Download file from remote URL in Kotlin

This post will discuss how to download a file from a remote URL in Kotlin.

1. Using `FileChannel.transferFrom()` function

The FileChannel#transferFrom() function is used to transfer bytes into this channel’s file from a readable byte channel. It accepts three parameters – the source channel, the position within the file to begin the transfer, and the maximum number of bytes to be transferred.

Its usage is demonstrated below using the use() function, which takes care of closing the opened streams and channels.

import java.io.FileOutputStream

import java.net.URL

import java.nio.channels.Channels

fun downloadFile(url: URL, outputFileName: String) {

url.openStream().use {

Channels.newChannel(it).use { rbc ->

FileOutputStream(outputFileName).use { fos ->

fos.channel.transferFrom(rbc, 0, Long.MAX_VALUE)

}

fun main() {

// call `downloadFile()` function

}

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2. Using `Files.copy()` function

We can also use the Files.copy() function to copy all bytes from an input stream to a file. It takes the input stream to read from and the path to the file and optional params indicating how copying should be done.

import java.net.URL

import java.nio.file.Files

import java.nio.file.Paths

fun downloadFile(url: URL, fileName: String) {

url.openStream().use { Files.copy(it, Paths.get(fileName)) }

}

fun main() {

// call `downloadFile()` function

}

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3. Using `BufferedInputStream`

Finally, we can read the file from the input stream byte-by-byte and write the bytes to a file output stream. This would translate to a simple code below:

import java.io.BufferedInputStream

import java.io.FileOutputStream

import java.net.URL

fun downloadFile(url: URL, fileName: String) {

url.openStream().use { inp ->

BufferedInputStream(inp).use { bis ->

FileOutputStream(fileName).use { fos ->

val data = ByteArray(1024)

var count: Int

while (bis.read(data, 0, 1024).also { count = it } != -1) {

fos.write(data, 0, count)

}

fun main() {

// call `downloadFile()` function

}

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That’s all about downloading a file from a remote URL in Kotlin.

Download file from remote URL in Kotlin

1. Using FileChannel.transferFrom() function

2. Using Files.copy() function

3. Using BufferedInputStream

Share this:

1. Using `FileChannel.transferFrom()` function

2. Using `Files.copy()` function

3. Using `BufferedInputStream`