EasyExcel的源码流程（导入Excel）

1. 入口

2.  EasyExcel类继承了EasyExcelFactory类，EasyExcel自动拥有EasyExcelFactory父类的所有方法，如read()，readSheet()，write()，writerSheet()等等。

3. 进入.read()方法，需要传入三个参数(文件路径，表头映射类，read监听器)
   首先调用new ExcelReaderBuilder()方法，初始化ReadWorkbook对象
   设置完readWorkbook属性后调，返回excelReaderBuilder对象 

4. 这里又个传入的参数是read监听器，进入其内部看一下，我们自定义了PersonListener实现了ReadListener。ReadListener接口源码 ：

自定义的PersonListener类：

import com.alibaba.excel.context.AnalysisContext;
import com.alibaba.excel.event.AnalysisEventListener;
import com.aliyun.odps.jdbc.utils.LoggerFactory;
import org.springframework.stereotype.Component;import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.logging.Logger;@Component
public class PersonListener extends AnalysisEventListener<PersonTest> {//一行一行读出excel内容  不读表头  EasyExcel之所以效率高，也是因它一行一行读取，解析。@Overridepublic void invoke(PersonTest personTest, AnalysisContext analysisContext) {System.out.println("***"+personTest);}//读取表头@Overridepublic void invokeHeadMap(Map<Integer, String> headMap, AnalysisContext context) {System.out.println("表头"+headMap);}//读取完执行的方法@Overridepublic void doAfterAllAnalysed(AnalysisContext analysisContext) {System.out.println("读取全部后执行");}
}

5. 接下来调用的是.sheet()方法，这里我们会传入sheetNo、sheetName参数，调用build()方法创建ExcelReader对象，传入ExcelReaderSheetBuilder构造方法中，最终创ExcelReaderSheetBuilder对象 

6. 进入build()方法，build()方法生成了ExcelReader对象，初始化ExcelAnalyser，并实例化ExcelAnalyser。

在实例化ExcelAnalyser时，choiceExcelExecutor()方法通过excel格式使用不同的执行器。
我们看XLSX中，初始化了XlsxReadContext上下文对象，给到analysisContext，又初始化了XlsxSaxAnalyser解析器对象 

public class ExcelAnalyserImpl implements ExcelAnalyser {private static final Logger LOGGER = LoggerFactory.getLogger(ExcelAnalyserImpl.class);private AnalysisContext analysisContext;private ExcelReadExecutor excelReadExecutor;/*** Prevent multiple shutdowns*/private boolean finished = false;public ExcelAnalyserImpl(ReadWorkbook readWorkbook) {try {choiceExcelExecutor(readWorkbook);} catch (RuntimeException e) {finish();throw e;} catch (Throwable e) {finish();throw new ExcelAnalysisException(e);}}private void choiceExcelExecutor(ReadWorkbook readWorkbook) throws Exception {ExcelTypeEnum excelType = ExcelTypeEnum.valueOf(readWorkbook);switch (excelType) {case XLS:POIFSFileSystem poifsFileSystem;if (readWorkbook.getFile() != null) {poifsFileSystem = new POIFSFileSystem(readWorkbook.getFile());} else {poifsFileSystem = new POIFSFileSystem(readWorkbook.getInputStream());}// So in encrypted excel, it looks like XLS but it's actually XLSXif (poifsFileSystem.getRoot().hasEntry(Decryptor.DEFAULT_POIFS_ENTRY)) {InputStream decryptedStream = null;try {decryptedStream = DocumentFactoryHelper.getDecryptedStream(poifsFileSystem.getRoot().getFileSystem(), readWorkbook.getPassword());XlsxReadContext xlsxReadContext = new DefaultXlsxReadContext(readWorkbook, ExcelTypeEnum.XLSX);analysisContext = xlsxReadContext;excelReadExecutor = new XlsxSaxAnalyser(xlsxReadContext, decryptedStream);return;} finally {IOUtils.closeQuietly(decryptedStream);// as we processed the full stream already, we can close the filesystem here// otherwise file handles are leakedpoifsFileSystem.close();}}if (readWorkbook.getPassword() != null) {Biff8EncryptionKey.setCurrentUserPassword(readWorkbook.getPassword());}XlsReadContext xlsReadContext = new DefaultXlsReadContext(readWorkbook, ExcelTypeEnum.XLS);xlsReadContext.xlsReadWorkbookHolder().setPoifsFileSystem(poifsFileSystem);analysisContext = xlsReadContext;excelReadExecutor = new XlsSaxAnalyser(xlsReadContext);break;case XLSX:XlsxReadContext xlsxReadContext = new DefaultXlsxReadContext(readWorkbook, ExcelTypeEnum.XLSX);analysisContext = xlsxReadContext;excelReadExecutor = new XlsxSaxAnalyser(xlsxReadContext, null);break;case CSV:CsvReadContext csvReadContext = new DefaultCsvReadContext(readWorkbook, ExcelTypeEnum.CSV);analysisContext = csvReadContext;excelReadExecutor = new CsvExcelReadExecutor(csvReadContext);break;default:break;}}
/*
----------------------------------------略---------------------------------------------
*/
}

