@Excel注解将字段转换并且忽略大小写

在Java中，使用注解可以很方便地实现字段转换和忽略大小写的功能。具体实现如下：

1. 定义注解类ExcelField，用于标记需要转换的字段。

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ExcelField {
    String value() default "";
}

2. 在需要转换的字段上添加ExcelField注解，并指定转换后的字段名。

public class User {
    @ExcelField("用户名")
    private String username;
    @ExcelField("邮箱")
    private String email;
    //...
}

3. 定义一个工具类ExcelUtil，用于读取Excel文件并转换成对象列表。

public class ExcelUtil {
    public static <T> List<T> readExcel(String filePath, Class<T> clazz) throws Exception {
        List<T> list = new ArrayList<>();
        Workbook workbook = WorkbookFactory.create(new File(filePath));
        Sheet sheet = workbook.getSheetAt(0);
        List<String> headers = getHeader(sheet.getRow(0));
        for (int i = 1; i <= sheet.getLastRowNum(); i++) {
            Row row = sheet.getRow(i);
            T obj = clazz.newInstance();
            for (int j = 0; j < headers.size(); j++) {
                String header = headers.get(j);
                Cell cell = row.getCell(j);
                Field field = getField(clazz, header);
                if (field != null && cell != null) {
                    field.setAccessible(true);
                    field.set(obj, convertValue(field.getType(), cell.getStringCellValue()));
                }
            }
            list.add(obj);
        }
        return list;
    }

    private static List<String> getHeader(Row row) {
        List<String> headers = new ArrayList<>();
        for (int i = 0; i < row.getLastCellNum(); i++) {
            Cell cell = row.getCell(i);
            if (cell != null) {
                headers.add(cell.getStringCellValue());
            }
        }
        return headers;
    }

    private static Field getField(Class<?> clazz, String header) {
        for (Field field : clazz.getDeclaredFields()) {
            if (field.isAnnotationPresent(ExcelField.class)) {
                ExcelField excelField = field.getAnnotation(ExcelField.class);
                if (excelField.value().equalsIgnoreCase(header)) {
                    return field;
                }
            } else if (field.getName().equalsIgnoreCase(header)) {
                return field;
            }
        }
        return null;
    }

    private static Object convertValue(Class<?> clazz, String value) {
        if (clazz == String.class) {
            return value;
        } else if (clazz == int.class || clazz == Integer.class) {
            return Integer.parseInt(value);
        } else if (clazz == double.class || clazz == Double.class) {
            return Double.parseDouble(value);
        } else {
            return value;
        }
    }
}

4. 使用ExcelUtil读取Excel文件并转换成对象列表。

public static void main(String[] args) throws Exception {
    List<User> users = ExcelUtil.readExcel("user.xlsx", User.class);
    for (User user : users) {
        System.out.println(user.getUsername() + "," + user.getEmail());
    }
}

这样就可以实现对Excel文件中的字段进行转换，并且忽略大小写了。