java to determine whether the file is an image file

  public static final HashMap map = new HashMap();

    static {
        map.put("89504E47", "png");
        map.put("49492A00", "tif");
        map.put("FFD8FF", "jpg");
    }

    public static String getFileType(String filePath) {
        return (String) map.get(getFileHeader(filePath));
    }


    public static String getFileHeader(String filePath) {
        FileInputStream is = null;
        String value = null;
        try {
            is = new FileInputStream(filePath);
            byte[] b = new byte[4];
            /*
             * int read() Reads a byte of data from this input stream. int read(byte[] b) will read at most b.length from this input stream
             * bytes of data are read into a byte array. int read(byte[] b, int off, int len)
             * Read up to len bytes of data from this input stream into a byte array.
             */
            is.read(b, 0, b.length);
            value = bytesToHexString(b);
        } catch (Exception e) {
        } finally {
            if (null != is) {
                try {
                    is.close();
                } catch (IOException e) {
                }
            }
        }
        return value;
    }

    private static String bytesToHexString(byte[] src) {
        StringBuilder builder = new StringBuilder();
        if (src == null || src.length <= 0) {
            return null;
        }
        String hv;
        for (int i = 0; i < src.length; i++) {
            // Returns the string representation of an integer argument as a hexadecimal (base 16) unsigned integer, converted to uppercase
            hv = Integer.toHexString(src[i] & 0xFF).toUpperCase();
            if (hv.length() < 2) {
                builder.append(0);
            }
            builder.append(hv);
        }
        // System.out.println(builder.toString()+"4");
        return builder.toString();
    }

    /**
     * ############################################################################
     */

    public static String getImageType(File srcFilePath) {
        FileInputStream imgFile;
        byte[] b = new byte[10];
        int l = -1;
        try {
            imgFile = new FileInputStream(srcFilePath);
            l = imgFile.read(b);
            imgFile.close();
        } catch (Exception e) {
            return null;
        }
        if (l == 10) {
            byte b0 = b[0];
            byte b1 = b[1];
            byte b2 = b[2];
            byte b3 = b[3];
            byte b6 = b[6];
            byte b7 = b[7];
            byte b8 = b[8];
            byte b9 = b[9];
            for (int i = 0; i < 10; i++) {
                System.out.println(b[i]);
            }
            if (b0 == (byte) 'G' && b1 == (byte) 'I' && b2 == (byte) 'F') {
                return "gif";
            } else if (b1 == (byte) 'P' && b2 == (byte) 'N' && b3 == (byte) 'G') {
                return "png";
            } else if (b6 == (byte) 'J' && b7 == (byte) 'F' && b8 == (byte) 'I' && b9 == (byte) 'F') {
                return "jpg";
            } else {
                return null;
            }
        } else {
            return null;
        }
    }


    public static void main(String[] args) {
        File file = new File("D:/home/ubuntu/BoneAgeDemo/CT/JPG/20171229100855.jpg");
        getFileType("D:/home/ubuntu/BoneAgeDemo/CT/JPG/f-d-5-2-20.tif");
        getImageType(file);
    }

    getImageType measured the tif file, the ASCII code is 73 73 42 0 8 0 0 0 13 0, it has not been verified, and the second is to read the length and width of the image, which is basically the case