content: package com.alibaba.excel.util;
  
  import java.util.HashMap;
  import java.util.Map;
  
  import com.alibaba.excel.metadata.data.ImageData.ImageType;
  
  /**
   * file type utils
   *
   * @author Jiaju Zhuang
   */
  public class FileTypeUtils {
  
      private static final char[] DIGITS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
          'f'};
      private static final int IMAGE_TYPE_MARK_LENGTH = 28;
  
      private static final Map<String, ImageType> FILE_TYPE_MAP;
  
      /**
       * Default image type
       */
      public static ImageType defaultImageType = ImageType.PICTURE_TYPE_PNG;
  
      static {
          FILE_TYPE_MAP = new HashMap<>();
          FILE_TYPE_MAP.put("ffd8ff", ImageType.PICTURE_TYPE_JPEG);
          FILE_TYPE_MAP.put("89504e47", ImageType.PICTURE_TYPE_PNG);
      }
  
      public static int getImageTypeFormat(byte[] image) {
          ImageType imageType = getImageType(image);
          if (imageType != null) {
              return imageType.getValue();
          }
          return defaultImageType.getValue();
      }
  
      public static ImageType getImageType(byte[] image) {
          if (image == null || image.length <= IMAGE_TYPE_MARK_LENGTH) {
              return null;
          }
          byte[] typeMarkByte = new byte[IMAGE_TYPE_MARK_LENGTH];
          System.arraycopy(image, 0, typeMarkByte, 0, IMAGE_TYPE_MARK_LENGTH);
          return FILE_TYPE_MAP.get(encodeHexStr(typeMarkByte));
      }
  
      private static String encodeHexStr(byte[] data) {
          final int len = data.length;
          final char[] out = new char[len << 1];
          // two characters from the hex value.
          for (int i = 0, j = 0; i < len; i++) {
              out[j++] = DIGITS[(0xF0 & data[i]) >>> 4];
              out[j++] = DIGITS[0x0F & data[i]];
          }
          return new String(out);
      }
  }
  