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How can I send a String through socket from client then get the return from the server?

I am trying to make a simple java android app
I want to send an order from my computer (client) to my android app (server) the the mobile (server) must send the return back to the client (computer)
Client (computer)
public class Main {
public static void main(String[] args) {
Scanner sx = new Scanner(System.in);
String ln = sx.next();
try {
Socket s = new Socket("192.168.2.2", 4040);
s.setSoTimeout(4000);
DataOutputStream dos = new DataOutputStream(s.getOutputStream());
dos.writeUTF(ln);
dos.flush();
s.close();
System.out.println("Done....");
} catch (Exception e) {
System.out.println(e.toString());
}
}
}
Server (android app)
public class MainActivity extends Activity {
EditText portfield, ipfield;
LinearLayout player;
SharedPreferences sp;
SharedPreferences.Editor ed;
String myip, myport;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
player = (LinearLayout) findViewById(R.id.player);
portfield = (EditText) findViewById(R.id.portfield);
ipfield = (EditText) findViewById(R.id.ipfield);
sp = getSharedPreferences("okayawalas2423", MODE_PRIVATE);
ed = sp.edit();
myport = sp.getString("myport", null);
myip = sp.getString("myip", null);
runit();
}
public void runit() {
if (myport != null && myip != null) {
final String myport;
final String myip;
startspy();
}
}
public void startspy() {
player.removeAllViews();
Thread th = new Thread(new Runnable() {
public void run() {
eim();
}
});
th.start();
}
public void eim() {
try {
ServerSocket server = new ServerSocket(Integer.parseInt(myport));
say("Server Connected Successfully .... ");
while (true) {
Socket skt = server.accept();
say("The Server Request Has Been Accepted .... ");
DataInputStream dis = new DataInputStream(skt.getInputStream());
String purein = dis.readUTF();
dsay("Data Has Been Sent Right Now To /// and it contains : \n [[[ " + dis.readUTF() + " ]]]");
DataOutputStream dos = new DataOutputStream(skt.getOutputStream());
String outword = doit(purein);
dos.writeUTF(outword);
dos.flush();
dis.close();
dos.close();
skt.close();
}
} catch (Exception e) {
TextView tz = new TextView(this);
tz.setText(e.toString());
player.setGravity(Gravity.CENTER);
player.addView(tz);
}
}
public void stt(View v) {
if (portfield.getText().toString().equals("") || ipfield.getText().toString().equals("")) {
Toast.makeText(this, "Insert All Data !!", Toast.LENGTH_LONG).show();
} else {
ed.putString("myport", portfield.getText().toString());
ed.putString("myip", ipfield.getText().toString());
ed.commit();
startspy();
}
}
public String doit(String p) {
String funRes = "none";
funRes = p;
return funRes;
}
public void say(String s) {
TextView tz = new TextView(this);
tz.setText(s);
player.setGravity(Gravity.CENTER);
player.addView(tz);
}
public void dsay(String s) {
Toast.makeText(this, s, Toast.LENGTH_SHORT).show();
}
}
I type the message on the computer (client) when I press ENTER, I get the "Done..." but the android app gets down!!

Why is my port source changing with every UDP message I send?

I'm tracking the UDP messages I'm sending from my android phone on Wireshark, but the source port number changes every time I send a message.
So I have two questions:
Is this bad if I want to receive messages back? Or would it be find, just each received message comes through a different port?
If the answer to 1) is yes it is bad, then what should I do to change that?
Here's my code:
edit: Full code
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
public static final int SERVERPORT = 1111;
public static final String SERVER_IP = "255.255.255.255";
private LinearLayout msgList;
private EditText edMessage;
private int clientTextColor;
private ClientThread clientThread;
private Thread thread;
private Handler handler;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
msgList = findViewById(R.id.msgList);
edMessage = findViewById(R.id.edMessage);
clientTextColor = ContextCompat.getColor(this, R.color.colorAccent);
handler = new Handler();
}
// Just for displaying messages on device
public TextView textView(String message, int color) {...}
public void showMessage(final String message, final int color) {
handler.post(new Runnable() {
#Override
public void run() {
msgList.addView(textView(message, color));
}
});
}
// Implementation
#Override
public void onClick(View view) {
if(view.getId() == R.id.clear) {
msgList.removeAllViews();
}
if (view.getId() == R.id.send_data) {
// Starting thread
clientThread = new ClientThread();
thread = new Thread(clientThread);
thread.start();
String clientMessage = edMessage.getText().toString().trim(); // Client's Message
showMessage(clientMessage, Color.BLUE); // Just display
if (null != clientThread) {
clientThread.sendMessage(clientMessage + "\r\n");
}
}
}
class ClientThread implements Runnable {
byte[] buffer = new byte[1024];
#Override
public void run() {
try {
while (true) {
DatagramSocket ds = new DatagramSocket(SERVERPORT);
DatagramPacket dp = new DatagramPacket(buffer, buffer.length);
ds.receive(dp);
String serverMsg = new String(dp.getData(), 0, dp.getLength());
showMessage("Server: " + serverMsg, clientTextColor);
ds.close();
}
} catch (UnknownHostException e1) {
e1.printStackTrace();
}
}
void sendMessage(final String message) { // Called by "Send Data" button
new Thread(new Runnable() {
#Override
public void run() {
try {
byte[] msg = message.getBytes();
InetAddress ip = InetAddress.getByName(SERVER_IP);
DatagramSocket socket = new DatagramSocket();
DatagramPacket packet = new DatagramPacket(msg, msg.length, ip, SERVERPORT);
socket.setBroadcast(true);
socket.send(packet);
} catch(Exception e) {
e.printStackTrace();
}
}
}).start();
}
}
String getTime() {
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
return sdf.format(new Date());
}
#Override
protected void onDestroy() {
super.onDestroy();
if (null != clientThread) {
clientThread.sendMessage("Disconnect");
clientThread = null;
}
}
}

