引入依赖

		<dependency>
			<groupId>com.alibaba</groupId>
			<artifactId>easyexcel</artifactId>
			<version>4.0.1</version>
		</dependency>

动态合并单元格

		List<List<String>> head = new ArrayList<>();
        head.add(List.of("date"));
        head.add(List.of("system"));
        head.add(List.of("metric"));
        head.add(List.of("value"));
        List<Obj> list = new ArrayList<>();
        list.add(new Obj( "2023-01-01", "system1", "metric","value"));
        list.add(new Obj( "2023-01-01", "system1", "metric1","value1"));
        list.add(new Obj( "2023-01-01", "system1", "metric2","value2"));
        list.add(new Obj( "2023-01-01", "system1", "metric3","value3"));
        list.add(new Obj( "2023-01-01", "system2", "metric4","value4"));
        list.add(new Obj( "2023-01-01", "system2", "metric5","value5"));
        list.add(new Obj( "2023-01-01", "system2", "metric6","value6"));
        list.add(new Obj( "2023-01-01", "system2", "metric7","value7"));

        String fileName = "template.xls";
        File file = new File(fileName);
        // 内容的策略(设置合并单元格居中)
        WriteCellStyle contentWriteCellStyle = new WriteCellStyle();
        contentWriteCellStyle.setHorizontalAlignment(HorizontalAlignment.CENTER);
        contentWriteCellStyle.setVerticalAlignment(VerticalAlignment.CENTER);
        HorizontalCellStyleStrategy horizontalCellStyleStrategy = new HorizontalCellStyleStrategy(new WriteCellStyle(),contentWriteCellStyle);

        LoopMergeStrategy loopMergeStrategy = new LoopMergeStrategy(list.size(),0);
        LoopMergeStrategy loopMergeStrategy1 = new LoopMergeStrategy(4,1);
        EasyExcel.write(file)
                .head(head)
                .sheet()
                // 开启相等值 行合并,从行索引1(excel中第二行)开始合并, 指定跨行合并的列索引
                .registerWriteHandler(loopMergeStrategy)
                .registerWriteHandler(loopMergeStrategy1)
                .registerWriteHandler(horizontalCellStyleStrategy)
                .doWrite(list);

        System.out.println("导出成功");

    }
    @Data
    @AllArgsConstructor
    static class Obj{
        private String date;
        private String system;
        private String metric;
        private String value;
    }