背景：在图片压缩中，根据文件头判断png和jpg文件进行了压缩，但是对apng文件，文件头的前14个字节都一样（89504E470D0A1A0A0000000D4948），导致对apng图片进行压缩，图片白了

解决方法：进一步根据acTL和IHDR判断文件是apng还是png，代码如下：

    private boolean isApng(File file) {byte[] buffer = new byte[8];try (FileInputStream inputStream = new FileInputStream(file)) {inputStream.read(buffer, 0, 8);while (true) {// Read the chunk lengthint length = readInt(inputStream);// Read the chunk typeinputStream.read(buffer, 0, 4);String chunkType = new String(buffer, 0, 4, "UTF-8");if (chunkType.equals("acTL") && length == 8) {return true;} else {// Skip the chunk data and CRCinputStream.skip(length + 4);}// Check for the end of the fileif (inputStream.available() == 0) {break;}}return false;} catch (IOException e) {return false;}}private int readInt(InputStream inputStream) throws IOException {byte[] buffer = new byte[4];inputStream.read(buffer, 0, 4);return ((buffer[0] & 0xFF) << 24) | ((buffer[1] & 0xFF) << 16) | ((buffer[2] & 0xFF) << 8) | (buffer[3] & 0xFF);}