EasyExcel 多线程导出

### 如何使用 EasyExcel 实现多线程导出 Excel 文件 为了处理大数据量的报表导出并提高效率，可以采用多线程的方式进行数据导出。下面是一个具体的实现方案。 #### 创建自定义的数据读取器类 `DataReader` 此部分负责从数据库或其他源获取待导出的数据： ```java public class DemoDataReader implements DataReader<DemoData> { private List<DemoData> dataList; @Override public boolean hasNext() { return !dataList.isEmpty(); } @Override public DemoData next() throws Exception { if (hasNext()) { return dataList.remove(0); } throw new NoSuchElementException("No more elements"); } // 构造函数用于初始化数据列表 public DemoDataReader(List<DemoData> dataList) { this.dataList = dataList; } } ``` #### 定义数据模型类 `DemoData` 该实体类表示要被写入到 Excel 中的一条记录结构： ```java @Data class DemoData { String string; Integer integer; Date date; // Getters and Setters... } ``` #### 编写自定义的数据写出器类 `DataWriter` 此类实现了将每一条数据实际写入文件的功能： ```java public class DemoDataWriter extends AbstractExcelWriteHandler { @Override protected void invokeInternal(WriteSheetHolder writeSheetHolder, AnalysisContext context, WriteTableHolder writeTableHolder) { Sheet sheet = writeSheetHolder.getSheet(); // 可在此处设置样式等操作 super.invokeInternal(writeSheetHolder, context, writeTableHolder); } } ``` #### 多线程分页导出逻辑封装于 `ExcelExport` 类中 这个核心组件协调着整个过程中的并发控制与资源管理： ```java import com.alibaba.excel.write.handler.AbstractExcelWriteHandler; import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.Future; public class ExcelExport<T> { private final ThreadPoolTaskExecutor threadPool; private final int pageSize; private final DataReader<T> dataReader; private final DataWriter<T> dataWriter; public ExcelExport(DataReader<T> dataReader, DataWriter<T> dataWriter) { this(dataReader, dataWriter, Runtime.getRuntime().availableProcessors()); } public ExcelExport(DataReader<T> dataReader, DataWriter<T> dataWriter, int poolSize) { this.dataReader = dataReader; this.dataWriter = dataWriter; this.pageSize = 10_000; // 默认页面大小为一万条记录 this.threadPool = createThreadPool(poolSize); } /** * 开始执行多线程分页导出流程. */ public void export(int startPage, long totalRecords) throws InterruptedException, ExecutionException { int totalPages = calculateTotalPages(totalRecords); Future<?>[] futures = new Future[totalPages]; for (int i = 0; i < totalPages; ++i) { int currentPageIndex = i + startPage; Callable<Void> task = () -> processPage(currentPageIndex); futures[i] = threadPool.submit(task); } waitForAllTasksToComplete(futures); closeResources(); } private void processPage(int pageIndex) { try { List<T> pageItems = fetchPage(pageIndex); synchronized (dataWriter) { dataWriter.writeBatch(pageItems.toArray(new Object[0])); } } catch (Exception e) { System.err.println("Failed to process page " + pageIndex + ": " + e.getMessage()); } } private List<T> fetchPage(int pageIndex) throws Exception { List<T> result = new ArrayList<>(); for (int j = 0; j < pageSize && dataReader.hasNext(); ++j) { T item = dataReader.next(); result.add(item); } return result; } private static ThreadPoolTaskExecutor createThreadPool(int corePoolSize) { ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor(); executor.setCorePoolSize(corePoolSize); executor.setMaxPoolSize(Integer.MAX_VALUE); executor.initialize(); return executor; } private static int calculateTotalPages(long recordCount) { return Math.toIntExact((recordCount + PAGE_SIZE - 1L) / PAGE_SIZE); } private static void waitForAllTasksToComplete(Future<?>... tasks) throws InterruptedException, ExecutionException { for (Future<?> future : tasks) { future.get(); } } private void closeResources() { threadPool.shutdown(); } } ``` 通过上述代码片段展示了如何利用 Java 的多线程机制配合 EasyExcel 库来高效完成大量数据向 Excel 表格内的转换工作[^3]。