Best way to translate this java code into kotlin

Question

URL url = new URL(urlSpec);
HttpURLConnection connection = (HttpURLConnection)url.openConnection();
InputStream in = connection.getInputStream();
int bytesRead = 0;
         


        

Answer 1

Instead of translating the code literally, make use of Kotlin's stdlib which offers a number of useful extension functions. Here's one version

val text = URL(urlSpec).openConnection().inputStream.bufferedReader().use { it.readText() }

To answer the original question: You're right, assignments are not treated as expressions. Therefore you will need to separate the assignment and the comparison. Take a look at the implementation in the stdlib for an example:

public fun Reader.copyTo(out: Writer, bufferSize: Int = DEFAULT_BUFFER_SIZE): Long {
    var charsCopied: Long = 0
    val buffer = CharArray(bufferSize)
    var chars = read(buffer)
    while (chars >= 0) {
        out.write(buffer, 0, chars)
        charsCopied += chars
        chars = read(buffer)
    }
    return charsCopied
}

Source: https://github.com/JetBrains/kotlin/blob/a66fc9043437d2e75f04feadcfc63c61b04bd196/libraries/stdlib/src/kotlin/io/ReadWrite.kt#L114

Answer 2

You could use apply block to execute the assignment:

val input= connection.getInputStream();
var bytesRead = 0;
val buffer = ByteArray(1024)
while (input.read(buffer).apply { bytesRead = this } > 0) {
    out.write(buffer, 0, bytesRead);
}

Answer 3

You could use something like this

This operation may be little heavy as a function is created each iteration.

val url = URL("urlSpec")
val connection = url.openConnection() as HttpURLConnection
val `in` = connection.inputStream
val buffer = ByteArray(1024)
var bytesRead: Int? = null
while ({ bytesRead = `in`.read(buffer); bytesRead }() != null) {
        out.write(buffer, 0, bytesRead!!)
}
out.close()