Bi-directional communication between Client and Server, using ServerSocket, Socket, DataInputStream and DataOutputStream

This example show bi-directional communication between Client and Server, both run on Android devices.

• When the Server run, it will show it's own IP and port, open a ServerSocket and wait for socket connection from clients. 
• In Client side, enter message to be sent to server, enter the server Ip and port, then clieck Connect... button, The client will connect to server using socket with DataInputStream and DataOutputStream loaded with message to send. 
• In client side, when serverSocket.accept(), it will retrieve the message sent with dataInputStream.readUTF().

Both client and server need permission of "android.permission.INTERNET" in AndroidManifest.xml.

Notice:
- All code for network operation should run in background thread.
- The code dataInputStream.readUTF() will block the program flow if no data input. (Read Pervent program blocked by DataInputStream.readUTF())

---

Example code in Server Side:

package com.example.androidserversocket;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.util.Enumeration;

import android.os.Bundle;
import android.app.Activity;
import android.widget.TextView;

public class MainActivity extends Activity {

 TextView info, infoip, msg;
 String message = "";
 ServerSocket serverSocket;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  info = (TextView) findViewById(R.id.info);
  infoip = (TextView) findViewById(R.id.infoip);
  msg = (TextView) findViewById(R.id.msg);

  infoip.setText(getIpAddress());

  Thread socketServerThread = new Thread(new SocketServerThread());
  socketServerThread.start();
 }

 @Override
 protected void onDestroy() {
  super.onDestroy();

  if (serverSocket != null) {
   try {
    serverSocket.close();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
 }

 private class SocketServerThread extends Thread {

  static final int SocketServerPORT = 8080;
  int count = 0;

  @Override
  public void run() {
   Socket socket = null;
   DataInputStream dataInputStream = null;
   DataOutputStream dataOutputStream = null;

   try {
    serverSocket = new ServerSocket(SocketServerPORT);
    MainActivity.this.runOnUiThread(new Runnable() {

     @Override
     public void run() {
      info.setText("I'm waiting here: "
        + serverSocket.getLocalPort());
     }
    });

    while (true) {
     socket = serverSocket.accept();
     dataInputStream = new DataInputStream(
       socket.getInputStream());
     dataOutputStream = new DataOutputStream(
       socket.getOutputStream());

     String messageFromClient = "";
     
     //If no message sent from client, this code will block the program
     messageFromClient = dataInputStream.readUTF();
     
     count++;
     message += "#" + count + " from " + socket.getInetAddress()
       + ":" + socket.getPort() + "\n"
       + "Msg from client: " + messageFromClient + "\n";

     MainActivity.this.runOnUiThread(new Runnable() {

      @Override
      public void run() {
       msg.setText(message);
      }
     });

     String msgReply = "Hello from Android, you are #" + count;
     dataOutputStream.writeUTF(msgReply);

    }
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    final String errMsg = e.toString();
    MainActivity.this.runOnUiThread(new Runnable() {

     @Override
     public void run() {
      msg.setText(errMsg);
     }
    });
    
   } finally {
    if (socket != null) {
     try {
      socket.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }

    if (dataInputStream != null) {
     try {
      dataInputStream.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }

    if (dataOutputStream != null) {
     try {
      dataOutputStream.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
   }
  }

 }

 private String getIpAddress() {
  String ip = "";
  try {
   Enumeration<NetworkInterface> enumNetworkInterfaces = NetworkInterface
     .getNetworkInterfaces();
   while (enumNetworkInterfaces.hasMoreElements()) {
    NetworkInterface networkInterface = enumNetworkInterfaces
      .nextElement();
    Enumeration<InetAddress> enumInetAddress = networkInterface
      .getInetAddresses();
    while (enumInetAddress.hasMoreElements()) {
     InetAddress inetAddress = enumInetAddress.nextElement();

     if (inetAddress.isSiteLocalAddress()) {
      ip += "SiteLocalAddress: "
        + inetAddress.getHostAddress() + "\n";
     }

    }

   }

  } catch (SocketException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   ip += "Something Wrong! " + e.toString() + "\n";
  }

  return ip;
 }
}

Layout:

<LinearLayout 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:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/info"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/infoip"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <TextView
            android:id="@+id/msg"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </ScrollView>

</LinearLayout>

Download the files.

---

Example code in Client Side:

package com.example.androidclient;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.net.UnknownHostException;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

 TextView textResponse;
 EditText editTextAddress, editTextPort;
 Button buttonConnect, buttonClear;
 
 EditText welcomeMsg;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  editTextAddress = (EditText) findViewById(R.id.address);
  editTextPort = (EditText) findViewById(R.id.port);
  buttonConnect = (Button) findViewById(R.id.connect);
  buttonClear = (Button) findViewById(R.id.clear);
  textResponse = (TextView) findViewById(R.id.response);
  
  welcomeMsg = (EditText)findViewById(R.id.welcomemsg);

  buttonConnect.setOnClickListener(buttonConnectOnClickListener);

  buttonClear.setOnClickListener(new OnClickListener() {

   @Override
   public void onClick(View v) {
    textResponse.setText("");
   }
  });
 }

 OnClickListener buttonConnectOnClickListener = new OnClickListener() {

  @Override
  public void onClick(View arg0) {
   
   String tMsg = welcomeMsg.getText().toString();
   if(tMsg.equals("")){
    tMsg = null;
    Toast.makeText(MainActivity.this, "No Welcome Msg sent", Toast.LENGTH_SHORT).show();
   }
   
   MyClientTask myClientTask = new MyClientTask(editTextAddress
     .getText().toString(), Integer.parseInt(editTextPort
     .getText().toString()),
     tMsg);
   myClientTask.execute();
  }
 };

 public class MyClientTask extends AsyncTask<Void, Void, Void> {

  String dstAddress;
  int dstPort;
  String response = "";
  String msgToServer;

  MyClientTask(String addr, int port, String msgTo) {
   dstAddress = addr;
   dstPort = port;
   msgToServer = msgTo;
  }

  @Override
  protected Void doInBackground(Void... arg0) {

   Socket socket = null;
   DataOutputStream dataOutputStream = null;
   DataInputStream dataInputStream = null;

   try {
    socket = new Socket(dstAddress, dstPort);
    dataOutputStream = new DataOutputStream(
      socket.getOutputStream());
    dataInputStream = new DataInputStream(socket.getInputStream());
    
    if(msgToServer != null){
     dataOutputStream.writeUTF(msgToServer);
    }
    
    response = dataInputStream.readUTF();

   } catch (UnknownHostException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    response = "UnknownHostException: " + e.toString();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    response = "IOException: " + e.toString();
   } finally {
    if (socket != null) {
     try {
      socket.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }

    if (dataOutputStream != null) {
     try {
      dataOutputStream.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }

    if (dataInputStream != null) {
     try {
      dataInputStream.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
   }
   return null;
  }

  @Override
  protected void onPostExecute(Void result) {
   textResponse.setText(response);
   super.onPostExecute(result);
  }

 }

}

Layout:

<LinearLayout 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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />
    <EditText 
        android:id="@+id/welcomemsg"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Say hello to server" />
    <EditText 
        android:id="@+id/address"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="dstAddress" />
    <EditText 
        android:id="@+id/port"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="dstPort" />
    <Button 
        android:id="@+id/connect"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Connect..."/>
    <Button 
        android:id="@+id/clear"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Clear"/>
    <TextView
        android:id="@+id/response"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>

Download the files.

---

Client and Server run on WiFi share hotspot:

The following video, at 1:22, show it work when both client and server connect to the shared WiFi network from server hotspot.



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