Client-Server Programming in Android

This example demonstrate about Client-Server Programming in Android
Need Server and Client Project
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version = "1.0" encoding = "utf-8"?>
<RelativeLayout xmlns:android = "http://schemas.android.com/apk/res/android"
   xmlns:tools = "http://schemas.android.com/tools"
   android:layout_width = "match_parent"
   android:layout_height = "match_parent"
   android:layout_margin = "16dp"
   tools:context = ".MainActivity">
   <TextView
      android:id = "@+id/tvIP"
      android:layout_width = "wrap_content"
      android:layout_height = "wrap_content"
      android:textAppearance = "@style/Base.TextAppearance.AppCompat.Medium" />
   <TextView
      android:id = "@+id/tvPort"
      android:layout_width = "wrap_content"
      android:layout_height = "wrap_content"
      android:layout_below = "@+id/tvIP"
      android:textAppearance = "@style/Base.TextAppearance.AppCompat.Medium" />
   <TextView
      android:id = "@+id/tvConnectionStatus"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_below = "@+id/tvPort"
      android:textAppearance = "@style/Base.TextAppearance.AppCompat.Medium" />
   <TextView
      android:id = "@+id/tvMessages"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_above = "@+id/etMessage"
      android:layout_below = "@+id/tvConnectionStatus"
      android:inputType = "textMultiLine"
      android:textAppearance = "@style/Base.TextAppearance.AppCompat.Medium" />
   <EditText
      android:id = "@+id/etMessage"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_above = "@+id/btnSend"
      android:hint = "Enter Message"
      android:inputType = "text" />
   <Button
      android:id = "@+id/btnSend"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_alignParentBottom = "true"
      android:text = "SEND" />
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.java
package com.server.myapplication.server;
import android.annotation.SuppressLint;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

@SuppressLint("SetTextI18n")
public class MainActivity extends AppCompatActivity {
   ServerSocket serverSocket;
   Thread Thread1 = null;
   TextView tvIP, tvPort;
   TextView tvMessages;
   EditText etMessage;
   Button btnSend;
   public static String SERVER_IP = "";
   public static final int SERVER_PORT = 8080;
   String message;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      tvIP = findViewById(R.id.tvIP);
      tvPort = findViewById(R.id.tvPort);
      tvMessages = findViewById(R.id.tvMessages);
      etMessage = findViewById(R.id.etMessage);
      btnSend = findViewById(R.id.btnSend);
      try {
         SERVER_IP = getLocalIpAddress();
      } catch (UnknownHostException e) {
         e.printStackTrace();
      }
      Thread1 = new Thread(new Thread1());
      Thread1.start();
      btnSend.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            message = etMessage.getText().toString().trim();
            if (!message.isEmpty()) {
               new Thread(new Thread3(message)).start();
            }
         }
      });
   }
   private String getLocalIpAddress() throws UnknownHostException {
      WifiManager wifiManager = (WifiManager) getApplicationContext().getSystemService(WIFI_SERVICE);
      assert wifiManager ! = null;
      WifiInfo wifiInfo = wifiManager.getConnectionInfo();
      int ipInt = wifiInfo.getIpAddress();
      return InetAddress.getByAddress(ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN).putInt(ipInt).array()).getHostAddress();
   }
   private PrintWriter output;
   private BufferedReader input;
   class Thread1 implements Runnable {
      @Override
      public void run() {
         Socket socket;
         try {
            serverSocket = new ServerSocket(SERVER_PORT);
            runOnUiThread(new Runnable() {
               @Override
               public void run() {
                  tvMessages.setText("Not connected");
                  tvIP.setText("IP: " + SERVER_IP);
                  tvPort.setText("Port: " + String.valueOf(SERVER_PORT));
               }
            });
            try {
               socket = serverSocket.accept();
               output = new PrintWriter(socket.getOutputStream());
               input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
               runOnUiThread(new Runnable() {
                  @Override
                  public void run() {
                     tvMessages.setText("Connected\n");
                  }
               });
               new Thread(new Thread2()).start();
            } catch (IOException e) {
               e.printStackTrace();
            }
         } catch (IOException e) {
            e.printStackTrace();
         }
      }
   }
   private class Thread2 implements Runnable {
      @Override
      public void run() {
         while (true) {
            try {
               final String message = input.readLine();
               if (message ! = null) {
                  runOnUiThread(new Runnable() {
                     @Override
                     public void run() {
                        tvMessages.append("client:" + message + "\n");
                     }
                  });
               } else {
                  Thread1 = new Thread(new Thread1());
                  Thread1.start();
                  return;
               }
            } catch (IOException e) {
               e.printStackTrace();
            }
         }
      }
   }
   class Thread3 implements Runnable {
      private String message;
      Thread3(String message) {
         this.message = message;
      }
      @Override
      public void run() {
         output.write(message);
         output.flush();
         runOnUiThread(new Runnable() {
            @Override
            public void run() {
               tvMessages.append("server: " + message + "\n");
               etMessage.setText("");
            }
         });
      }
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version = "1.0" encoding = "utf-8"?>
<manifest xmlns:android = "http://schemas.android.com/apk/res/android"
   package = "com.example.myapplication">
   <uses-permission android:name = "android.permission.ACCESS_WIFI_STATE" />
   <uses-permission android:name = "android.permission.ACCESS_NETWORK_STATE" />
   <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/AppTheme">
      <activity android:name = ".MainActivity"
         android:label = "Server">
         <intent-filter>
            <action android:name = "android.intent.action.MAIN" />
            <category android:name = "android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version = "1.0" encoding = "utf-8"?>
<RelativeLayout xmlns:android = "http://schemas.android.com/apk/res/android"
   xmlns:tools = "http://schemas.android.com/tools"
   android:layout_width = "match_parent"
   android:layout_height = "match_parent"
   android:layout_margin = "16dp"
   tools:context = ".MainActivity">
   <EditText
      android:id = "@+id/etIP"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:hint = "IP-Address"
      android:inputType = "text" />
   <EditText
      android:id = "@+id/etPort"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_below = "@+id/etIP"
      android:hint = "Port No"
      android:inputType = "number" />
   <Button
      android:id = "@+id/btnConnect"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_below = "@+id/etPort"
      android:layout_gravity = "center"
      android:layout_marginTop = "16dp"
      android:text = "Connect To Server" />
   <TextView
      android:id = "@+id/tvMessages"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_above = "@+id/etMessage"
      android:layout_below = "@+id/btnConnect"
      android:inputType = "textMultiLine"
      android:textAppearance = "@style/Base.TextAppearance.AppCompat.Medium" />
   <EditText
      android:id = "@+id/etMessage"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_above = "@+id/btnSend"
      android:hint = "Enter Message"
      android:inputType = "text" />
   <Button
      android:id = "@+id/btnSend"
      android:layout_width = "match_parent"
      android:layout_height = "wrap_content"
      android:layout_alignParentBottom = "true"
      android:text = "SEND" />
</RelativeLayout>
Step 3 − Add the following code to res/layout/MainActivity.java.
package com.client.myapplication.client;
import android.annotation.SuppressLint;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

