadSheet(index, ite.getSheetName()));sheetMap.put(index, inputStream);if (xlsxReadContext.readWorkbookHolder().getExtraReadSet().contains(CellExtraTypeEnum.COMMENT)) {CommentsTable commentsTable = ite.getSheetComments();if (null != commentsTable) {commentsTableMap.put(index, commentsTable);}}index++;}}
解析是在XlsxSaxAnalyser#execute方法中进行的，依次遍历获取的每个sheet页，保存下来后进行解析，就是poi解析excel文件的过程了。
java"> public void execute() {for (ReadSheet readSheet : sheetList) {readSheet = SheetUtils.match(readSheet, xlsxReadContext);if (readSheet != null) {xlsxReadContext.currentSheet(readSheet);parseXmlSource(sheetMap.get(readSheet.getSheetNo()), new XlsxRowHandler(xlsxReadContext));// Read commentsreadComments(readSheet);// The last sheet is readxlsxReadContext.analysisEventProcessor().endSheet(xlsxReadContext);}}}private void parseXmlSource(InputStream inputStream, ContentHandler handler) {InputSource inputSource = new InputSource(inputStream);try {SAXParserFactory saxFactory;String xlsxSAXParserFactoryName = xlsxReadContext.xlsxReadWorkbookHolder().getSaxParserFactoryName();if (StringUtils.isEmpty(xlsxSAXParserFactoryName)) {saxFactory = SAXParserFactory.newInstance();} else {saxFactory = SAXParserFactory.newInstance(xlsxSAXParserFactoryName, null);}...SAXParser saxParser = saxFactory.newSAXParser();XMLReader xmlReader = saxParser.getXMLReader();xmlReader.setContentHandler(handler);xmlReader.parse(inputSource);inputStream.close();}}
每次解析时都会回调XlsxRowHandler中的startElement、characters、endElement方法。
RowTagHandler#startElement()方法中会先获取当前要解析的行，然后与之前解析到的行进行对比，防止遗漏。
java"> public void startElement(XlsxReadContext xlsxReadContext, String name, Attributes attributes) {XlsxReadSheetHolder xlsxReadSheetHolder = xlsxReadContext.xlsxReadSheetHolder();int rowIndex = PositionUtils.getRowByRowTagt(attributes.getValue(ExcelXmlConstants.ATTRIBUTE_R),xlsxReadSheetHolder.getRowIndex());Integer lastRowIndex = xlsxReadContext.readSheetHolder().getRowIndex();while (lastRowIndex + 1 < rowIndex) {xlsxReadContext.readRowHolder(new ReadRowHolder(lastRowIndex + 1, RowTypeEnum.EMPTY,xlsxReadSheetHolder.getGlobalConfiguration(), new LinkedHashMap<Integer, Cell>()));xlsxReadContext.analysisEventProcessor().endRow(xlsxReadContext);xlsxReadSheetHolder.setColumnIndex(null);xlsxReadSheetHolder.setCellMap(new LinkedHashMap<Integer, Cell>());lastRowIndex++;}xlsxReadSheetHolder.setRowIndex(rowIndex);}
解析完一行后，在AbstractCellValueTagHandler#endElement中会将当前行的列数和对应的值保存到cellMap(private Map<Integer, Cell> cellMap;)中。
java">public void endElement(XlsxReadContext xlsxReadContext, String name) {XlsxReadSheetHolder xlsxReadSheetHolder = xlsxReadContext.xlsxReadSheetHolder();CellData tempCellData = xlsxReadSheetHolder.getTempCellData();StringBuilder tempData = xlsxReadSheetHolder.getTempData();CellDataTypeEnum oldType = tempCellData.getType();switch (oldType) {case DIRECT_STRING:case STRING:case ERROR:tempCellData.setStringValue(tempData.toString());break;case BOOLEAN:tempCellData.setBooleanValue(BooleanUtils.valueOf(tempData.toString()));break;case NUMBER:case EMPTY:tempCellData.setType(CellDataTypeEnum.NUMBER);tempCellData.setNumberValue(new BigDecimal(tempData.toString()));break;default:throw new IllegalStateException("Cannot set values now");}// set string valuesetStringValue(xlsxReadContext);if (tempCellData.getStringValue() != null&& xlsxReadContext.currentReadHolder().globalConfiguration().getAutoTrim()) {tempCellData.setStringValue(tempCellData.getStringValue());}tempCellData.checkEmpty();xlsxReadSheetHolder.getCellMap().put(xlsxReadSheetHolder.getColumnIndex(), tempCellData);}
然后在RowTagHandler#endElement中调用xlsxReadContext.analysisEventProcessor().endRow(xlsxReadContext);方法进行处理，这里会调用DefaultAnalysisEventProcessor#dealData处理每行的实际数据，其实就是调用读监听器的invoke方法，也就是我们在EasyExcel.read中传的第三个参数。
java"> private void dealData(AnalysisContext analysisContext) {ReadRowHolder readRowHolder = analysisContext.readRowHolder();Map<Integer, CellData> cellDataMap = (Map)readRowHolder.getCellMap();readRowHolder.setCurrentRowAnalysisResult(cellDataMap);int rowIndex = readRowHolder.getRowIndex();int currentHeadRowNumber = analysisContext.readSheetHolder().getHeadRowNumber();boolean isData = rowIndex >= currentHeadRowNumber;// Last head columnif (!isData && currentHeadRowNumber == rowIndex + 1) {buildHead(analysisContext, cellDataMap);}// Now is datafor (ReadListener readListener : analysisContext.currentReadHolder().readListenerList()) {try {if (isData) {readListener.invoke(readRowHolder.getCurrentRowAnalysisResult(), analysisContext);} else {readListener.invokeHead(cellDataMap, analysisContext);}} catch (Exception e) {onException(analysisContext, e);break;}if (!readListener.hasNext(analysisContext)) {throw new ExcelAnalysisStopException();}}}
完成一个sheet页的解析，就会调用每个监听的doAfterAllAnalysed()方法。
java"> public void endSheet(AnalysisContext analysisContext) {for (ReadListener readListener : analysisContext.currentReadHolder().readListenerList()) {readListener.doAfterAllAnalysed(analysisContext);}}
至此完成了对excel文件的解析。
总结下，easyexcel解析excel文件，先初始化用来解析excel文件用到的参数，比如文件路径、表头行、行数据class等，然后使用poi基于事件的机制进行解析。获取到数据后会把列索引和cell数据保存到map，然后调用每个监听器的invoke方法进行处理。有不对的地方请大神指出，欢迎大家一起讨论交流，共同进步。
