EasyExcel导出合并表头的Excel

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>easyexcel</artifactId>
    <version>2.2.7</version>
</dependency>

import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.date.DatePattern;
import cn.hutool.core.date.DateUtil;
import cn.hutool.core.util.CharsetUtil;
import cn.hutool.core.util.URLUtil;
import cn.hutool.http.ContentType;
import cn.hutool.http.Header;
import com.alibaba.excel.EasyExcel;
import com.alibaba.excel.EasyExcelFactory;
import com.alibaba.excel.ExcelWriter;
import com.alibaba.excel.support.ExcelTypeEnum;
import com.alibaba.excel.write.builder.ExcelWriterSheetBuilder;
import com.alibaba.excel.write.merge.OnceAbsoluteMergeStrategy;
import com.alibaba.excel.write.metadata.WriteSheet;
import com.google.common.collect.Maps;
import org.apache.poi.util.StringUtil;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;
import java.util.Map;

public class EasyExcelUtil {

    public static void export(HttpServletResponse response, List<List<String>> headList,
                              List<List<Object>> dataList, String filename) throws IOException {
        export(response, headList, dataList, filename, null);
    }

    public static void export(HttpServletResponse response, List<List<String>> headList,
                              List<List<Object>> dataList, String filename,
                              List<OnceAbsoluteMergeStrategy> strategyList) throws IOException {
        String fileName = new String((filename + DateUtil.format(DateUtil.date(), DatePattern.PURE_DATE_PATTERN))
                .getBytes(), CharsetUtil.CHARSET_UTF_8);
        ExcelTypeEnum excelType = ExcelTypeEnum.XLSX;
        ServletOutputStream out = response.getOutputStream();
        response.setContentType(ContentType.MULTIPART.getValue());
        response.setCharacterEncoding(CharsetUtil.UTF_8);
        response.setHeader(Header.CONTENT_DISPOSITION.getValue(),
                "attachment;filename=" + URLUtil.encode(fileName, StringUtil.UTF8) + excelType.getValue());
        ExcelWriter writer = EasyExcelFactory
                .write(out)
                .excelType(excelType)
                .head(headList)
                .build();
        Map<Integer, Integer> columnWidth = Maps.newHashMap();
        for (int i = 0; i < headList.size(); i++) {
            List<String> list = headList.get(i);
            columnWidth.put(i, list.get(list.size() - 1).length() * 1000);
        }
        ExcelWriterSheetBuilder writerSheetBuilder = EasyExcel.writerSheet(0);
        if (CollUtil.isNotEmpty(strategyList)) {
            strategyList.forEach(writerSheetBuilder::registerWriteHandler);
        }
        WriteSheet sheet = writerSheetBuilder.build();
        sheet.setColumnWidthMap(columnWidth);
        sheet.setSheetName(filename);
        writer.write(dataList, sheet);
        writer.finish();
        out.close();
    }
}

import com.alibaba.excel.write.merge.OnceAbsoluteMergeStrategy;
import com.ilubov.util.EasyExcelUtil;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@RequestMapping("/test")
@RestController
public class TestController {

    // 只合并表头
    @GetMapping("/export1")
    public void export1(HttpServletResponse response) throws IOException {
        List<List<String>> headList = Lists.newArrayList();
        List<List<Object>> dataList = Lists.newArrayList();
        String filename = "test";
        for (int j = 1; j < 5; j++) {
            List<Object> data = Lists.newArrayList();
            for (int i = 1; i < 10; i++) {
                if (j == 1) {
                    String h1, h2 = String.format("head%s", i);
                    if (i > 5) {
                        h1 = String.format("head%s", 2);
                    } else {
                        h1 = String.format("head%s", 1);
                    }
                    headList.add(ImmutableList.of(h1, h2));
                }
                data.add(i);
            }
            dataList.add(data);
        }
        EasyExcelUtil.export(response, headList, dataList, filename);
    }

    // 合并表头并合并第一列相同单元格
    @GetMapping("/export2")
    public void export2(HttpServletResponse response) throws IOException {
        List<List<String>> headList = Lists.newArrayList();
        List<List<Object>> dataList = Lists.newArrayList();
        String filename = "test";
        for (int j = 1; j < 8; j++) {
            List<Object> data = Lists.newArrayList();
            for (int i = 1; i < 10; i++) {
                if (j == 1) {
                    String h1, h2 = String.format("head%s", i);
                    if (i > 5) {
                        h1 = String.format("head%s", 2);
                    } else {
                        h1 = String.format("head%s", 1);
                    }
                    headList.add(ImmutableList.of(h1, h2));
                }
                if (i == 1) {
                    data.add(j < 3 ? "A" : j < 5 ? "B" : "C");
                } else {
                    data.add(i);
                }
            }
            dataList.add(data);
        }
        EasyExcelUtil.export(response, headList, dataList, filename, this.merge(dataList));
    }

    // 合并第一列相同单元格
    private List<OnceAbsoluteMergeStrategy> merge(List<List<Object>> dataList) {
        List<OnceAbsoluteMergeStrategy> strategyList = Lists.newArrayList();
        int start = 2, end = 1;
        Object index, base = dataList.get(0).get(0);
        for (List<Object> objects : dataList) {
            index = objects.get(0);
            if (base.equals(index)) {
                end++;
            } else {
                base = index;
                if (end > start) {
                    strategyList.add(new OnceAbsoluteMergeStrategy(start, end, 0, 0));
                }
                start = end++ + 1;
            }
        }
        if (end > start) {
            strategyList.add(new OnceAbsoluteMergeStrategy(start, end, 0, 0));
        }
        return strategyList;
    }
}