@SuppressLint("SetTextI18n")
public class MainActivity extends AppCompatActivity {
   Thread Thread1 = null;
   EditText etIP, etPort;
   TextView tvMessages;
   EditText etMessage;
   Button btnSend;
   String SERVER_IP;
   int SERVER_PORT;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      etIP = findViewById(R.id.etIP);
      etPort = findViewById(R.id.etPort);
      tvMessages = findViewById(R.id.tvMessages);
      etMessage = findViewById(R.id.etMessage);
      btnSend = findViewById(R.id.btnSend);
      Button btnConnect = findViewById(R.id.btnConnect);
      btnConnect.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            tvMessages.setText("");
            SERVER_IP = etIP.getText().toString().trim();
            SERVER_PORT = Integer.parseInt(etPort.getText().toString().trim());
            Thread1 = new Thread(new Thread1());
            Thread1.start();
         }
      });
      btnSend.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            String message = etMessage.getText().toString().trim();
            if (!message.isEmpty()) {
               new Thread(new Thread3(message)).start();
            }
         }
      });
   }
   private PrintWriter output;
   private BufferedReader input;
   class Thread1 implements Runnable {
      @Override
      public void run() {
         Socket socket;
         try {
            socket = new Socket(SERVER_IP, SERVER_PORT);
            output = new PrintWriter(socket.getOutputStream());
            input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            runOnUiThread(new Runnable() {
               @Override
               public void run() {
                  tvMessages.setText("Connected\n");
               }
            });
            new Thread(new Thread2()).start();
         } catch (IOException e) {
            e.printStackTrace();
         }
      }
   }
   class Thread2 implements Runnable {
      @Override
      public void run() {
         while (true) {
            try {
               final String message = input.readLine();
               if (message ! = null) {
                  runOnUiThread(new Runnable() {
                     @Override
                     public void run() {
                        tvMessages.append("server: " + message + "\n");
                     }
                  });
               } else {
                  Thread1 = new Thread(new Thread1());
                  Thread1.start();
                  return;
               }
            } catch (IOException e) {
               e.printStackTrace();
            }
         }
      }
   }
   class Thread3 implements Runnable {
      private String message;
      Thread3(String message) {
         this.message = message;
      }
      @Override
      public void run() {
         output.write(message);
         output.flush();
         runOnUiThread(new Runnable() {
            @Override
            public void run() {
               tvMessages.append("client: " + message + "\n");
               etMessage.setText("");
            }
         });
      }
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version = "1.0" encoding = "utf-8"?>
<manifest xmlns:android = "http://schemas.android.com/apk/res/android"
   package = "com.client.myapplication.client">
   <uses-permission android:name = "android.permission.INTERNET" />
   <uses-permission android:name = "android.permission.ACCESS_NETWORK_STATE" />
   <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/AppTheme">
      <activity
         android:name = "com.client.myapplication.client.MainActivity"
         android:label = "Client">
         <intent-filter>
            <action android:name = "android.intent.action.MAIN" />
            <category android:name = "android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your both server and client application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run    icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –
Click here to download the project code