7. XlsxSaxAnalyser详解

    7.1 进入new XlsxSaxAnalyser(xlsxReadContext, null)方法看一下,这里使用到SAX模式模式解析excel

public XlsxSaxAnalyser(XlsxReadContext xlsxReadContext, InputStream decryptedStream) throws Exception {this.xlsxReadContext = xlsxReadContext;// 初始化缓存（cache）XlsxReadWorkbookHolder xlsxReadWorkbookHolder = xlsxReadContext.xlsxReadWorkbookHolder();OPCPackage pkg = readOpcPackage(xlsxReadWorkbookHolder, decryptedStream);xlsxReadWorkbookHolder.setOpcPackage(pkg);// Read the Shared information StringsPackagePart sharedStringsTablePackagePart = pkg.getPart(SHARED_STRINGS_PART_NAME);if (sharedStringsTablePackagePart != null) {// 指定默认缓存defaultReadCache(xlsxReadWorkbookHolder, sharedStringsTablePackagePart);// 分析sharedStringsTable.xml，解析excel所有数据到readCacheanalysisSharedStringsTable(sharedStringsTablePackagePart.getInputStream(), xlsxReadWorkbookHolder);}XSSFReader xssfReader = new XSSFReader(pkg);analysisUse1904WindowDate(xssfReader, xlsxReadWorkbookHolder);// 设置样式表setStylesTable(xlsxReadWorkbookHolder, xssfReader);sheetList = new ArrayList<>();sheetMap = new HashMap<>();commentsTableMap = new HashMap<>();Map<Integer, PackageRelationshipCollection> packageRelationshipCollectionMap = MapUtils.newHashMap();xlsxReadWorkbookHolder.setPackageRelationshipCollectionMap(packageRelationshipCollectionMap);// 获取所有sheet页XSSFReader.SheetIterator ite = (XSSFReader.SheetIterator)xssfReader.getSheetsData();int index = 0;if (!ite.hasNext()) {throw new ExcelAnalysisException("Can not find any sheet!");}// 遍历sheet页while (ite.hasNext()) {InputStream inputStream = ite.next();// 保存所有sheet页sheetList.add(new ReadSheet(index, ite.getSheetName()));// 保存所有sheet页的输入流sheetMap.put(index, inputStream);if (xlsxReadContext.readWorkbookHolder().getExtraReadSet().contains(CellExtraTypeEnum.COMMENT)) {CommentsTable commentsTable = ite.getSheetComments();if (null != commentsTable) {commentsTableMap.put(index, commentsTable);}}if (xlsxReadContext.readWorkbookHolder().getExtraReadSet().contains(CellExtraTypeEnum.HYPERLINK)) {PackageRelationshipCollection packageRelationshipCollection = Optional.ofNullable(ite.getSheetPart()).map(packagePart -> {try {return packagePart.getRelationships();} catch (InvalidFormatException e) {log.warn("Reading the Relationship failed", e);return null;}}).orElse(null);if (packageRelationshipCollection != null) {packageRelationshipCollectionMap.put(index, packageRelationshipCollection);}}index++;}}

