Converting a byte array into a hex string

user_539599 0
Viewed 31880

Surprisingly (to me), this code does not do what I want:

fun ByteArray.toHexString() : String {
    return this.joinToString("") { it.toString(16) }
}

Turns out Byte is signed, so you get negative hex representations for individual bytes, which leads to a completely bogus end result.

Also, Byte.toString won't pad leading zeroes, which you'd want here.

What is the simplest (no additional libraries, ideally no extensions) resp. most efficient fix?

kotlin hex byte arrays string
4 Answers

As I am on Kotlin 1.3 you may also be interested in the UByte soon (note that it's an experimental feature. See also Kotlin 1.3M1 and 1.3M2 announcement)

E.g.:

@ExperimentalUnsignedTypes // just to make it clear that the experimental unsigned types are used
fun ByteArray.toHexString() = asUByteArray().joinToString("") { it.toString(16).padStart(2, '0') }

The formatting option is probably the nicest other variant (but maybe not that easily readable... and I always forget how it works, so it is definitely not so easy to remember (for me :-)):

fun ByteArray.toHexString() = joinToString("") { "%02x".format(it) }
user_62028690

printf does what we want here:

fun ByteArray.toHexString() : String {
    return this.joinToString("") {
        java.lang.String.format("%02x", it)
    }
}
user_5395990

This question has been answered, but I did not like the formatting. Here is something that formats it into something more readable ... at least for me.

@JvmOverloads
fun ByteArray.toHexString(separator: CharSequence = " ",  prefix: CharSequence = "[",  postfix: CharSequence = "]") =
    this.joinToString(separator, prefix, postfix) {
        String.format("0x%02X", it)
    }

output:

[0x10 0x22]
user_3463090 
fun ByteArray.toHexString() = joinToString("") {
    Integer.toUnsignedString(java.lang.Byte.toUnsignedInt(it), 16).padStart(2, '0')
}

Fortunately, Java has toUnsignedString methods on Integer and Long. UNfortunately, these methods are only on Integer and Long, so you need to convert each byte first (using Byte#toUnsignedInt).

user_73667070
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