ObjectOutputStream throwing Exception

I'm trying to write a simple client/server program, where the client is an android app and the server is a Raspberry Pi 4. All I want to do is allow the client to type a message and have the Raspberry Pi display the message on the terminal. However, my app keeps throwing an exception at the out.writeObject(message_text) line in the sendMessage() method.
public class MainActivity extends AppCompatActivity {
private EditText message;
private Button send;
private ObjectOutputStream out;
private Socket socket;
private String raspi_ip = "enter ip here";
private int raspi_portnum = 12345;
Client client;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
message = findViewById(R.id.message_text);
send = findViewById(R.id.send_button);
try{
client = new Client(raspi_ip,raspi_portnum);
client.start();
} catch (Exception e){
AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);
dialog.setTitle("Error! ").setMessage("Couldn't connect to server.").setNeutralButton("OK", null).create().show();
}
send.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
client.sendMessage();
}
});
}
private void closeConnection(){
try{
out.close();
socket.close();
} catch (Exception e){
e.printStackTrace();
}
}
#Override
protected void onStop(){
super.onStop();
closeConnection();
}
private class Client extends Thread {
private String ip_address;
private int port_number;
public Client(String ipaddress,int portnum){
this.ip_address = ipaddress;
this.port_number = portnum;
}
#Override
public void run() {
super.run();
connectToServer(ip_address,port_number);
}
public void connectToServer(String ipaddress, int portnum){
try{
socket = new Socket(InetAddress.getByName(ipaddress),portnum);
out = new ObjectOutputStream(socket.getOutputStream());
out.flush();
}catch (Exception e){
AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);
dialog.setTitle("Error! ").setMessage("Couldn't connect to server.").setNeutralButton("OK", null).create().show();
}
}
public void sendMessage(){
String message_text = message.getText().toString();
try{
out.writeObject(message_text);
out.flush();
} catch (Exception e) {
AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);
dialog.setTitle("Error! ").setMessage("IO Exception.").setNeutralButton("OK", null).create().show();
}
}
}
}
Here is the server side java program:
import java.io.ObjectInputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class RaspPiServer {
private ServerSocket server;
public RaspPiServer(){
}
public static void main(String[] args){
RaspPiServer server = new RaspPiServer();
server.runServer();
}
public void runServer(){
try{
server = new ServerSocket(12345,100);
while (true){
new Controller(server.accept()).start();
}
} catch(Exception e){
e.printStackTrace();
}
}
private class Controller extends Thread {
private Socket socket;
private ObjectInputStream input;
private String in;
public Controller(Socket socket){
this.socket = socket;
System.out.println("New client at " + socket.getRemoteSocketAddress());
}
#Override
public void run(){
try{
input = new ObjectInputStream(socket.getInputStream());
while (!(in = (String)input.readObject()).equals("close")){
System.out.println(in);
}
} catch(Exception e){
e.printStackTrace();
} finally {
closeConnection();
System.out.println("Connection with client # " + socket.getRemoteSocketAddress() + " closed");
}
}
private void closeConnection() {
try {
input.close();
socket.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
Is there an easy fix here, or am I missing something bigger?

