Android chat client: socket connection

Question

im new to Android. First I wrote a Chat_Client and Server in Java. It works great.

Then i tried to convert it to an working Android app, I always get the message "Cannot connect to the Server! Try again!" so it's obviously something wrong with the Socket connection attempt, but I can't figure out what it is.

Background knowledge:
- Im connected to my root server and take a look at the chat_server process. It's running!
- I tried to connect from an other chat_client on my PC to the chat_server. It works!
- The host and the port are the right one. Checked it a few times.
- Permissions are set <uses-permission android:name="android.permission.INTERNET"/> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/> <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
- I can run the app on my Nexus 5
- There are no Errors listed in LogCat or the Console, it seems like it run normally..

My chat_client code:

package de.Voldemord.chatter;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.*;
import java.io.*;
import java.net.*;
import java.util.*;

public class MainActivity extends Activity implements OnClickListener{
    private Button btn;
    private EditText et_send;
    private EditText et_chat;
    private String s_username = "Voldemord", s_host = "www.example.com";         // !Example host!
    private int s_port = 2222;                                                   // !Example port!
    private Socket socket = null;
    private BufferedReader in;
    private PrintWriter out;
    @SuppressWarnings({ "unchecked", "rawtypes" })
    ArrayList<String> users = new ArrayList();
    boolean isConnected = false;

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

    et_send = (EditText) findViewById(R.id.sendTextView);
    et_chat = (EditText) findViewById(R.id.chatTextView);

    btn = (Button) findViewById(R.id.btn);
    btn.setOnClickListener(this);


    if (isConnected == false){
        try{
            socket = new Socket(InetAddress.getByName(s_host), s_port);
            InputStreamReader streamreader = new InputStreamReader(socket.getInputStream());
            in = new BufferedReader(streamreader);
            out = new PrintWriter(socket.getOutputStream());
            out.println(s_username + ":has connected.:Connect");
            out.flush(); 
            isConnected = true; 
        }catch (Exception ex){
            et_chat.append("Cannot Connect! Try Again. \n"+ socket);
        }

        ListenThread();

    }else if (isConnected == true){
        et_chat.append("You are already connected. \n");
    }

}

protected void onDestroy(){
    super.onDestroy();
    sendDisconnect();
    Disconnect();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onClick(View v) {   
    String nothing = "";
    if ((et_send.getText()).equals(nothing)) {
        et_send.setText("");
        et_send.requestFocus();
    } else {
        try {
           out.println(s_username + ":" + et_send.getText() + ":" + "Chat");
           out.flush(); // flushes the buffer
        } catch (Exception ex) {
            et_chat.append("Message was not sent. \n");
        }
        et_send.setText("");
        et_send.requestFocus();
    }

    et_send.setText("");
    et_send.requestFocus();
}

public void sendDisconnect(){
    String bye = (s_username + ": :Disconnect");
    try{
        out.println(bye);
        out.flush();
    }catch (Exception e){
        et_chat.append("Could not send Disconnect message.\n");
    }
}

public void Disconnect(){
    try{
        et_chat.append("Disconnected.\n");
        socket.close();
    }catch (Exception e){
        et_chat.append("Failed to disconnect.\n");
    }
    isConnected = false;
}

public void ListenThread(){
    Thread IncomingReader = new Thread(new IncomingReader());
    IncomingReader.start();
}

public void userAdd(String user){
    users.add(user);
}

public void userRemove(String user){
    et_chat.append(user + " is now Offline.\n");
}

public class IncomingReader implements Runnable{
    @Override
    public void run(){
        String[] data;
        String stream, done = "Done", connect = "Connect", disconnect = "Disconnect", chat = "Chat", shutdown = "Shutdown";

        try{
            while ((stream = in.readLine()) != null){
                 data = stream.split(":");

                 if(data[data.length-1].equals(shutdown)){ 
                    if(data[0].equals("Server")){
                        et_chat.append("Server: The Server is Shutting down!\n");
                    }
                    sendDisconnect();
                    Disconnect();
                 }else if (data[data.length-1].equals(chat)){
                    et_chat.append(data[0] + ": " + extract(stream) + "\n");
                   // et_chat.setCaretPosition(et_chat.getDocument().getLength());
                 }else if (data[data.length-1].equals(connect)){
                    userAdd(data[0]);
                 }else if (data[data.length-1].equals(disconnect)){
                     userRemove(data[0]);
                 }else if (data[data.length-1].equals(done)){
                    users.clear();
                 }
            }
       }catch(Exception ex){ 

       }
    }

    private String extract(String input) {
        for(int i=0;i<input.length();i++){
            if(input.charAt(i) == ':'){
                input =  input.substring(i+1,input.length()-5);
                break;
            }
        } 
        return input;
    }
}


}  

My root_chat_server code:

import java.awt.EventQueue;
import java.io.*;
import java.net.*;
import java.util.*;

public class root_Chat_Server{
    private ServerStart serverStart;
    private boolean isStarted = false;
    private Thread starter;

@SuppressWarnings("rawtypes")
ArrayList clientOutputStreams;
@SuppressWarnings("rawtypes")
ArrayList clientHandler;
ArrayList<String> users;
/**
 * Create the application.
 */

 public class ClientHandler implements Runnable{
       BufferedReader reader;
       Socket sock;
       PrintWriter client;

       public ClientHandler(Socket clientSocket, PrintWriter user){
            client = user;
            try{
                sock = clientSocket;
                InputStreamReader isReader = new InputStreamReader(sock.getInputStream());
                reader = new BufferedReader(isReader);
            }
            catch (Exception ex){
                System.out.print("Unexpected error... \n");
            }
       }

