How to convert a byte array to a hex string in Java?

Question

I have a byte array filled with hex numbers and printing it the easy way is pretty pointless because there are many unprintable elements. What I need is the exact hexcode in

Answer 1

Can't find any solution on this page that doesn't

1. Use a loop
2. Use javax.xml.bind.DatatypeConverter which compiles fine but often throws java.lang.NoClassDefFoundError at runtime.

Here's a solution which doesn't have the flaws above(no promises mine doesn't have other flaws though)

import java.math.BigInteger;

import static java.lang.System.out;
public final class App2 {
    // | proposed solution.
    public static String encode(byte[] bytes) {          
        final int length = bytes.length;

        // | BigInteger constructor throws if it is given an empty array.
        if (length == 0) {
            return "00";
        }

        final int evenLength = (int)(2 * Math.ceil(length / 2.0));
        final String format = "%0" + evenLength + "x";         
        final String result = String.format (format, new BigInteger(bytes));

        return result;
    }

    public static void main(String[] args) throws Exception {
        // 00
        out.println(encode(new byte[] {})); 

        // 01
        out.println(encode(new byte[] {1})); 

        //203040
        out.println(encode(new byte[] {0x20, 0x30, 0x40})); 

        // 416c6c20796f75722062617365206172652062656c6f6e6720746f2075732e
        out.println(encode("All your base are belong to us.".getBytes()));
    }
}   

I couldn't get this under 62 opcodes, but if you can live without 0 padding in case the first byte is less than 0x10, then the following solution only uses 23 opcodes. Really shows how "easy to implement yourself" solutions like "pad with a zero if string length is odd" can get pretty expensive if a native implementation is not already available(or in this case, if BigInteger had an option to prefix with zeros in toString).

public static String encode(byte[] bytes) {          
    final int length = bytes.length;

    // | BigInteger constructor throws if it is given an empty array.
    if (length == 0) {
        return "00";
    }

    return new BigInteger(bytes).toString(16);
}