@ExcelProperty 使用占位符，实现动态表头效果

@ExcelProperty 使用占位符，实现动态表头效果

easyexcel 想实现动态表头，根据官方文档，采用以下方式：

private List<List<String>> head() {
        List<List<String>> list = new ArrayList<List<String>>();
        List<String> head0 = new ArrayList<String>();
        head0.add("字符串" + System.currentTimeMillis());
        List<String> head1 = new ArrayList<String>();
        head1.add("数字" + System.currentTimeMillis());
        List<String> head2 = new ArrayList<String>();
        head2.add("日期" + System.currentTimeMillis());
        list.add(head0);
        list.add(head1);
        list.add(head2);
        return list;
    }

个人感觉该方式不够灵活，且实体类中定义的样式也失效了，如果表格字段较多，需要写一大堆List。经过研究，通过另一种方式实现动态表头效果。

定义导出实体类，此处省略get、set方法

public class UserModel {

    @ExcelProperty(value = {"${title}", "姓名"})
    private String name;

    @ExcelProperty(value = {"${title}", "生日"})
    @DateTimeFormat(value = "yyyy-MM-dd")
    private Date birth;

    @ExcelProperty(value = {"${title}", "年龄"})
    private int age;
}

${title}表示需要设置的标题

自定义CustomerTitleHandler

自定义CustomerTitleHandler，实现CellWriteHandler接口，重写beforeCellCreate方法，使用PropertyPlaceholderHelper 类将实体类中的占位符替换为真实的title

public class CustomerTitleHandler implements CellWriteHandler {
    private String title;
    PropertyPlaceholderHelper placeholderHelper = new PropertyPlaceholderHelper("${", "}");
    public CustomerTitleHandler(String title) {
        this.title = title;
    }
    @Override
    public void beforeCellCreate(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder,Row row, Head head, Integer integer, Integer integer1, Boolean aBoolean) {
        if (head=null) {
            List<String> headNameList = head.getHeadNameList();
            if (CollectionUtils.isNotEmpty(headNameList)) {
                Properties properties = new Properties();
                properties.setProperty("title", title);
                headNameList.set(0, placeholderHelper.replacePlaceholders(headNameList.get(0), properties));
            }
        }
    }
    @Override
    public void afterCellCreate(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder,
                                Cell cell, Head head, Integer integer, Boolean aBoolean) {

    }
    @Override
    public void afterCellDataConverted(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder,
                                       CellData cellData, Cell cell, Head head, Integer integer, Boolean aBoolean) {

    }
    @Override
    public void afterCellDispose(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder,
                                 List<CellData> list, Cell cell, Head head, Integer integer, Boolean aBoolean) {

    }
}

创建ExcelWriter，生成excel文件

public class EasyExcelTest {
    public static void main(String[] args) {
        File file = new File("C:\Users\ambit\Desktop\user.xlsx");
         String title = "用户信息112233";
        ExcelWriter excelWriter = null;
        try {
            excelWriter = EasyExcel.write(file, UserModel.class).excelType(ExcelTypeEnum.XLSX).build();
            WriteSheet sheet = EasyExcel.writerSheet().registerWriteHandler(new CustomerTitleHandler(title)).build();
            List<UserModel> list;
            for (int i = 0; i < 5; i++) {
                list = new ArrayList<>(1);
                UserModel userModel = new UserModel();
                userModel.setName("张三" + i);
                userModel.setBirth(new Date());
                userModel.setAge(18 + i);
                list.add(userModel);
                excelWriter.write(list, sheet);
            }
        } finally {
            if (excelWriter != null) {
                excelWriter.finish();
            }
        }
    }
}

最终效果如下：