How to convert an Object into a byte array in Kotlin

Question

I have a Kotlin object that I need converted into a byte array (byte[]). I understand how to convert a String and a series of other kinds of variables into byte[], but I can't find anything on doing this with an object.

Here is what I've tried:

override fun activateQuestion(instructorUserName: String, host: String, port: Int, questionToActivate: MultipleChoiceQuestion) { val socket = DatagramSocket() //This is the problem -- `.toByteArray(...)` only works for Strings val questionToActivateAsByteArray = questionToActivate.toByteArray(Charsets.UTF_8) //send byte[] data val packet = DatagramPacket(questionToActivateAsByteArray, questionToActivateAsByteArray.size, InetAddress.getByName(host), port) socket.send(packet) }

I usually opt to use json when sending objects over the wire. It allows you to decode them in any language. I would use a Jackson ObjectMapper and convert your object to a string before sending it as bytes. — flakes
– flakes, Commented Apr 5, 2020 at 18:00

M.Ed · Accepted Answer · 2022-07-18 07:59:21Z

Easiest way I've found with Kotlinx's serialization:

Mark your data class with @Serializable (if this isn't working for you, add the necessary plugins and dependencies to your build.gradle files).

@Serializable data class User(val name: String, val age: Int)

Then when you create an instance of it, you convert it into a Json string into a byte array it via Json.encodeToString(yourInstance).toByteArray().

Example:

val user = User(Mohammed, 25) val userAsByteArray = Json.encodeToString(user).toByteArray()

Bruno Azevedo · Accepted Answer · 2020-08-04 02:13:02Z

You can convert to bytearray in the java style. Something like this: Java Serializable Object to Byte Array

edit: to make it easier, its utility functions will look like this:

import java.io.* @Suppress("UNCHECKED_CAST") fun <T : Serializable> fromByteArray(byteArray: ByteArray): T { val byteArrayInputStream = ByteArrayInputStream(byteArray) val objectInput: ObjectInput objectInput = ObjectInputStream(byteArrayInputStream) val result = objectInput.readObject() as T objectInput.close() byteArrayInputStream.close() return result } fun Serializable.toByteArray(): ByteArray { val byteArrayOutputStream = ByteArrayOutputStream() val objectOutputStream: ObjectOutputStream objectOutputStream = ObjectOutputStream(byteArrayOutputStream) objectOutputStream.writeObject(this) objectOutputStream.flush() val result = byteArrayOutputStream.toByteArray() byteArrayOutputStream.close() objectOutputStream.close() return result }

to use them is just to do something like:

val yourSerializableObject = YourSerializableObject(...) val objectInByteArrayFormat = yourSerializableObject.toByteArray() val convertedObject = fromByteArray<YourSerializableObject>(objectInByteArrayFormat)

Don't forget that your object and all its attributes must be serializable

Codemaker2015 · Accepted Answer · 2020-11-16 04:59:17Z

The following is an object serializable class which is helpful to convert the object to bytes array and vice versa in Kotlin.

public class ObjectSerializer { companion object { public fun serialize(obj: Any?) : String { if (obj == null) { return "" } var baos = ByteArrayOutputStream() var oos = ObjectOutputStream(baos) oos.writeObject(obj) oos.close() return encodeBytes(baos.toByteArray()) } public fun deserialize(str: String?) : Any? { if (str == null || str.length() == 0) { return null } var bais = ByteArrayInputStream(decodeBytes(str)) var ois = ObjectInputStream(bais) return ois.readObject() } private fun encodeBytes(bytes: ByteArray) : String { var buffer = StringBuffer() for (byte in bytes) { buffer.append(((byte.toInt() shr 4) and 0xF plus 'a').toChar()) buffer.append(((byte.toInt()) and 0xF plus 'a').toChar()) } return buffer.toString() } private fun decodeBytes(str: String) : ByteArray { var bytes = ByteArray(str.length() / 2) for (i in 0..(str.length() - 1)) { var c = str.charAt(i) bytes.set(i / 2, ((c minus 'a').toInt() shl 4).toByte()) c = str.charAt(i + 1) bytes.set(i / 2, (bytes.get(i / 2) + (c minus 'a')).toByte()) } return bytes } } }

Could you please also include the package import part? Some dependencies didn't work when I copy your code to my local IDE.

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