       @Override
       public void run(){
            String message, connect = "Connect", disconnect = "Disconnect", chat = "Chat" ;
            String[] data;

            try{
                while ((message = reader.readLine()) != null){
                    System.out.print("Received: " + message + "\n");
                    data = message.split(":");

                    for (String token:data){
                        System.out.print(token + "\n");
                    }

                    if (data[data.length-1].equals(connect)){
                        tellEveryone((data[0] + ":" + data[1] + ":" + chat));
                        userAdd(data[0]);
                    }else if (data[data.length-1].equals(disconnect)){
                        tellEveryone((data[0] + ":has disconnected." + ":" + chat));
                        userRemove(data[0]);
                    }else if (data[data.length-1].equals(chat)){
                        System.out.print("\n\n"+ message +"\n\n");
                        tellEveryone(message);
                    }else{
                        System.out.print("No Conditions were met. \n");
                    }
                } 
             }catch (Exception ex){
                System.out.print("Lost a connection. \n");
                ex.printStackTrace();
                clientOutputStreams.remove(client);
             } 
       }
       public void stop() throws IOException{
           sock.close();
       }
 }

public root_Chat_Server() {

}

private void start(){
    if(!isStarted){
        starter = new Thread(serverStart = new ServerStart());
        starter.start();

        System.out.print("Server started...\n");
        isStarted = true;
    }
}


private void stop(){
    try{
        tellEveryone("Server:Shutdown");
        Thread.sleep(2000);
        serverStart.stop();
        isStarted = false;
    }catch (InterruptedException | IOException ex){
        Thread.currentThread().interrupt();
    }
    System.out.print("Server is stopping...\n\n\n");
}

private void users(){
    System.out.print("\nOnline Users:\n");

    for(String current_users : users){
        System.out.print("-" + current_users + "\n");
    }
}

public class ServerStart implements Runnable{
    ServerSocket serverSock;
    Socket clientSock;
    @SuppressWarnings({ "rawtypes", "unchecked" })
    @Override
    public void run(){
        clientOutputStreams = new ArrayList();
        users = new ArrayList();  
        clientHandler = new ArrayList();
        ClientHandler clientHand;

        try{
            serverSock = new ServerSocket(2222);

            while (true){
                clientSock = serverSock.accept();
                PrintWriter writer = new PrintWriter(clientSock.getOutputStream());
                clientOutputStreams.add(writer);

                Thread listener = new Thread(clientHand = new ClientHandler(clientSock, writer));
                clientHandler.add(clientHand);
                listener.start();
                System.out.print("Got a connection. \n");
            }
        }catch (Exception ex){
            System.out.print("Error making a connection. \n");
        }
    }

    private void stop() throws IOException{
        if(serverSock != null && clientSock != null){
            serverSock.close();
            clientSock.close();
        }else if(serverSock != null){
            serverSock.close();
        }
    }
}

public void userAdd (String data){
    String message, add = ": :Connect", done = "Server: :Done", name = data;
    if(!users.contains(name)){
        System.out.print("Before " + name + " added. \n");
        users.add(name);
        System.out.print("After " + name + " added. \n");
        String[] tempList = new String[(users.size())];
        users.toArray(tempList);

        for (String token:tempList){
            message = (token + add);
            tellEveryone(message);
        }
        tellEveryone(done);
    }else{
        PrintWriter writer = (PrintWriter)clientOutputStreams.get(clientOutputStreams.size()-1);
        ClientHandler clientHand = (ClientHandler)clientHandler.get(clientHandler.size()-1);
        writer.println("Disconnect:Shutdown");
        writer.flush();
        try {
            clientHand.stop();
        } catch (IOException e) {
            e.printStackTrace();
        }
        clientHandler.remove(clientHandler.size()-1);
        clientOutputStreams.remove(clientOutputStreams.size()-1);
    }
}

public void userRemove (String data){
    String message, add = ": :Connect", done = "Server: :Done", name = data;
    users.remove(name);
    String[] tempList = new String[(users.size())];
    users.toArray(tempList);

    for (String token:tempList){
        message = (token + add);
        tellEveryone(message);
    }
    tellEveryone(done);
}

@SuppressWarnings("rawtypes")
public void tellEveryone(String message){
Iterator it = clientOutputStreams.iterator();

    while (it.hasNext()){
        try{
            PrintWriter writer = (PrintWriter) it.next();
            writer.println(message);
            System.out.print("Sending: " + message + "\n");
            writer.flush();
        }catch (Exception ex){
            System.out.print("Error telling everyone. \n");
        }
    } 
}

/**
 * Launch the application.
 */
public static void main(String[] args){
    EventQueue.invokeLater(new Runnable(){
        public void run(){
            if(args.length == 1){
                root_Chat_Server server = new root_Chat_Server();
                if(args[0].equals("start")){
                    server.start();
                }else if(args[0].equals("stop")){
                    server.stop();
                }else if(args[0].equals("users")){
                    server.users();
                }
            }else{
                System.out.println("java root_Chat_Server start|stop|users");
            }
        }
    });
}
}

Thank you for every answer!

Answer 1

If you having trouble using native asynchronous in your project. Have a look this link. You can used this for your project. It runs on a backend Node.js with a android client.

Answer 2

There are no errors because you are catching exceptions and printing "Cannot connect to the Server! Try again!". You should print the exception messages to discover what is happening.

In Android, you have to run asynchronous network operations on a thread other than the main one. You are currently running the socket operation on the main thread, and this will cause an exception.