Android multi threading UI update

I'm trying to run a UDP connection with external equipment. I want it to send a message to the equipment every 3 second and read the response.
I created 3 classes: main, sender and receive.
I open a Runnable for both sender and receive and let them sleep for 3 seconds before continue.
My problem is, when i push the button on the screen, the messages are send and received, however they are not updated on my screen because the update line is not in a loop. How do i tell it to update the screen every 3 second? the code for reading the message and show it, is this:
textViewState.setText(udpReceive.receivedMessage);
Code
public class MainActivity extends AppCompatActivity {
public static TextView textViewState;
public static Context context;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textViewState = (TextView) findViewById(R.id.textView);
context = getApplicationContext();
}
public void buttonConnect(View v) {
(new Thread(new udpSender())).start();
(new Thread(new udpReceive())).start();
textViewState.setText(udpReceive.receivedMessage);
}
}
Class to send a message:
public class udpSender implements Runnable {
public void run() {
while (true) {
String messageStr = "Hello Android!";
int server_port = 8888;
DatagramSocket s = null;
try {
s = new DatagramSocket();
} catch (SocketException e) {
e.printStackTrace();
}
InetAddress local = null;
try {
local = InetAddress.getByName("192.168.43.159");
} catch (UnknownHostException e) {
e.printStackTrace();
}
int msg_length = messageStr.length();
byte[] message = messageStr.getBytes();
DatagramPacket p = new DatagramPacket(message, msg_length, local, server_port);
try {
s.send(p);
} catch (IOException e) {
e.printStackTrace();
}
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
Class to receive message from udp
public class udpReceive implements Runnable {
private static final int MAX_UDP_DATAGRAM_LEN = 100;
private static final int UDP_SERVER_PORT = 8888;
public static String receivedMessage;
public void run() {
while (true) {
String message;
byte[] lmessage = null;
lmessage = new byte[MAX_UDP_DATAGRAM_LEN];
DatagramPacket packet = null;
DatagramSocket socket = null;
try {
packet = new DatagramPacket(lmessage, lmessage.length);
socket = new DatagramSocket(UDP_SERVER_PORT);
socket.receive(packet);
message = new String(lmessage, 0, packet.getLength());
receivedMessage = message;
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (socket != null) {
socket.close();
}
}
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

In any class that is in another thread, try doing this
Handler handler = new Handler(getActivity().getMainLooper());
handler.post(new Runnable(){
// your TextView goes here
})

Only the UI thread (main thread) can access UI elements
// Your message receiving class
...
message = new String(lmessage, 0, packet.getLength());
final String message_received = new String(lmessage, 0, packet.getLength());
...
MainActivity.context.runOnUiThread(new Runnable() {
#Override
public void run() {
MainActivity.textViewState.setText(message_received);
}
});
...

I found a solution based on both of your answers :) Thank you
MainActivity class:
public static Handler UIHandler;
static {
UIHandler = new Handler(Looper.getMainLooper());
}
public static void runOnUI(Runnable runnable) {
UIHandler.post(runnable);
}
receive class
MainActivity.runOnUI(new Runnable() {
public void run() {
MainActivity.textViewState.setText(message_received);
}
});