    7.2 进入analysisSharedStringsTable方法，可以看到创建了一个SharedStringsTableHandler处理器

    7.3 再进入parseXmlSource看到xmlReader.setContentHandler(handler)这一行代码，设置了SharedStringsTableHandler处理器

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);}try {saxFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);} catch (Throwable ignore) {}try {saxFactory.setFeature("http://xml.org/sax/features/external-general-entities", false);} catch (Throwable ignore) {}try {saxFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);} catch (Throwable ignore) {}SAXParser saxParser = saxFactory.newSAXParser();XMLReader xmlReader = saxParser.getXMLReader();xmlReader.setContentHandler(handler);xmlReader.parse(inputSource);inputStream.close();} catch (IOException | ParserConfigurationException | SAXException e) {throw new ExcelAnalysisException(e);} finally {if (inputStream != null) {try {inputStream.close();} catch (IOException e) {throw new ExcelAnalysisException("Can not close 'inputStream'!");}}}}

    7.4 我们将断点打在SharedStringsTableHandler里，发现下一步进入到这里面的startElement()    starteElement()后会调用endElement()

    7.5 反复调用，excel所有数据读取到readcache中

8. 调用.doRead()方法，开始SAX解析

    8.1 进入build()方法

    8.2 build()执行完后，执行read()方法，read()里还会进入一次read() 

9. 调用ExcelAnalyserImpl里的analysis()方法，设置sheetList，并调用执行器开始执行解析 

    9.1 调用的XlsxSaxAnalyser解析器execute()

 10. 进入parseXmlSource()方法，发现和之前的sax差不多，但只两次传入的handler类型不同，还是看一下传入的ContentHandler参数具体实现,进入XlsxRowHandler 内部

public class XlsxRowHandler extends DefaultHandler {private final XlsxReadContext xlsxReadContext;private static final Map<String, XlsxTagHandler> XLSX_CELL_HANDLER_MAP = new HashMap<String, XlsxTagHandler>(32);static {CellFormulaTagHandler cellFormulaTagHandler = new CellFormulaTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.CELL_FORMULA_TAG, cellFormulaTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_CELL_FORMULA_TAG, cellFormulaTagHandler);CellInlineStringValueTagHandler cellInlineStringValueTagHandler = new CellInlineStringValueTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.CELL_INLINE_STRING_VALUE_TAG, cellInlineStringValueTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_CELL_INLINE_STRING_VALUE_TAG, cellInlineStringValueTagHandler);CellTagHandler cellTagHandler = new CellTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.CELL_TAG, cellTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_CELL_TAG, cellTagHandler);CellValueTagHandler cellValueTagHandler = new CellValueTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.CELL_VALUE_TAG, cellValueTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_CELL_VALUE_TAG, cellValueTagHandler);CountTagHandler countTagHandler = new CountTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.DIMENSION_TAG, countTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_DIMENSION_TAG, countTagHandler);HyperlinkTagHandler hyperlinkTagHandler = new HyperlinkTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.HYPERLINK_TAG, hyperlinkTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_HYPERLINK_TAG, hyperlinkTagHandler);MergeCellTagHandler mergeCellTagHandler = new MergeCellTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.MERGE_CELL_TAG, mergeCellTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_MERGE_CELL_TAG, mergeCellTagHandler);RowTagHandler rowTagHandler = new RowTagHandler();XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.ROW_TAG, rowTagHandler);XLSX_CELL_HANDLER_MAP.put(ExcelXmlConstants.X_ROW_TAG, rowTagHandler);}public XlsxRowHandler(XlsxReadContext xlsxReadContext) {this.xlsxReadContext = xlsxReadContext;}@Overridepublic void startElement(String uri, String localName, String name, Attributes attributes) throws SAXException {XlsxTagHandler handler = XLSX_CELL_HANDLER_MAP.get(name);if (handler == null || !handler.support(xlsxReadContext)) {return;}xlsxReadContext.xlsxReadSheetHolder().getTagDeque().push(name);handler.startElement(xlsxReadContext, name, attributes);}@Overridepublic void characters(char[] ch, int start, int length) throws SAXException {String currentTag = xlsxReadContext.xlsxReadSheetHolder().getTagDeque().peek();if (currentTag == null) {return;}XlsxTagHandler handler = XLSX_CELL_HANDLER_MAP.get(currentTag);if (handler == null || !handler.support(xlsxReadContext)) {return;}handler.characters(xlsxReadContext, ch, start, length);}@Overridepublic void endElement(String uri, String localName, String name) throws SAXException {XlsxTagHandler handler = XLSX_CELL_HANDLER_MAP.get(name);if (handler == null || !handler.support(xlsxReadContext)) {return;}handler.endElement(xlsxReadContext, name);xlsxReadContext.xlsxReadSheetHolder().getTagDeque().pop();}}

