webflux 导出excel

可以使用 Apache POI 库来实现在 Spring WebFlux 中导出 Excel 文件。下面是一个简单的示例代码：

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.server.reactive.ServerHttpResponse;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.io.IOException;
import java.io.OutputStream;
import java.util.List;

public class ExcelExporter {
    public static <T> Mono<Void> export(ServerHttpResponse response, List<T> data) {
        DataBufferFactory bufferFactory = response.bufferFactory();
        HttpHeaders headers = response.getHeaders();
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        headers.setContentDispositionFormData("attachment", "data.xlsx");

        SXSSFWorkbook workbook = new SXSSFWorkbook();
        Sheet sheet = workbook.createSheet("Data");
        Row header = sheet.createRow(0);
        // 设置表头
        // ...

        // 填充数据
        int rowIndex = 1;
        for (T item : data) {
            Row row = sheet.createRow(rowIndex++);
            // 设置每行单元格数据
            // ...
        }

        // 将数据写入响应流
        OutputStream outputStream;
        try {
            outputStream = response.getServletResponse().getOutputStream();
            workbook.write(outputStream);
            workbook.close();
        } catch (IOException e) {
            return Mono.error(e);
        }

        // 返回响应流
        Flux<DataBuffer> dataBufferFlux = Flux.create(dataBufferSink -> {
            DataBuffer dataBuffer = bufferFactory.allocateBuffer();
            try {
                outputStream.flush();
                outputStream.close();
                dataBufferSink.next(dataBuffer);
                dataBufferSink.complete();
            } catch (IOException e) {
                dataBufferSink.error(e);
            }
        });
        return response.writeWith(dataBufferFlux);
    }
}

调用示例：

public Mono<Void> exportData(ServerHttpResponse response) {
    List<Data> data = // 获取数据列表
    return ExcelExporter.export(response, data);
}

这个示例代码适用于导出数据量不大的情况。如果数据量很大，可以使用 SXSSFWorkbook 来提高生成 Excel 文件的性能。