Get MD5 String from Message Digest

Question

I understand how it works but if I want to print out the MD5 as String how would I do that?

public static void getMD5(String fileName) throws Exception{
    InputStream input =  new FileInputStream(fileName);
    byte[] buffer = new byte[1024];

    MessageDigest hash = MessageDigest.getInstance("MD5");
    int read;
    do {
        read = input.read(buffer);
        if (read > 0) {
            hash.update(buffer, 0, read);
        }
    } while (read != -1);
    input.close();
}

Solution 1

Try this

StringBuffer hexString = new StringBuffer();
MessageDigest md = MessageDigest.getInstance("MD5");
byte[] hash = md.digest();

for (int i = 0; i < hash.length; i++) {
    if ((0xff & hash[i]) < 0x10) {
        hexString.append("0"
                + Integer.toHexString((0xFF & hash[i])));
    } else {
        hexString.append(Integer.toHexString(0xFF & hash[i]));
    }
}

Solution 2

You can get it writing less:

String hex = (new HexBinaryAdapter()).marshal(md5.digest(YOUR_STRING.getBytes()))

Solution 3

    String input = "168";
    MessageDigest md = MessageDigest.getInstance("MD5");
    byte[] md5sum = md.digest(input.getBytes());
    String output = String.format("%032X", new BigInteger(1, md5sum));

or

DatatypeConverter.printHexBinary( MessageDigest.getInstance("MD5").digest("a".getBytes("UTF-8")))

Solution 4

You can also use Apache Commons Codec library. This library includes methods public static String md5Hex(InputStream data) and public static String md5Hex(byte[] data) in the DigestUtils class. No need to invent this yourself ;)

Solution 5

First you need to get the byte[] output of the MessageDigest:

byte[] bytes = hash.digest();

You can't easily print this though (with e.g. new String(bytes)) because it's going to contain binary that won't have good output representations. You can convert it to hex for display like this however:

StringBuilder sb = new StringBuilder(2 * bytes.length);
for (byte b : bytes) {
    sb.append("0123456789ABCDEF".charAt((b & 0xF0) >> 4));
    sb.append("0123456789ABCDEF".charAt((b & 0x0F)));
}
String hex = sb.toString();

View more solutions

Comments

[Dan J]

Do you know if there are any performance considerations here? Assuming we reused a single HexBinaryAdapter, would this introduce any significant overheads compared to doing the bit operations ourselves? We need to use this code a lot as we use the MD5 for URLs as the key into our image cache.

[mpontes]

Java's source is public. :) HexBinaryAdapter.marshal() only calls DatatypeConverter.printHexBinary() (you can actually use that instead, if you want to avoid instantiating a HexBinaryAdapter), which in turn instantiates a singleton DatatypeConverterImpl the first time it's called. After that, it's just a straight call to DatatypeConverterImpl's printHexBinary. It uses a method pretty similar to WhiteFang34's answer.

[FanaticD]

Note also that StringBuilder can be now used instead of StringBuffer, cons and pros of each are discussed in this question: stackoverflow.com/questions/355089/…

[mech]

Welcome to Stack Overflow, @WillBerger ! While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value.

[user1133275]

DatatypeConverter is not in JDK9

[user1133275]

HexBinaryAdapter is not in JDK9

[stacker]

@user1133275 See stackoverflow.com/questions/43574426/…

[user1133275]

yah I was just looking at that temporary hack for a lib, but for this question answers that do not depend on deprecated code are better.

[harley]

BigInteger seems to have an issue when the leading hex digit is 0.

[Teddy]

Thanks for mentioning the actual problem, and what would come as a first thought in byte-string which is to just use the string constructor. Also, I'm surprised no one suggested Base64. How does Base64 compare to these HexToBinary answers.

[Teddy]

Found this: stackoverflow.com/a/3183880/1364747