问题

object UUIDConversion {
    fun UUID.toByteArray(): ByteArray {
        val byteBuffer = ByteBuffer.wrap(ByteArray(16))
        byteBuffer.putLong(this.mostSignificantBits)
        byteBuffer.putLong(this.leastSignificantBits)
        return byteBuffer.array()
    }

    fun ByteArray.toUUID(): UUID {
        val byteBuffer = ByteBuffer.wrap(this)
        val mostSignificantBits = byteBuffer.long
        val leastSignificantBits = byteBuffer.long
        return UUID(mostSignificantBits, leastSignificantBits)
    }

    fun ArrayList<UUID>.toByteArray(): ByteArray {
        val byteBuffer = ByteBuffer.wrap(ByteArray(size * 16))
        for (uuid in this) {
            byteBuffer.putLong(uuid.mostSignificantBits)
            byteBuffer.putLong(uuid.leastSignificantBits)
        }
        return byteBuffer.array()
    }

    fun ByteArray.toUUIDList(): ArrayList<UUID> {
        val byteBuffer = ByteBuffer.wrap(this)
        val uuidList = ArrayList<UUID>()
        while (byteBuffer.hasRemaining()) {
            val mostSignificantBits = byteBuffer.long
            val leastSignificantBits = byteBuffer.long
            uuidList.add(UUID(mostSignificantBits, leastSignificantBits))
        }
        return uuidList
    }
}

With these additional functions, you can now convert an ArrayList<UUID> to a ByteArray and vice versa using the toByteArray() and toUUIDList() functions.

object UUIDConversion {
    fun UUID.toByteArray() : ByteArray {
        val byteBuffer = ByteBuffer.wrap(ByteArray(16))
        byteBuffer.putLong(this.mostSignificantBits)
        byteBuffer.putLong(this.leastSignificantBits)
        return byteBuffer.array()
    }
    fun ByteArray.toUUID() : UUID {
        val byteBuffer = ByteBuffer.wrap(this)
        val mostSignificantBits = byteBuffer.long
        val leastSignificantBits = byteBuffer.long
        return UUID(mostSignificantBits, leastSignificantBits)
    }
}

答案1

得分: 1

你可以只使用+运算符来连接独立的UUID字节数组，如下所示：

val allUUIDs : ByteArray = listOfUUID.fold(ByteArray(0)) { buffer, uuid -> buffer + uuid.toByteArray() }

然而，如果你有很长的链条要转换，也许性能会显著下降。相反，你可以创建专门的方法来从/写入字节缓冲区：

import java.nio.ByteBuffer
import java.util.*
import kotlin.RuntimeException

fun ByteBuffer.readUUIDs(nbUUIDs : Int = remaining()/16) : Sequence<UUID> {
    if (nbUUIDs <= 0) return emptySequence()
    val nbBytes = nbUUIDs * 16
    // 防御性复制 -> 结果序列与接收缓冲区独立
    val defCpy = ByteArray(nbBytes)
    // 切片(slice)是必需的，以保持源缓冲区不受影响
    slice().get(defCpy)
    val view = ByteBuffer.wrap(defCpy)
    return (1..nbUUIDs).asSequence()
        .map { UUID(view.long, view.long) }
}

fun List<UUID>?.write() : ByteBuffer? {
    if (this == null || isEmpty()) return null;
    val buffer = ByteBuffer.allocate(Math.multiplyExact(size, 16))
    forEach { uuid ->
        buffer.putLong(uuid.mostSignificantBits)
        buffer.putLong(uuid.leastSignificantBits)
    }
    buffer.rewind()
    return buffer
}

fun main() {
    val uuids = (0..3).asSequence().map { UUID.randomUUID() }.toList()
    val writtenUUIDs = uuids.write()
    val uuidSequence = writtenUUIDs ?.readUUIDs() ?: throw RuntimeException("Bug")

    // 请注意，现在我们可以对缓冲区进行任何操作，而不会影响序列
    writtenUUIDs.getLong()
    writtenUUIDs.putLong(-1)

    val readBack = uuidSequence?.toList()
    assert(uuids == readBack) { throw RuntimeException("Bug") }
    println(uuids)
    println(readBack)
}

val allUUIDs : ByteArray = listOfUUID.fold(ByteArray(0)) { buffer, uuid -> buffer + uuid.toByteArray() }

import java.nio.ByteBuffer
import java.util.*
import kotlin.RuntimeException

fun ByteBuffer.readUUIDs(nbUUIDs : Int = remaining()/16) : Sequence<UUID> {
    if (nbUUIDs <= 0) return emptySequence()
    val nbBytes = nbUUIDs * 16
    // Defensive copy -> resulting sequence becomes independant from receiver buffer
    val defCpy = ByteArray(nbBytes)
    // slice is required to left source buffer untouched
    slice().get(defCpy)
    val view = ByteBuffer.wrap(defCpy)
    return (1..nbUUIDs).asSequence()
        .map { UUID(view.long, view.long) }
}

fun List<UUID>?.write() : ByteBuffer? {
    if (this == null || isEmpty()) return null;
    val buffer = ByteBuffer.allocate(Math.multiplyExact(size, 16))
    forEach { uuid ->
        buffer.putLong(uuid.mostSignificantBits)
        buffer.putLong(uuid.leastSignificantBits)
    }
    buffer.rewind()
    return buffer
}

fun main() {
    val uuids = (0..3).asSequence().map { UUID.randomUUID() }.toList()
    val writtenUUIDs = uuids.write()
    val uuidSequence = writtenUUIDs ?.readUUIDs() ?: throw RuntimeException("Bug")

    // Note that now, we can do whatever we want with the buffer. The sequence is not impacted
    writtenUUIDs.getLong()
    writtenUUIDs.putLong(-1)

    val readBack = uuidSequence?.toList()
    assert(uuids == readBack) { throw RuntimeException("Bug") }
    println(uuids)
    println(readBack)
}