    10.1 startElement()和endElement()都有多种实现

11. 进入用到的重要的几个类CellTagHandler、RowTagHandler

CellTagHandler: 读取cell的值，并放入tempCellData

public void startElement(XlsxReadContext xlsxReadContext, String name, Attributes attributes) {XlsxReadSheetHolder xlsxReadSheetHolder = xlsxReadContext.xlsxReadSheetHolder();xlsxReadSheetHolder.setColumnIndex(PositionUtils.getCol(attributes.getValue(ExcelXmlConstants.ATTRIBUTE_R),xlsxReadSheetHolder.getColumnIndex()));// t="s" ,it means String// t="str" ,it means String,but does not need to be read in the 'sharedStrings.xml'// t="inlineStr" ,it means String,but does not need to be read in the 'sharedStrings.xml'// t="b" ,it means Boolean// t="e" ,it means Error// t="n" ,it means Number// t is null ,it means Empty or NumberCellDataTypeEnum type = CellDataTypeEnum.buildFromCellType(attributes.getValue(ExcelXmlConstants.ATTRIBUTE_T));xlsxReadSheetHolder.setTempCellData(new ReadCellData<>(type));xlsxReadSheetHolder.setTempData(new StringBuilder());// Put in data transformation informationString dateFormatIndex = attributes.getValue(ExcelXmlConstants.ATTRIBUTE_S);int dateFormatIndexInteger;if (StringUtils.isEmpty(dateFormatIndex)) {dateFormatIndexInteger = DEFAULT_FORMAT_INDEX;} else {dateFormatIndexInteger = Integer.parseInt(dateFormatIndex);}xlsxReadSheetHolder.getTempCellData().setDataFormatData(xlsxReadContext.xlsxReadWorkbookHolder().dataFormatData(dateFormatIndexInteger));}@Overridepublic void endElement(XlsxReadContext xlsxReadContext, String name) {XlsxReadSheetHolder xlsxReadSheetHolder = xlsxReadContext.xlsxReadSheetHolder();ReadCellData<?> tempCellData = xlsxReadSheetHolder.getTempCellData();StringBuilder tempData = xlsxReadSheetHolder.getTempData();String tempDataString = tempData.toString();CellDataTypeEnum oldType = tempCellData.getType();switch (oldType) {case STRING:// In some cases, although cell type is a string, it may be an empty tagif (StringUtils.isEmpty(tempDataString)) {break;}String stringValue = xlsxReadContext.readWorkbookHolder().getReadCache().get(Integer.valueOf(tempDataString));tempCellData.setStringValue(stringValue);break;case DIRECT_STRING:case ERROR:tempCellData.setStringValue(tempDataString);tempCellData.setType(CellDataTypeEnum.STRING);break;case BOOLEAN:if (StringUtils.isEmpty(tempDataString)) {tempCellData.setType(CellDataTypeEnum.EMPTY);break;}tempCellData.setBooleanValue(BooleanUtils.valueOf(tempData.toString()));break;case NUMBER:case EMPTY:if (StringUtils.isEmpty(tempDataString)) {tempCellData.setType(CellDataTypeEnum.EMPTY);break;}tempCellData.setType(CellDataTypeEnum.NUMBER);tempCellData.setNumberValue(BigDecimal.valueOf(Double.parseDouble(tempDataString)));break;default:throw new IllegalStateException("Cannot set values now");}if (tempCellData.getStringValue() != null&& xlsxReadContext.currentReadHolder().globalConfiguration().getAutoTrim()) {tempCellData.setStringValue(tempCellData.getStringValue().trim());}tempCellData.checkEmpty();tempCellData.setRowIndex(xlsxReadSheetHolder.getRowIndex());tempCellData.setColumnIndex(xlsxReadSheetHolder.getColumnIndex());xlsxReadSheetHolder.getCellMap().put(xlsxReadSheetHolder.getColumnIndex(), tempCellData);}

