自定义注解的使用

自定义注解

/*** 自定义注解*/
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FieldLabel {// 字段中文String label();// 字段顺序int order() default 0;// 分组标识String group() default "default";}

解析自定义注解：

 // 1、获取当前类中声明的所有字段 2、字段有FieldLabel注解 3、通过group过滤 4、通过order排序List<Field> sortedFields = Arrays.stream(vo.getClass().getDeclaredFields()).filter(f -> f.isAnnotationPresent(FieldLabel.class)).filter(f -> groups.length == 0 || Arrays.asList(groups).contains(f.getAnnotation(FieldLabel.class).group())).sorted(Comparator.comparingInt(f -> f.getAnnotation(FieldLabel.class).order())).collect(Collectors.toList());

应用1：获取excel表头

 // 构建固定列头List<List<String>> head = new ArrayList<>();for (Field field : sortedFields) {FieldLabel annotation = field.getAnnotation(FieldLabel.class);head.add(Collections.singletonList(annotation.label()));}

应用2：转换指定分组的字段，将VO转为 List<Map<String, String>>：

@Slf4j
public class EntityConverter {public static List<Map<String, String>> convertToJson(Object obj, String... groups) {if (obj == null) {return Collections.emptyList();}List<Field> fields = Arrays.stream(obj.getClass().getDeclaredFields()).filter(f -> f.isAnnotationPresent(FieldLabel.class)).filter(f -> groups.length == 0 || Arrays.asList(groups).contains(f.getAnnotation(FieldLabel.class).group())).sorted(Comparator.comparingInt(f -> f.getAnnotation(FieldLabel.class).order())).collect(Collectors.toList());List<Map<String, String>> items = new ArrayList<>();for (Field field : fields) {try {// 允许通过反射访问私有(private)或其他受限成员field.setAccessible(true);FieldLabel annotation = field.getAnnotation(FieldLabel.class);Object value = field.get(obj);Map<String, String> item = new LinkedHashMap<>();item.put("label", annotation.label());item.put("value", value != null ? value.toString() : "");items.add(item);} catch (IllegalAccessException e) {log.error("字段转换出错，字段：{}，错误：{}", field.getName(), e.getMessage(), e);throw exception(ProjectErrorCode.ENTITY_CONVERTER_ERROR, e.getMessage());}}return items;}}