How to convert an image from URL to hex string?

Question

I am downloading an image from URL as follows:

BufferedImage image = null;
URL url = new URL("http://www.ex.com/image/pic.jpg");
image = ImageIO.read(url);

I would like to convert it to something like the following hex string format:

89504E470D0A1A0A0000000D4948445200000124000001150802000000C6BD0FB3000000017352474200AECE1CE9000000097048597300000EC400000EC401952B0E1B000050B849444154785EED7D0B745CD759EE09E5618742A5C6F1833CB01A6E630587565E2154EE0D579203756DE823764B1ACAEB5A70EBAB2C08588EDB

But I don't know how to do that. How can I do that?

Answer 1

You could do a combination of the following:

1. Get byte array of image: Java- Convert bufferedimage to byte[] without writing to disk
2. Get hex string of byte array: How to convert a byte array to a hex string in Java?

Answer 2

To read a image into a byte array:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write( image, "jpg", baos );
baos.flush();
byte[] imageInByte = baos.toByteArray();
baos.close();

And to show it as String:

public static String bytesToHex(byte[] bytes) {
    final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
    char[] hexChars = new char[bytes.length * 2];
    int v;
    for ( int j = 0; j < bytes.length; j++ ) {
        v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return new String(hexChars);
}

Answer 3

Just get the image in byte[] flavor the usual Java I/O way and feed that in turn to DataTypeConverter#printHexBinary() to get a hex string out of it.

ByteArrayOutputStream output = new ByteArrayOutputStream();

try (InputStream input = new URL("http://example.com/some.jpg").openStream()) {
    byte[] buffer = new byte[10240];
    for (int length = 0; (length = input.read(buffer)) > 0;) {
         output.write(buffer, 0, length);
    }
}

String hex = DatatypeConverter.printHexBinary(output.toByteArray());
// ...

Note that you don't need the whole Java 2D API ( ImageIO et.al.) for this. This is only useful if you actually intend to manipulate the image (resize, crop, skew, etc).

Answer 4

In addition to the other answers, once you have read the image, you can also use the existing javax.xml.bind.DatatypeConverter class to convert the byte array to a hex string. Ideally use the approach from @BalusC to save memory and directly read the image into a byte array, and then simply do

String s = javax.xml.bind.DatatypeConverter.printHexBinary(byteArray);