Java中如何利用POI優(yōu)雅的導出Excel文件

  <dependency>
   <groupId>org.apache.poi</groupId>
   <artifactId>poi-ooxml</artifactId>
   <version>4.1.2</version>
  </dependency>

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ExcelHeader {

 /**
  * 表頭
  * @return
  */
 String value() default "";

 /**
  * 列索引
  * @return
  */
 int columnIndex() default 0;
}

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {

 @ExcelHeader(value = "賬號")
 private String username;

 @ExcelHeader(value = "密碼")
 private String password;

 @ExcelHeader(value = "生日")
 @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
 @DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
 private LocalDateTime birthday;

 // 該字段沒有添加注解, Excel不導出
 private Integer age;

 public User(String username, String password, LocalDateTime birthday) {
  this.username = username;
  this.password = password;
  this.birthday = birthday;
 }
}

@Slf4j
class IdcPoiApplicationTests {

 @Test
 void contextLoads() throws NoSuchFieldException, IllegalAccessException, IOException {
  // 創(chuàng)建模擬數(shù)據(jù)
  User user1 = new User("admin", "123456", LocalDateTime.now());
  User user2 = new User("test", "123456", LocalDateTime.now());
  List<User> users = Arrays.asList(user1, user2);

  // 文件路徑
  String basePath = "/Users/cuishiying/Documents/spring-cloud-learning/idc-poi/oss/";
  String fileName = new SimpleDateFormat("yyyyMMddHHmmss").format(new Date()).toString() +".xls";

  // 將Excel寫入文件
  HSSFWorkbook workbook = exportExcel(users, User.class);
  workbook.setSheetName(0,"sheetName");//設置sheet的Name

  // 無論是通過HttpServletResponse導出還是導出到本地磁盤,本質(zhì)都是IO操作，所以這里將IO操作提取到外層。
  workbook.write(new File(basePath + File.separator + fileName));
 }

 /**
  *
  * @param data 需要導出的數(shù)據(jù)
  * @param clz 數(shù)據(jù)對應的實體類
  * @param <T> 泛型
  * @return Excel文件
  * @throws NoSuchFieldException
  * @throws IllegalAccessException
  */
 public <T> HSSFWorkbook exportExcel(List<T> data, Class<T> clz) throws NoSuchFieldException, IllegalAccessException {

  Field[] fields = clz.getDeclaredFields();
  List<String> headers = new LinkedList<>();
  List<String> variables = new LinkedList<>();

  // 創(chuàng)建工作薄對象
  HSSFWorkbook workbook=new HSSFWorkbook();//這里也可以設置sheet的Name
  // 創(chuàng)建工作表對象
  HSSFSheet sheet = workbook.createSheet();
  // 創(chuàng)建表頭
  Row rowHeader = sheet.createRow(0);

  // 表頭處理
  for (int h = 0; h < fields.length; h++) {
   Field field = fields[h];
   if (field.isAnnotationPresent(ExcelHeader.class)) {
    // 表頭
    ExcelHeader annotation = field.getAnnotation(ExcelHeader.class);
    headers.add(annotation.value());
    rowHeader.createCell(h).setCellValue(annotation.value());

    // 字段
    variables.add(field.getName());
   }
  }

  // 數(shù)據(jù)處理
  for (int i = 0; i < data.size() ; i++) {

   //創(chuàng)建工作表的行(表頭占用1行, 這里從第二行開始)
   HSSFRow row = sheet.createRow(i + 1);
   // 獲取一行數(shù)據(jù)
   T t = data.get(i);
   Class<&#63;> aClass = t.getClass();
   // 填充列數(shù)據(jù)
   for (int j = 0; j < variables.size(); j++) {

    Field declaredField = aClass.getDeclaredField(variables.get(j));
    declaredField.setAccessible(true);

    String key = declaredField.getName();
    Object value = declaredField.get(t);

    row.createCell(j).setCellValue(value.toString());
   }
  }
  log.info("Excel文件創(chuàng)建成功");
  return workbook;
 }
}