File transfer via Socket, between Android devices

This example show how to transfer file between Android devices, via Socket.

In server side, it start a Thread to run a ServerSocket and wait for connection. Once connected, start another Thread to send file.

In client side, start a Thread to connect to server and download file.

In this example, the file to send and receive are fixed test.txt in external storage.

---

Server Side:

MainActivity.java

package com.example.androidsocketfiletransferserver;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
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.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.os.Environment;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends ActionBarActivity {

 TextView infoIp, infoPort;

 static final int SocketServerPORT = 8080;
 ServerSocket serverSocket;
 
 ServerSocketThread serverSocketThread;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  infoIp = (TextView) findViewById(R.id.infoip);
  infoPort = (TextView) findViewById(R.id.infoport);

  infoIp.setText(getIpAddress());
  
  serverSocketThread = new ServerSocketThread();
  serverSocketThread.start();
 }

 @Override
 protected void onDestroy() {
  super.onDestroy();
  
  if (serverSocket != null) {
   try {
    serverSocket.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;
 }
 
 public class ServerSocketThread extends Thread {

  @Override
  public void run() {
   Socket socket = null;
   
   try {
    serverSocket = new ServerSocket(SocketServerPORT);
    MainActivity.this.runOnUiThread(new Runnable() {

     @Override
     public void run() {
      infoPort.setText("I'm waiting here: " 
       + serverSocket.getLocalPort());
     }});
    
    while (true) {
     socket = serverSocket.accept();
     FileTxThread fileTxThread = new FileTxThread(socket);
     fileTxThread.start();
    }
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } finally {
    if (socket != null) {
     try {
      socket.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
   }
  }

 }
 
 public class FileTxThread extends Thread {
  Socket socket;
  
  FileTxThread(Socket socket){
   this.socket= socket;
  }

  @Override
  public void run() {
   File file = new File(
     Environment.getExternalStorageDirectory(), 
     "test.txt");
   
   byte[] bytes = new byte[(int) file.length()];
   BufferedInputStream bis;
   try {
    bis = new BufferedInputStream(new FileInputStream(file));
    bis.read(bytes, 0, bytes.length);
    OutputStream os = socket.getOutputStream();
    os.write(bytes, 0, bytes.length);
    os.flush();
    socket.close();
    
    final String sentMsg = "File sent to: " + socket.getInetAddress();
    MainActivity.this.runOnUiThread(new Runnable() {

     @Override
     public void run() {
      Toast.makeText(MainActivity.this, 
        sentMsg, 
        Toast.LENGTH_LONG).show();
     }});
    
   } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } finally {
    try {
     socket.close();
    } catch (IOException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }
   }
   
  }
 }
}

activity_main.xml

<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="com.example.androidsocketfiletransferserver.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:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="File Transfer Server"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/infoport"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="italic" />

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

</LinearLayout>

Add permission of "android.permission.INTERNET" and "android.permission.READ_EXTERNAL_STORAGE" to AndroidManifest.xml.

Download the files.

---

Client Side:

MainActivity.java

package com.example.androidsocketfiletransferclient;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.Socket;
import android.support.v7.app.ActionBarActivity;
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;
import android.os.Bundle;
import android.os.Environment;

public class MainActivity extends ActionBarActivity {

 EditText editTextAddress;
 Button buttonConnect;
 TextView textPort;

 static final int SocketServerPORT = 8080;

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

  editTextAddress = (EditText) findViewById(R.id.address);
  textPort = (TextView) findViewById(R.id.port);
  textPort.setText("port: " + SocketServerPORT);
  buttonConnect = (Button) findViewById(R.id.connect);
  
  buttonConnect.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View v) {
    ClientRxThread clientRxThread = 
     new ClientRxThread(
      editTextAddress.getText().toString(), 
      SocketServerPORT);
    
    clientRxThread.start();
   }});
 }

 private class ClientRxThread extends Thread {
  String dstAddress;
  int dstPort;

  ClientRxThread(String address, int port) {
   dstAddress = address;
   dstPort = port;
  }

  @Override
  public void run() {
   Socket socket = null;
   
   try {
    socket = new Socket(dstAddress, dstPort);
    
    File file = new File(
      Environment.getExternalStorageDirectory(), 
      "test.txt");
    
    byte[] bytes = new byte[1024];
    InputStream is = socket.getInputStream();
       FileOutputStream fos = new FileOutputStream(file);
       BufferedOutputStream bos = new BufferedOutputStream(fos);
       int bytesRead = is.read(bytes, 0, bytes.length);
       bos.write(bytes, 0, bytesRead);
       bos.close();
       socket.close();
       
       MainActivity.this.runOnUiThread(new Runnable() {

     @Override
     public void run() {
      Toast.makeText(MainActivity.this, 
        "Finished", 
        Toast.LENGTH_LONG).show();
     }});
    
   } catch (IOException e) {

    e.printStackTrace();
    
    final String eMsg = "Something wrong: " + e.getMessage();
    MainActivity.this.runOnUiThread(new Runnable() {

     @Override
     public void run() {
      Toast.makeText(MainActivity.this, 
        eMsg, 
        Toast.LENGTH_LONG).show();
     }});
    
   } finally {
    if(socket != null){
     try {
      socket.close();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
   }
  }
 }

}

activity_main.xml

<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="com.example.androidsocketfiletransferclient.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:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="File Transfer Client"
        android:textStyle="bold" />

    <EditText
        android:id="@+id/address"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="dstAddress" />

    <TextView
        android:id="@+id/port"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/connect"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Connect..." />

</LinearLayout>

Add permission of "android.permission.INTERNET" and "android.permission.WRITE_EXTERNAL_STORAGE" to AndroidManifest.xml.

Download the files.

---

Next:
- Transfer image between Android devices, via Socket

More example of Android Network programming
- Bi-directional communication between Client and Server, using ServerSocket, Socket, DataInputStream and DataOutputStream