Server Ip at Client side using Sockets

I need to create an application using android socket level programming, I created a connection between server and client but I need to show waiting server IP list at client side and select one IP from the list and establish a connection between them.
Here is my code for server side
public class Server extends AppCompatActivity {
private static final String TAG = "ServerActivity";
private TextView tvServerStatus;
private TextView recievemsg;
InetAddress receiverAddress;
public static String SERVERIP = "";
DatagramSocket datagramSocket;
public static final int SERVERPORT = 8080;
private Handler handler = new Handler();
Handler updateConversationHandler;
private ServerSocket serverSocket;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_server);
updateConversationHandler = new Handler();
tvServerStatus = (TextView) findViewById(R.id.tvServerStatus);
recievemsg=(TextView)findViewById(R.id.send_msg);
SERVERIP = getLocalIpAddress();
Thread fst = new Thread(new ServerThread());
fst.start();
try {
datagramSocket = new DatagramSocket(8080);
byte[] buffer = "0123456789".getBytes();
byte[] address=SERVERIP.getBytes();
receiverAddress = InetAddress.getByAddress(address);
DatagramPacket packet = new DatagramPacket(
buffer, buffer.length, receiverAddress, 8080);
datagramSocket.send(packet);
} catch (SocketException e) {
e.printStackTrace();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
private String getLocalIpAddress() {
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 ServerThread implements Runnable {
#Override
public void run() {
try {
Log.e(TAG, "Server IP: " + SERVERIP);
if (SERVERIP != null) {
handler.post(new Runnable() {
#Override
public void run() {
tvServerStatus.setText("Listening On Ip: " + SERVERIP);
}
});
serverSocket = new ServerSocket(SERVERPORT);
while (!Thread.currentThread().isInterrupted()) {
{
try {
// LISTEN FOR INCOMING CLIENTS
Socket client = serverSocket.accept();
CommunicationThread commThread = new CommunicationThread(client);
new Thread(commThread).start();
// Log.e(TAG, "Client Socket: " + client);
// new Clients_Handle(client, ROOT_DIRECTORY).start();
}
catch (IOException e) {
e.printStackTrace();
}
}
}
} else {
handler.post(new Runnable() {
#Override
public void run() {
tvServerStatus.setText("Couldn't detect internet connection.");
}
});
}
} catch (IOException e) {
handler.post(new Runnable() {
#Override
public void run() {
tvServerStatus.setText("Error");
}
});
e.printStackTrace();
}
}
}
class CommunicationThread implements Runnable {
private Socket clientSocket;
private BufferedReader input;
public CommunicationThread(Socket clientSocket) {
this.clientSocket = clientSocket;
try {
this.input = new BufferedReader(new InputStreamReader(this.clientSocket.getInputStream()));
} catch (IOException e) {
e.printStackTrace();
}
}
public void run() {
while (!Thread.currentThread().isInterrupted()) {
try {
String read = input.readLine();
updateConversationHandler.post(new updateUIThread(read));
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
class updateUIThread implements Runnable {
private String msg;
public updateUIThread(String str) {
this.msg = str;
}
#Override
public void run() {
recievemsg.setText(recievemsg.getText().toString() + "Client Says: " + msg + "\n");
}
}
#Override
protected void onDestroy() {
super.onDestroy();
try {
// MAKE SURE YOU CLOSE THE SOCKET UPON EXITING
serverSocket.close();
Log.e(TAG,"Socket Closed");
} catch (IOException e) {
e.printStackTrace();
}
}
}
And here is my client side code
public class Clientss extends AppCompatActivity {
private static final String TAG = "Client_Activity";
private EditText etServerIp;
private EditText etMsg;
private Button btnConnectClients;
private Button btnSendMsg;
private TextView textIn;
private String serverIpAddress = "";
private String t;
private boolean connected = false;
DatagramSocket datagramSocket;
DatagramPacket packet;
private Socket socket;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_clientss);
Log.e(TAG, "ONCREATE METHOD");
textIn = (TextView)findViewById(R.id.txt_msg);
initializations();
eventClickListener();
try {
datagramSocket = new DatagramSocket(8080);
byte[] buffer = new byte[10];
packet = new DatagramPacket(buffer, buffer.length);
datagramSocket.receive(packet);
byte[] buff = packet.getData();
textIn.setText(buff.toString());
System.out.println("this is incoming ip"+buff.toString());
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
// textIn.setText(t);
}
private void eventClickListener() {
btnConnectClients.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (!connected) {
serverIpAddress = etServerIp.getText().toString().trim();
connectsClient();
}
}
});
btnSendMsg.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String msg = etMsg.getText().toString().trim();
ClientResponseTask clientResponseTask=new ClientResponseTask(msg);
clientResponseTask.execute();
}
});
}
private void connectsClient() {
if (!serverIpAddress.equals("")) {
Thread cThread = new Thread(new ClientThread());
cThread.start();
}
}
private void initializations() {
etServerIp = (EditText) findViewById(R.id.etServerIp);
etMsg = (EditText) findViewById(R.id.etMsg);
btnSendMsg = (Button) findViewById(R.id.btnMsgSend);
btnConnectClients = (Button) findViewById(R.id.btnConnect);
}
private class ClientThread implements Runnable {
#Override
public void run() {
try {
InetAddress serverAddr = InetAddress.getByName(serverIpAddress);
Log.e(TAG, "C: Connecting...");
socket = new Socket(serverAddr, Server.SERVERPORT);
System.out.println("this is socket"+socket);
connected = true;
Message msg = handler.obtainMessage();
msg.arg1 = 1;
handler.sendMessage(msg);
//showToast("");
Log.e(TAG, "C: Connected..." + socket);
} catch (Exception e) {
Log.e(TAG, "C: Error", e);
connected = false;
}
}
}
private final Handler handler = new Handler() {
public void handleMessage(Message msg) {
if(msg.arg1 == 1)
Toast.makeText(getApplicationContext(),"Connected...", Toast.LENGTH_LONG).show();
}
};
#Override
protected void onDestroy() {
if (socket != null) try {
socket.close();
Log.e(TAG, "C: Socket Closed.");
} catch (IOException e) {
e.printStackTrace();
} finally
{
try
{
socket.close();
}
catch(Exception e){}
}
super.onDestroy();
}
protected class ClientResponseTask extends AsyncTask<Void,Void,Void> {
String msg;
ClientResponseTask(String msg){
this.msg=msg;
}
#Override
protected Void doInBackground(Void... params) {
if (connected) {
try {
PrintWriter out = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())), true);
out.println(msg);
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (Exception e) {
Log.e(TAG, "Error", e);
}
}
else {
connectsClient();
}
return null;
}
}
}
Please help me to find a solution.