In this article, we would be discussing one of the basic ways of communication between a program on a PC and an Android device. Here we will use the concept of Socket programming. We know communication takes place between a sender and a receiver, Socket programming involves a Client-Server setup, where a client connects to the server, send the message, and the server on the other end receives it. Now, this can be unidirectional or bidirectional based on your code.
What is Socket Programming?
Socket programming is a method of communicating between two devices connected to the same network. Two sockets, one on the client and one on the server, interact. An IP address plus a port make up a socket’s address. Over the specified port, the server application begins to listen to clients. The client connects to the server using the server’s IP address and the port it opens. After that, bidirectional communication is possible. Refer to this for a depth concept: Introducing Threads in Socket Programming in Java
Firstly, let us build the program that is to be executed on the server socket. We will make PC as a server and Android device as a client.
Step 1: Create a new project in Eclipse.
Step 2: Create a class Server.
Java
import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.net.ServerSocket;import java.net.Socket; public class Server { // declaring required variablesprivate static ServerSocket serverSocket;private static Socket clientSocket;private static InputStreamReader inputStreamReader;private static BufferedReader bufferedReader;private static String message=""; public static void main(String[] args) { try { // creating a new ServerSocket at port 4444 serverSocket = new ServerSocket(4444); } catch (IOException e) { System.out.println("Could not listen on port: 4444"); } System.out.println("Server started. Listening to the port 4444"); // we keep listening to the socket's // input stream until the message // "over" is encountered while (!message.equalsIgnoreCase("over")) { try { // the accept method waits for a new client connection // and and returns a individual socket for that connection clientSocket = serverSocket.accept(); // get the inputstream from socket, which will have // the message from the clients inputStreamReader = new InputStreamReader(clientSocket.getInputStream()); bufferedReader = new BufferedReader(inputStreamReader); // reading the message message = bufferedReader.readLine(); // printing the message System.out.println(message); // finally it is very important // that you close the sockets inputStreamReader.close(); clientSocket.close(); } catch (IOException ex) { System.out.println("Problem in message reading"); } } }} |
This program when executed creates a ServerSocket on a specific port which is 4444. Now our server starts listening to the connections made by the clients that are android devices in this case. Please refer to this article for more details: Socket Programming in Java. Now let’s program the android app for clients.
Step by Step Implementation
Step 1: Create a New Project
To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Java as the programming language.
Step 2: Working with the AndroidManifest.xml file
XML
<?xml version="1.0" encoding="utf-8"?> package="com.raghav.clientsocketapp"> <!--We require internet permission to perform networking tasks--> <uses-permission android:name="android.permission.INTERNET"/> <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/Theme.ClientSocketApp"> <activity android:name=".MainActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest> |
Step 3: Working with the activity_main.xml file
Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file.
XML
<?xml version="1.0" encoding="utf-8"?><LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".MainActivity"> <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/editText1"/> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Send" android:id="@+id/button1"/> </LinearLayout> |
Step 4: Working with the MainActivity.java file
Go to the MainActivity.java file and refer to the following code. Below is the code for the MainActivity.java file. Comments are added inside the code to understand the code in more detail.
Java
import androidx.appcompat.app.AppCompatActivity; import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.EditText;import java.io.IOException;import java.io.PrintWriter;import java.net.Socket; public class MainActivity extends AppCompatActivity { // declaring required variables private Socket client; private PrintWriter printwriter; private EditText textField; private Button button; private String message; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // reference to the text field textField = (EditText) findViewById(R.id.editText1); // reference to the send button button = (Button) findViewById(R.id.button1); // Button press event listener button.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { // get the text message on the text field message = textField.getText().toString(); // start the Thread to connect to server new Thread(new ClientThread(message)).start(); } }); } // the ClientThread class performs // the networking operations class ClientThread implements Runnable { private final String message; ClientThread(String message) { this.message = message; } @Override public void run() { try { // the IP and port should be correct to have a connection established // Creates a stream socket and connects it to the specified port number on the named host. client = new Socket("192.168.43.114", 4444); // connect to server printwriter = new PrintWriter(client.getOutputStream(),true); printwriter.write(message); // write the message to output stream printwriter.flush(); printwriter.close(); // closing the connection client.close(); } catch (IOException e) { e.printStackTrace(); } // updating the UI runOnUiThread(new Runnable() { @Override public void run() { textField.setText(""); } }); } }} |
When running on devices with api11 or higher, we would get a NetworkOnMainThreadException if we do the socket programming on the main thread. To resolve this, we can either use AsyncTask class or create a new thread. Since AsyncTask is no more supported in Android R we create a simple Thread that performs the networking part.
Getting the correct IP Address
Step 1: Enable your device’s hotspot and connect your PC to this(hotspot) network.
Step 2: Open the command prompt and write the command “ipconfig”
Step 3: Copy the IPv4 Address
Output:
