Convert string unicode to UTF-8

convert.kt

import java.util.regex.Matcher
import java.util.regex.Pattern

fun String.unicode(): String {
    return unicodeToUtf8().unicodeToUtf8(16)
}

fun String.unicodeToUtf8(radix: Int = 10): String {
    val p = Pattern.compile(if (radix == 10) "&#(\\d+);|." else "&#x(.+?);|.")
    val sb = StringBuilder()
    val m: Matcher = p.matcher(this)
    while (m.find()) if (m.group(1) != null) {
        sb.append(m.group(1).toInt(radix).toChar())
    } else {
        sb.append(m.group(0) as String)
    }
    return sb.toString()
}