动态表头导出EasyExcel

在 Spring Boot 中结合 EasyExcel 实现动态表头导出（无实体类，表头和字段（前端传表名，字段值动态查询，返回List<Map<String,Object>>）由前端传递）可以通过以下步骤实现。以下是完整示例：

1. 前端请求数据结构

假设前端传递的 JSON 格式如下：

{
  "headers": [
    {"title": "姓名", "field": "name"},
    {"title": "年龄", "field": "age"},
    {"title": "城市", "field": "city"}
  ],
  "data": [
    {"name": "张三", "age": 25, "city": "北京"},
    {"name": "李四", "age": 30, "city": "上海"}
  ]
}

2. 后端 DTO 定义

定义接收参数的 DTO 类：

@Data
public class ExportRequest {
    private List<Header> headers;
    private List<Map<String, Object>> data;

    @Data
    public static class Header {
        private String title;  // 表头名称
        private String field;  // 数据字段名
    }
}

3. Controller 层接口

处理导出请求：

@RestController
public class ExportController {

    @Autowired
    private ExportService exportService;

    @PostMapping("/export")
    public void exportExcel(@RequestBody ExportRequest request, HttpServletResponse response) {
        exportService.export(request, response);
    }
}

4. Service 层实现

核心导出逻辑：

@Service
public class ExportService {

    public void export(ExportRequest request, HttpServletResponse response) {
        try {
            // 设置响应头
            response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
            response.setCharacterEncoding("UTF-8");
            String fileName = URLEncoder.encode("动态导出.xlsx", "UTF-8");
            response.setHeader("Content-Disposition", "attachment; filename=" + fileName);

            // 获取输出流
            OutputStream outputStream = response.getOutputStream();

            // 动态构建表头和数据
            WriteSheet writeSheet = EasyExcel.writerSheet("Sheet1").build();
            ExcelWriter excelWriter = EasyExcel.write(outputStream).build();

            // 动态添加表头
            WriteTable writeTable = new WriteTable();
            List<List<String>> head = buildHead(request.getHeaders());
            writeTable.setHead(head);

            // 动态填充数据
            List<List<Object>> data = buildData(request.getHeaders(), request.getData());
            excelWriter.write(data, writeSheet, writeTable);

            // 关闭流
            excelWriter.finish();
            outputStream.flush();
        } catch (IOException e) {
            throw new RuntimeException("导出失败", e);
        }
    }

    // 构建表头
    private List<List<String>> buildHead(List<ExportRequest.Header> headers) {
        List<List<String>> head = new ArrayList<>();
        for (ExportRequest.Header header : headers) {
            List<String> columnHead = Collections.singletonList(header.getTitle());
            head.add(columnHead);
        }
        return head;
    }

    // 构建数据行
    private List<List<Object>> buildData(List<ExportRequest.Header> headers, List<Map<String, Object>> dataList) {
        List<List<Object>> data = new ArrayList<>();
        for (Map<String, Object> rowData : dataList) {
            List<Object> row = new ArrayList<>();
            for (ExportRequest.Header header : headers) {
                row.add(rowData.get(header.getField()));
            }
            data.add(row);
        }
        return data;
    }
}

5. 关键点说明

动态表头
- 通过 buildHead() 方法将前端传递的 headers 转换为 EasyExcel 需要的 List<List<String>> 格式。
动态数据
- 通过 buildData() 方法，根据 headers 中定义的 field 字段顺序，从 data 中提取对应值，构建数据行。
流式导出
- 使用 ExcelWriter 直接操作输出流，避免内存溢出（适合大数据量）。

6. 测试与验证

使用 Postman 发送请求：

URL: POST http://localhost:8080/export

Body（JSON）：

{
  "headers": [
    {"title": "姓名", "field": "name"},
    {"title": "年龄", "field": "age"},
    {"title": "城市", "field": "city"}
  ],
  "data": [
    {"name": "张三", "age": 25, "city": "北京"},
    {"name": "李四", "age": 30, "city": "上海"}
  ]
}