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How to integrate WebSocket with a backend server in Kotlin Android.

How to integrate WebSocket with a backend server in Kotlin Android..

Here's a step-by-step tutorial on integrating WebSocket with a backend server in Kotlin Android:

Step 1: Add WebSocket dependency​

To start, you need to add the WebSocket dependency to your project. Open your app-level build.gradle file and add the following line to the dependencies block:

implementation 'org.java-websocket:Java-WebSocket:1.5.1'

Step 2: Create a WebSocket client​

Next, create a WebSocket client class that will handle the connection to the server. In this example, we'll create a class called WebSocketClient:

import org.java_websocket.client.WebSocketClient
import org.java_websocket.handshake.ServerHandshake
import java.net.URI

class WebSocketClient(serverUri: URI) : WebSocketClient(serverUri) {

    override fun onOpen(handshakedata: ServerHandshake?) {
        // Called when the connection is established
        println("Connected to WebSocket server")
    }

    override fun onMessage(message: String?) {
        // Called when a message is received from the server
        println("Received message: $message")
    }

    override fun onClose(code: Int, reason: String?, remote: Boolean) {
        // Called when the connection is closed
        println("Connection closed: $reason")
    }

    override fun onError(ex: Exception?) {
        // Called when an error occurs
        println("Error: ${ex?.message}")
    }
}

Step 3: Create a WebSocket connection​

In your activity or fragment, create an instance of the WebSocketClient class and connect to the WebSocket server. Here's an example:

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import java.net.URI

class MainActivity : AppCompatActivity() {

    private lateinit var webSocketClient: WebSocketClient

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val serverUri = URI("ws://your-websocket-server-url")
        webSocketClient = WebSocketClient(serverUri)
        webSocketClient.connect()
    }

    override fun onDestroy() {
        super.onDestroy()
        webSocketClient.close()
    }
}

Replace "ws://your-websocket-server-url" with the actual WebSocket server URL.

Step 4: Send and receive messages​

Now that the WebSocket connection is established, you can send and receive messages to/from the server. Here are some examples:

To send a message to the server:

webSocketClient.send("Hello, server!")

To handle incoming messages from the server, modify the onMessage method in WebSocketClient class:

override fun onMessage(message: String?) {
    // Called when a message is received from the server
    println("Received message: $message")
    // Handle the message here
}

Conclusion​

This tutorial has shown you how to integrate WebSocket with a backend server in Kotlin Android. You learned how to add the WebSocket dependency, create a WebSocket client, establish a WebSocket connection, and send/receive messages.