URL编码的Kotlin语言实现如下：

private val base16EncodeTable = "0123456789ABCDEF"

fun urlEncode(data: ByteArray): String {
    if (data.isEmpty()) {
        return ""
    }
    val result = StringBuilder()
    for (i in data.indices) {
        val intValue = data[i].toInt()
        when (intValue) {
            //man ascii看ASCII编码对应表
            //字符   十进制
            //'0' => 48   |   '9' => 57
            //'a' => 97   |   'z' => 122
            //'A' => 65   |   'Z' => 90
            //'-' => 45   |   '_' => 95
            //'*' => 42   |   '.' => 46
            //' ' => 32
            in 48..57, in 65..90, in 97..122 -> result.append(intValue.toChar())
            45, 95, 46, 42 -> result.append(intValue.toChar())
            32 -> result.append('+')
            else -> {
                //向右移动4bit，获得高4bit
                val highByte = intValue shr 4 and 0x0F
                //与0x0F做位与运算，获得低4bit
                val lowByte = intValue and 0x0F
                result.append('%')
                result.append(base16EncodeTable[highByte])
                result.append(base16EncodeTable[lowByte])
            }
        }
    }
    return result.toString()
}

此算法的结果与java.net.URLEncoder的编码结果完全一样。

URL解码的Kotlin语言实现如下：

//把16进制字符转换成10进制表示的数字
private fun hex2dec(c: Char): Int {
    return when (c) {
        in '0'..'9' -> c - '0'
        in 'a'..'f' -> c - 'a' + 10
        in 'A'..'F' -> c - 'A' + 10
        else -> 0
    }
}

fun urlDecode(input: String): ByteArray {
    val inputLength = input.length

    if (inputLength == 0) {
        return ByteArray(0)
    }

    val output = ByteArray(inputLength)
    var outputLength = 0
    var i = 0
    while (i < inputLength) {
        val c = input[i]
        if (c == '%') {
            val x = input[++i]
            val y = input[++i]
            //16进制数字转换为10进制数字的过程
            output[outputLength++] = (hex2dec(x) * 16 + hex2dec(y)).toByte()
        } else if (c == '+') {
            output[outputLength++] = ' '.toByte()
        } else {
            output[outputLength++] = c.toByte()
        }
        i++
    }
    val outputCopy = ByteArray(outputLength)
    System.arraycopy(output, 0, outputCopy, 0, outputLength)
    return outputCopy
}