BeanUtils(对象拷贝)

Beanutils

 /**
   * <pre>
   *     List<UserBean> userBeans = userDao.queryUsers();
   *     List<UserDTO> userDTOs = BeanUtil.batchTransform(UserDTO.class, userBeans);
   * </pre>
   *
   */
  public static <T> List<T> batchTransform(final Class<T> clazz, List<? extends Object> srcList) {
    if (CollectionUtils.isEmpty(srcList)) {
      return Collections.emptyList();
    }

    List<T> result = new ArrayList<>(srcList.size());
    for (Object srcObject : srcList) {
      result.add(transfrom(clazz, srcObject));
    }
    return result;
  }

  /**
   * 封装{@link org.springframework.beans.BeanUtils#copyProperties}，惯用与直接将转换结果返回
   *
   * <pre>
   *      UserBean userBean = new UserBean("username");
   *      return BeanUtil.transform(UserDTO.class, userBean);
   * </pre>
   */
  public static <T> T transfrom(Class<T> clazz, Object src) {
    if (src == null) {
      return null;
    }
    T instance = null;
    try {
      instance = clazz.newInstance();
    } catch (Exception e) {
      throw new BeanUtilsException(e);
    }
    org.springframework.beans.BeanUtils.copyProperties(src, instance, getNullPropertyNames(src));
    return instance;
  }

  private static String[] getNullPropertyNames(Object source) {
    final BeanWrapper src = new BeanWrapperImpl(source);
    PropertyDescriptor[] pds = src.getPropertyDescriptors();

    Set<String> emptyNames = new HashSet<String>();
    for (PropertyDescriptor pd : pds) {
      Object srcValue = src.getPropertyValue(pd.getName());
      if (srcValue == null) emptyNames.add(pd.getName());
    }
    String[] result = new String[emptyNames.size()];
    return emptyNames.toArray(result);
  }
/**
   * 根据列表里面的属性聚合
   *
   * <pre>
   *       List<ShopDTO> shopList = shopService.queryShops();
   *       Map<Integer, List<ShopDTO>> city2Shops = BeanUtil.aggByKeyToList("cityId", shopList);
   * </pre>
   */
  @SuppressWarnings("unchecked")
  public static <K, V> Map<K, List<V>> aggByKeyToList(String key, List<? extends Object> list) {
    Map<K, List<V>> map = new HashMap<K, List<V>>();
    if (CollectionUtils.isEmpty(list)) {// 防止外面传入空list
      return map;
    }
    try {
      Class<? extends Object> clazz = list.get(0).getClass();
      Field field = deepFindField(clazz, key);
      if (field == null) throw new IllegalArgumentException("Could not find the key");
      field.setAccessible(true);
      for (Object o : list) {
        K k = (K) field.get(o);
        if (map.get(k) == null) {
          map.put(k, new ArrayList<V>());
        }
        map.get(k).add((V) o);
      }
    } catch (Exception e) {
      throw new BeanUtilsException(e);
    }
    return map;
  }

  /**
   * 用于将一个对象的列表转换为列表中对象的属性集合
   *
   * <pre>
   *     List<UserDTO> userList = userService.queryUsers();
   *     Set<Integer> userIds = BeanUtil.toPropertySet("userId", userList);
   * </pre>
   */
  @SuppressWarnings("unchecked")
  public static <K> Set<K> toPropertySet(String key, List<? extends Object> list) {
    Set<K> set = new HashSet<K>();
    if (CollectionUtils.isEmpty(list)) {// 防止外面传入空list
      return set;
    }
    try {
      Class<? extends Object> clazz = list.get(0).getClass();
      Field field = deepFindField(clazz, key);
      if (field == null) throw new IllegalArgumentException("Could not find the key");
      field.setAccessible(true);
      for (Object o : list) {
        set.add((K)field.get(o));
      }
    } catch (Exception e) {
      throw new BeanUtilsException(e);
    }
    return set;
  }


  private static Field deepFindField(Class<? extends Object> clazz, String key) {
    Field field = null;
    while (!clazz.getName().equals(Object.class.getName())) {
      try {
        field = clazz.getDeclaredField(key);
        if (field != null) {
          break;
        }
      } catch (Exception e) {
        clazz = clazz.getSuperclass();
      }
    }
    return field;
  }