easyexcel流式导出

EasyExcel 支持流式导出，这是它的一个重要特性。流式导出可以有效解决大数据量导出时的内存溢出问题。

流式导出的优势

1. 内存友好 ：不会一次性将所有数据加载到内存中
2. 适合大数据量 ：可以处理百万级甚至更多的数据
3. 性能稳定 ：内存占用相对固定，不会随数据量增长而线性增加

基本用法示例

1. 简单流式导出

@GetMapping("/export")
public void export(HttpServletResponse response) throws IOException {
    // 设置响应头
    response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    response.setCharacterEncoding("utf-8");
    response.setHeader("Content-disposition", "attachment;filename=data.xlsx");
    
    // 创建ExcelWriter对象
    ExcelWriter excelWriter = EasyExcel.write(response.getOutputStream(), DemoData.class).build();
    
    // 分页查询数据并写入
    int pageSize = 1000;
    int pageNum = 1;
    
    while (true) {
        List<DemoData> dataList = getDataFromDatabase(pageNum, pageSize);
        if (dataList.isEmpty()) {
            break;
        }
        
        // 写入当前页数据
        WriteSheet writeSheet = EasyExcel.writerSheet("Sheet1")
                .build();
        excelWriter.write(dataList, writeSheet);
        
        pageNum++;
    }
    
    // 关闭流
    excelWriter.finish();
}

2. 使用分页助手

@GetMapping("/exportWithPage")
public void exportWithPage(HttpServletResponse response) throws IOException {
    response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    response.setCharacterEncoding("utf-8");
    response.setHeader("Content-disposition", "attachment;filename=data.xlsx");
    
    EasyExcel.write(response.getOutputStream(), DemoData.class)
            .sheet("Sheet1")
            .doWrite(() -> {
                // 分页查询数据
                List<DemoData> dataList = new ArrayList<>();
                int pageSize = 1000;
                int pageNum = 1;
                
                while (true) {
                    List<DemoData> pageData = getDataFromDatabase(pageNum, pageSize);
                    if (pageData.isEmpty()) {
                        break;
                    }
                    dataList.addAll(pageData);
                    pageNum++;
                }
                
                return dataList;
            });
}

3. 手动控制写入过程

@GetMapping("/exportManual")
public void exportManual(HttpServletResponse response) throws IOException {
    response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    response.setCharacterEncoding("utf-8");
    response.setHeader("Content-disposition", "attachment;filename=data.xlsx");
    
    ExcelWriter excelWriter = null;
    try {
        excelWriter = EasyExcel.write(response.getOutputStream(), DemoData.class).build();
        WriteSheet writeSheet = EasyExcel.writerSheet("Sheet1").build();
        
        // 分批写入数据
        int pageSize = 1000;
        int pageNum = 1;
        
        while (true) {
            List<DemoData> dataList = getDataFromDatabase(pageNum, pageSize);
            if (dataList.isEmpty()) {
                break;
            }
            
            excelWriter.write(dataList, writeSheet);
            pageNum++;
        }
    } finally {
        if (excelWriter != null) {
            excelWriter.finish();
        }
    }
}

4. 多Sheet流式导出

@GetMapping("/exportMultiSheet")
public void exportMultiSheet(HttpServletResponse response) throws IOException {
    response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    response.setCharacterEncoding("utf-8");
    response.setHeader("Content-disposition", "attachment;filename=data.xlsx");
    
    ExcelWriter excelWriter = EasyExcel.write(response.getOutputStream(), DemoData.class).build();
    
    try {
        // 第一个Sheet
        WriteSheet sheet1 = EasyExcel.writerSheet(0, "Sheet1").build();
        List<DemoData> data1 = getDataForSheet1();
        excelWriter.write(data1, sheet1);
        
        // 第二个Sheet
        WriteSheet sheet2 = EasyExcel.writerSheet(1, "Sheet2").build();
        List<DemoData> data2 = getDataForSheet2();
        excelWriter.write(data2, sheet2);
        
    } finally {
        excelWriter.finish();
    }
}

注意事项

1. 及时关闭资源 ：使用完后要调用 excelWriter.finish() 关闭流
2. 异常处理 ：要做好异常处理，确保资源能够正确释放
3. 数据分页 ：合理设置分页大小，一般建议1000-5000条数据为一批
4. 内存监控 ：虽然流式导出内存友好，但仍需监控JVM内存使用情况

流式导出是EasyExcel处理大数据量导出的最佳实践，特别适合需要导出大量数据的业务场景。