How to convert byte[] to String in Java?

Question

There are some SO quetions but no helped me. I would like to convert byte[] from org.apache.commons.codec.digest.HmacUtils to String. This code produces some weird output:

final String value = "value";
final String key = "key";
byte[] bytes = HmacUtils.hmacSha1(key, value);
String s = new String(bytes);

What am I doing wrong?

• Elliott Frisch: Generally, you display sha1 hashes in hex. Commons Codec has a hex encoder.
• user2864740: Probably relevant, possibly duplicate: stackoverflow.com/questions/9655181/… The resulting 'random binary' of the hash function will otherwise not be a useful text/string value.

Answer 1

Try to use:

String st = HmacUtils.hmacSha1Hex(key, value);

Answer 2

For a more general solution, if you don't have HmacUtils available:

// Prepare a buffer for the string
StringBuilder builder = new StringBuilder(bytes.length*2);
// Iterate through all bytes in the array
for(byte b : bytes) {
 // Convert them into a hex string
 builder.append(String.format("%02x",b));
 // builder.append(String.format("%02x",b).toUpperCase()); // for upper case characters
}
// Done
String s = builder.toString();

To explain your problem: You are using a hash function. So a hash is usually an array of bytes which should look quite random.

If you use new String(bytes) you try to create a string from these bytes. But Java will try to convert the bytes to characters.

For example: The byte 65 (hex 0x41) becomes the letter 'A'. 66 (hex 0x42) the letter 'B' and so on. Some numbers can't be converted into readable characters. Thats why you see strange characters like '�'.

So new String(new byte[]{0x41, 0x42, 0x43}) will become 'ABC'.

You want something else: You want each byte converted into a 2 digit hex String (and append these strings).

Greetings!

Answer 3

First, the result of hmacSha1 would produce a digest, not not a clear String. Besides, you may have to specify an encoding format, for example

String s = new String(bytes, "US-ASCII");

or

String s = new String(bytes, "UTF-8");

• jnemecz: Well, still I am getting a weird output ("WD:L#P�F8�]d�f�/�3") that doesn't correspond to this testing application - freeformatter.com/hmac-generator.html.
• user2864740: @user1315357 The confusion is the problem/expected output is not clearly specified.

Answer 4

You may need to have an encoding format. Check out this link here.

UTF-8 byte[] to String