EasyExcel源码理解
简单读取文件代码流程
以最基础的读Execl操作入手，即以下方法：
@Test
public void simpleRead() {
String fileName = TestFileUtil.getPath() + "demo" + File.separator + "demo.xlsx";
EasyExcel.read(fileName, DemoData.class, new PageReadListener<DemoData>(dataList -> {
for (DemoData demoData : dataList) {
log.info("读取到一条数据{}", JSON.toJSONString(demoData));
}
})).sheet().doRead();
}
方法的每步作用：
read()和sheet()方法目的是构建对象，封装属性；doRead()方法利用前文构建的对象去解析Excel文件数据，并且执行自定义的业务代码。
read()
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;
}
ExcelReaderBuilder建造者构建的对象为ReadWorkbook。read()方法封装了文件路径、行对象Class、自定义处理Excel数据方法。
sheet()
public ExcelReaderSheetBuilder sheet(Integer sheetNo, String sheetName) {
// 其中build()方法封装核心的组建
ExcelReaderSheetBuilder excelReaderSheetBuilder = new ExcelReaderSheetBuilder(build());
if (sheetNo != null) {
excelReaderSheetBuilder.sheetNo(sheetNo);
}
if (sheetName != null) {
excelReaderSheetBuilder.sheetName(sheetName);
}
return excelReaderSheetBuilder;
}
ExcelReaderSheetBuilder建造者构建对象ExcelReader，ExcelReader对象封装的重要对象为ExcelAnalyser。
public ExcelReader(ReadWorkbook readWorkbook) {
// 封装中枢实现类 --> 此对象目的: 封装核心部件，执行核心部件
excelAnalyser = new ExcelAnalyserImpl(readWorkbook);
}
ExcelReader职责是调用ExcelAnalyser读取Excel文件数据；处理过数据后释放ExcelAnalyser资源。具体在代码中表现如下。
doRead()
public void doRead() {
if (excelReader == null) {
throw new ExcelGenerateException("Must use 'EasyExcelFactory.read().sheet()' to call this method");
}
excelReader.read(build());
excelReader.finish();
}
关键方法是读取Excel表格，处理数据。即excelReader.read(build());
public ExcelReader read(List<ReadSheet> readSheetList) {
// 读取文件数据，并且执行自定义业务代码
excelAnalyser.analysis(readSheetList, Boolean.FALSE);
return this;
}
ExcelAnalyser实现类ExcelAnalyserImpl执行核心方法
public void analysis(List<ReadSheet> readSheetList, Boolean readAll) {
try {
if (!readAll && CollectionUtils.isEmpty(readSheetList)) {
throw new IllegalArgumentException("Specify at least one read sheet.");
}
analysisContext.readWorkbookHolder().setParameterSheetDataList(readSheetList);
analysisContext.readWorkbookHolder().setReadAll(readAll);
try {
// 调用执行器
excelReadExecutor.execute();
} catch (ExcelAnalysisStopException e) {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Custom stop!");
}
}
} catch (RuntimeException e) {
finish();
throw e;
} catch (Throwable e) {
finish();
throw new ExcelAnalysisException(e);
}
}
调用执行器：
- 解析文件数据，并将每行数据封装到map集合中；
- 每解析一行后，根据集合执行自定义代码。
方法中出现三类重要的对象：ExcelAnalyser、AnalysisContext、ExcelReadExecutor.
ExcelAnalyser
文件解析器-中枢dispatch.
ExcelReader构造方法中初始化excelAnalyser属性，具体实现为ExcelAnalyserImpl。而ExcelAnalyserImpl构造方法传参为readWorkbook其中封装了文件的关键信息，代码如下。
public ExcelAnalyserImpl(ReadWorkbook readWorkbook) {
try {
// 根据导入的excel类型选择适配的文件解析执行器
choiceExcelExecutor(readWorkbook);
} catch (RuntimeException e) {
finish();
throw e;
} catch (Throwable e) {
finish();
throw new ExcelAnalysisException(e);
}
}
选择合适的文件解析执行器，封装ExcelAnalyser中两个关键的属性：analysisContext、excelReadExecutor。
private void choiceExcelExecutor(ReadWorkbook readWorkbook) throws Exception {
//...
case XLSX:
// 创建上下文对象，其中设置事件(Listener)的触发统一入口`DefaultAnalysisEventProcessor` --> 此类目的： 管理整个执行流程中的可复用对象
XlsxReadContext xlsxReadContext = new DefaultXlsxReadContext(readWorkbook, ExcelTypeEnum.XLSX);
analysisContext = xlsxReadContext;
// 设置解析执行器的具体实现
excelReadExecutor = new XlsxSaxAnalyser(xlsxReadContext, null);
break;
//...