RowTagHandler: 当一行读取完毕后，调用分析事件处理器，处理一行数据

                            xlsxReadContext.analysisEventProcessor().endRow(xlsxReadContext);

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);}@Overridepublic void endElement(XlsxReadContext xlsxReadContext, String name) {XlsxReadSheetHolder xlsxReadSheetHolder = xlsxReadContext.xlsxReadSheetHolder();RowTypeEnum rowType = MapUtils.isEmpty(xlsxReadSheetHolder.getCellMap()) ? RowTypeEnum.EMPTY : RowTypeEnum.DATA;// It's possible that all of the cells in the row are emptyif (rowType == RowTypeEnum.DATA) {boolean hasData = false;for (Cell cell : xlsxReadSheetHolder.getCellMap().values()) {if (!(cell instanceof ReadCellData)) {hasData = true;break;}ReadCellData<?> readCellData = (ReadCellData<?>)cell;if (readCellData.getType() != CellDataTypeEnum.EMPTY) {hasData = true;break;}}if (!hasData) {rowType = RowTypeEnum.EMPTY;}}xlsxReadContext.readRowHolder(new ReadRowHolder(xlsxReadSheetHolder.getRowIndex(), rowType,xlsxReadSheetHolder.getGlobalConfiguration(), xlsxReadSheetHolder.getCellMap()));xlsxReadContext.analysisEventProcessor().endRow(xlsxReadContext);xlsxReadSheetHolder.setColumnIndex(null);xlsxReadSheetHolder.setCellMap(new LinkedHashMap<>());}

12. 进入endRow()方法

      endRow()里通过getIgnoreEmptyRow()来判断是否忽略空行（true为忽略，默认为true）

     想要设置IgnoreEmptyRow为false，可以在最初使用EasyExcel时设置：

13. 进入dealData()方法

private void dealData(AnalysisContext analysisContext) {ReadRowHolder readRowHolder = analysisContext.readRowHolder();Map<Integer, ReadCellData<?>> 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();}}}

14. dealData()方法中的invoke方法会执行ModelBuildEventListener里的invoke()方法，在这里会进行单行数据到实体类的映射，buildStringList()真正执行映射

15. 退回XlsxSaxAnalyser的解析器execute()方法

      进入readComments()方法,读取额外信息（批注、超链接、合并单元格信息读取）

	private void readComments(ReadSheet readSheet) {if (!xlsxReadContext.readWorkbookHolder().getExtraReadSet().contains(CellExtraTypeEnum.COMMENT)) {return;}CommentsTable commentsTable = commentsTableMap.get(readSheet.getSheetNo());if (commentsTable == null) {return;}Iterator<CellAddress> cellAddresses = commentsTable.getCellAddresses();while (cellAddresses.hasNext()) {CellAddress cellAddress = cellAddresses.next();XSSFComment cellComment = commentsTable.findCellComment(cellAddress);CellExtra cellExtra = new CellExtra(CellExtraTypeEnum.COMMENT, cellComment.getString().toString(),cellAddress.getRow(), cellAddress.getColumn());xlsxReadContext.readSheetHolder().setCellExtra(cellExtra);xlsxReadContext.analysisEventProcessor().extra(xlsxReadContext);}}

16. 最后进入.endSheet(xlsxReadContext)方法

@Overridepublic void endSheet(AnalysisContext analysisContext) {// 这里会调用所有监听器中的doAfterAllAnalysed方法，执行最后的操作for (ReadListener readListener : analysisContext.currentReadHolder().readListenerList()) {readListener.doAfterAllAnalysed(analysisContext);}}

17. 在读取完毕之后，执行finish()方法，关闭所有流 

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