Image :: read size of JPG/PNG/BMP/GIF

If you would believe Google, everybody is searching for code that reads the dimensions of an image,without loading all those colorful pixels. Oh well, without further ado....

public class ImageUtil
{
   public static Dimension getImageDimension(File file) throws IOException
   {
      return ImageUtil.getImageDimension(new FileInputStream(file));
   }

   public static Dimension getImageDimension(InputStream in) throws IOException
   {
      DataInputStream dis = new DataInputStream(in);

      try
      {
         int header = dis.readUnsignedShort();

         if (header == 0x8950)
         {
            // PNG
            dis.readFully(new byte[(8 - 2) + 4 + 4]); // thanks Abuse

            return new Dimension(dis.readInt(), dis.readInt());
         }

         if (header == 0xffd8)
         {
            // JPG (see below)
         }
         else if (header == 0x424D)
         {
            // BMP
            dis.readFully(new byte[16]);

            int w = dis.read() | (dis.read() << 8) | (dis.read() << 16) | (dis.read() << 24);
            int h = dis.read() | (dis.read() << 8) | (dis.read() << 16) | (dis.read() << 24);
            return new Dimension(w, h);
         }
         else if (header == (('G' << 8) | ('I' << 0))) // GIF
         {
            // GIF
            dis.readFully(new byte[4]);
            int w = dis.read() | (dis.read() << 8);
            int h = dis.read() | (dis.read() << 8);
            return new Dimension(w, h);
         }
         else
         {
            throw new IllegalStateException("unexpected header: " + Integer.toHexString(header));
         }

         while (true) // JPG is not so straight forward
         {
            int marker = dis.readUnsignedShort();

            switch (marker)
            {
               case 0xffd8: // SOI
               case 0xffd0: // RST0
               case 0xffd1: // RST1
               case 0xffd2: // RST2
               case 0xffd3: // RST3
               case 0xffd4: // RST4
               case 0xffd5: // RST5
               case 0xffd6: // RST6
               case 0xffd7: // RST7
               case 0xffd9: // EOI
                  break;

               case 0xffdd: // DRI
                  dis.readUnsignedShort();
                  break;

               case 0xffe0: // APP0
               case 0xffe1: // APP1
               case 0xffe2: // APP2
               case 0xffe3: // APP3
               case 0xffe4: // APP4
               case 0xffe5: // APP5
               case 0xffe6: // APP6
               case 0xffe7: // APP7
               case 0xffe8: // APP8
               case 0xffe9: // APP9
               case 0xffea: // APPa
               case 0xffeb: // APPb
               case 0xffec: // APPc
               case 0xffed: // APPd
               case 0xffee: // APPe
               case 0xffef: // APPf
               case 0xfffe: // COM
               case 0xffdb: // DQT
               case 0xffc4: // DHT
               case 0xffda: // SOS
                  dis.readFully(new byte[dis.readUnsignedShort() - 2]);
                  break;

               case 0xffc0: // SOF0
               case 0xffc2: // SOF2
                  dis.readUnsignedShort();
                  dis.readByte();
                  int height = dis.readUnsignedShort();
                  int width = dis.readUnsignedShort();
                  return new Dimension(width, height);

               default:
                  throw new IllegalStateException("invalid jpg marker: " + Integer.toHexString(marker));
            }
         }
      }
      finally
      {
         dis.close();
      }
   }
}