if I have to write a `ByteBuffer` to file, what's the best way? Using `InputStream` like here: <http...

# getting-started

[elect]

if I have to write a ByteBuffer to file, what's the best way? Using InputStream like here: https://stackoverflow.com/questions/35528409/write-a-large-inputstream-to-file-in-kotlin?

[diesieben07]

Embrace `java.nio`:

fun Path.channel(vararg options: OpenOption): FileChannel = FileChannel.open(this, *options)

fun main(args: Array<String>) {
    val buf: ByteBuffer = TODO()
    val file = Paths.get("output")

    file.channel(StandardOpenOption.CREATE, StandardOpenOption.WRITE).use { channel ->
        while (buf.hasRemaining()) channel.write(buf)
    }
}

[elect]

why while (buf.hasRemaining()) and not simply channel.write(buf)?

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can it simply write an arbitrarly amount of bytes? Why?

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I'll never get these methods..

[diesieben07]

Yes, channel.write may write only a portion of the buffer as per the Javadocs.

[diesieben07]

If you feed it a large buffer, it will only write as much as it can efficiently write in one go.

[elect]

what does it mean?

[elect]

for which reason would it efficientely write only a portion?

[diesieben07]

Channel is a very generic interface. It might be a channel bound to a network socket, which only has a limited buffer. You can't just send out 500MB immediately, you have to wait for the network speed. So as long as the network buffer is full, it cannot write.

[elect]

ah, that makes sense, thanks

[elect]

hi, just a quick question, this is valid also for reading I guess

[elect]

val buffer = FileChannel.open(path, StandardOpenOption.READ).use { channel ->
            bufferBig(channel.size().i).also {
                while (channel.read(it) > 0) Unit
            }
        }

[elect]

read() returns the number of bytes read

[diesieben07]

Yes, but why also here?