}
AnalysisContext
流程执行上下文，存储了流程执行中所有公共的复用对象。
上下文对象封装两个重要属性：readWorkbookHolder等Holder、用户自定义Listener的方法的执行器analysisEventProcessor
AnalysisContext作为上下文资源的管理者，具体的资源存储在各个Holder中。
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;
case CSV:
readWorkbookHolder = new CsvReadWorkbookHolder(readWorkbook);
break;
default:
break;
}
currentReadHolder = readWorkbookHolder;
// 事件的触发统一入口
analysisEventProcessor = new DefaultAnalysisEventProcessor();
if (log.isDebugEnabled()) {
log.debug("Initialization 'AnalysisContextImpl' complete");
}
}
excelReadExecutor
文件解析执行器，其中关键方法为execute()。对文件进行每行内容解析并封装为对象的集合、执行自定义代码。
public void execute() {
for (ReadSheet readSheet : sheetList) {
readSheet = SheetUtils.match(readSheet, xlsxReadContext);
if (readSheet != null) {
try {
xlsxReadContext.currentSheet(readSheet);
// 解析文件内容， `XlsxRowHandler`类作为中枢调度解析：行(row - `XlsxRowHandler`) -> 行的元素(cell - `CellTagHandler`)
parseXmlSource(sheetMap.get(readSheet.getSheetNo()), new XlsxRowHandler(xlsxReadContext));
// Read comments
readComments(readSheet);
} catch (ExcelAnalysisStopSheetException e) {
if (log.isDebugEnabled()) {
log.debug("Custom stop!", e);
}
}
// The last sheet is read
// 执行Listener接口的doAfterAllAnalysed()方法 `ReadListener.doAfterAllAnalysed()`
xlsxReadContext.analysisEventProcessor().endSheet(xlsxReadContext);
}
}
}
其中核心的文件解析方法为parseXmlSource()，XlsxRowHandler类作为中枢调度解析：行(row - XlsxRowHandler) -> 行的元素(cell - CellTagHandler)
两个类都继承了AbstractXlsxTagHandler抽象类，两个核心方法startElement()、endElement();
CellTagHandler：startElement(): 初始化数据存放集合，数据结构等、endElement(): 封装每个单元格数据到tempCellData.RowTagHandler:startElement(): 初始化数据存放集合，数据结构等、endElement： 每行单元格解析完成后，执行次方法，调度事件处理业务代码.
执行的先后顺序为
RowTagHandler#startElement()–>CellTagHandler#startElement()–>CellTagHandler#endElement()–>RowTagHandler#endElement()
这里我们只关注最后的一个方法RowTagHandler#endElement()，即每行处理后调用自定义方法处理数据。
@Override
public 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 empty
if (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()));
// 每行数据封装到cellDataMap中，调用事件入口触发器处理每行数据 ReadListener.invoke();
xlsxReadContext.analysisEventProcessor().endRow(xlsxReadContext);
xlsxReadSheetHolder.setColumnIndex(null);
xlsxReadSheetHolder.setCellMap(new LinkedHashMap<>());
}
PageReadListener
public class PageReadListener<T> implements ReadListener<T> {
/**
* Default single handle the amount of data
*/
public static int BATCH_COUNT = 100;
/**
* Temporary storage of data
*/
private List<T> cachedDataList = ListUtils.newArrayListWithExpectedSize(BATCH_COUNT);
/**
* consumer
*/
private final Consumer<List<T>> consumer;
/**
* Single handle the amount of data
*/
private final int batchCount;
public PageReadListener(Consumer<List<T>> consumer) {
this(consumer, BATCH_COUNT);
}
public PageReadListener(Consumer<List<T>> consumer, int batchCount) {
this.consumer = consumer;
this.batchCount = batchCount;
}
@Override
public void invoke(T data, AnalysisContext context) {
cachedDataList.add(data);
if (cachedDataList.size() >= batchCount) {
consumer.accept(cachedDataList);
cachedDataList = ListUtils.newArrayListWithExpectedSize(batchCount);
}
}
@Override
public void doAfterAllAnalysed(AnalysisContext context) {
if (CollectionUtils.isNotEmpty(cachedDataList)) {
consumer.accept(cachedDataList);
}
}
}
流程图解析
