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why it says that there is no line in the clients InputStream?(socket programming)

I tried to write a simple program that runs a server and then accepts two clients. Then one of them tries to send a string to another client.
but my code doesn't work and I don't know why.
This is my TestClient class:
public class TestClient extends Thread{
int id;
String Name;
Socket client;
boolean isAsk;
public TestClient(int id,String clientName,boolean isAsk) throws IOException {
this.id=id;
this.Name=clientName;
this.isAsk=isAsk;
}
public void connectTheClientToTheLocalHost(ServerSocket server){
try {
client = new Socket("localhost",1111);
server.accept();
} catch (IOException e) {
e.printStackTrace();
}
}
public void readFromTerminal(){
try {
InputStream is=client.getInputStream();
OutputStream os = client.getOutputStream();
PrintWriter pw = new PrintWriter(os);
pw.println("sdklfsdklfk");
pw.flush();
pw.close();
}catch (IOException e){
e.printStackTrace();
}
}
public void closeTheCientSocket(){
try {
client.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public void write(){
try {
Scanner sc = new Scanner(client.getInputStream());
BufferedWriter bw = new BufferedWriter(new FileWriter(new File("file1.txt")));
String st =sc.nextLine();
bw.write(st);
bw.close();
}catch (IOException e){
e.printStackTrace();
}
}
#Override
public void run() {
if(isAsk){
readFromTerminal();
}
else{
write();
}
}
and this is the main function:
public class PCServer {
public static void main(String[] args){
try {
ServerSocket s = new ServerSocket(1111);
TestClient t1=(new TestClient(1,"reza",true));
TestClient t2=(new TestClient(2,"man",false));
t1.connectTheClientToTheLocalHost(s);
t1.start();
Scanner sc = new Scanner(t1.client.getInputStream());
String st=sc.nextLine();
System.out.println(st);
t1.closeTheCientSocket();
t2.connectTheClientToTheLocalHost(s);
PrintWriter pw = new PrintWriter(t2.client.getOutputStream());
pw.println(st);
pw.flush();
t2.start();
t2.closeTheCientSocket();
}catch (Exception e){
e.printStackTrace();
}
}
}
actually this code returns an exception in
String st=sc.nextLine();
in main function and says that there is no line found.
what is the problem?

ServerSocket in java usually used in another way.
If you need point-to-point connection, one host creates a ServerSocket and accepts connections. Examples:
First host example:
try(ServerSocket serverSocket = new ServerSocket(5555);
Socket socket = serverSocket.accept();
// it more convenient to use DataInputStream instead of Scanner I think
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());) {
while (!Thread.currentThread().isInterrupted()) {
String msg = dataInputStream.readUTF();
System.out.println("got request: " + msg);
dataOutputStream.writeUTF("1-response");
dataOutputStream.flush();
}
} catch (IOException e) {
e.printStackTrace();
}
Second host example:
try(Socket socket = new Socket("127.0.0.1", 5555);
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream())) {
while (!Thread.currentThread().isInterrupted()) {
dataOutputStream.writeUTF("2-request");
dataOutputStream.flush();
String msg = dataInputStream.readUTF();
System.out.println("got response: " + msg);
}
} catch (IOException e) {
e.printStackTrace();
}
If you want one host talk to another over the server (broker), then you need plane java Sockets on hosts and ServerSocket on broker, and broker must transmit messages it received from one host to another. Examples:
Broker (run it in separate thread or process)
try {
List<Socket> sockets = new ArrayList<>();
ServerSocket serverSocket = new ServerSocket(5555);
// accepting connections from 2 clients
for (int i = 0; i < 2; i++) {
Socket socket = serverSocket.accept();
sockets.add(socket);
}
// streams for first host
InputStream hostOneInputStream = sockets.get(0).getInputStream();
DataInputStream hostOneDataInputStream = new DataInputStream(sockets.get(0).getInputStream());
DataOutputStream hostOneDataOutputStream = new DataOutputStream(sockets.get(0).getOutputStream());
// streams for second host
InputStream hostTwoInputStream = sockets.get(1).getInputStream();
DataInputStream hostTwoDataInputStream = new DataInputStream(sockets.get(1).getInputStream());
DataOutputStream hostTwoDataOutputStream = new DataOutputStream(sockets.get(1).getOutputStream());
while (!Thread.currentThread().isInterrupted()) {
if (hostOneInputStream.available() > 0) {
String msg = hostOneDataInputStream.readUTF();
System.out.println("got message from host 1: " + msg);
hostTwoDataOutputStream.writeUTF(msg);
hostTwoDataOutputStream.flush();
System.out.println("message " + msg + " sent to host two");
}
if (hostTwoInputStream.available() > 0) {
String msg = hostTwoDataInputStream.readUTF();
System.out.println("got message from host 2: " + msg);
hostOneDataOutputStream.writeUTF(msg);
hostOneDataOutputStream.flush();
System.out.println("message " + msg + " sent to host one");
}
}
} catch (IOException e) {
e.printStackTrace();
}
First host (run it in separate thread or process)
try(Socket socket = new Socket("127.0.0.1", 5555);
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream())) {
while (!Thread.currentThread().isInterrupted()) {
dataOutputStream.writeUTF("1");
dataOutputStream.flush();
String msg = dataInputStream.readUTF();
System.out.println("got msg: " + msg);
TimeUnit.SECONDS.sleep(5);
}
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}
Second host (run it in separate thread or process)
try(Socket socket = new Socket("127.0.0.1", 5555);
DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream())) {
while (!Thread.currentThread().isInterrupted()) {
String msg = dataInputStream.readUTF();
System.out.println("got msg: " + msg);
TimeUnit.SECONDS.sleep(5);
dataOutputStream.writeUTF("2");
dataOutputStream.flush();
}
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}

sending and recieving data through sockets in the same activity

i'm using TCP socket to send and receive data from the same socket in the same activity through client server thread, the purpose of that is to send a string to other device and that string will trigger a notification once the other device receives it then that device will replay with something like dismiss or accepted, the problem that i'm having is after sending the string the other device receives it and send the dismiss or accepted String but my divice doesn't receive that string i guess there is a problem in my ServerThread be aware that the server thread and client thread are in the same activity used as an inner classes and get called in a button.
code:
ClientThread
private class ChatClientThread extends Thread {
#Override
public void run() {
Socket socket = null;
DataOutputStream dataOutputStream = null;
try {
socket = new Socket("192.168.0.113", 23);
dataOutputStream = new DataOutputStream(
socket.getOutputStream());
dataOutputStream.writeUTF(" "+"SolveProblemOrder_2");
dataOutputStream.flush();
ServerThread serv =new ServerThread();
serv.start();
} catch (UnknownHostException e) {
e.printStackTrace();
final String eString = e.toString();
TicketDetails.this.runOnUiThread(new Runnable() {
#Override
public void run() {
Toast.makeText(TicketDetails.this, eString, Toast.LENGTH_LONG).show();
}
});
} catch (IOException e) {
e.printStackTrace();
final String eString = e.toString();
TicketDetails.this.runOnUiThread(new Runnable() {
#Override
public void run() {
Toast.makeText(TicketDetails.this, eString, Toast.LENGTH_LONG).show();
}
});
} 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();
}
}
TicketDetails.this.runOnUiThread(new Runnable() {
#Override
public void run() {
}
});
}
}
}
ServerThread
public class ServerThread extends Thread {
private ServerSocket serverSocket;
private Socket clientSocket;
public void run(){
try{
// Open a server socket listening on port 23
InetAddress addr = InetAddress.getByName(getLocalIpAddress());
serverSocket = new ServerSocket(23, 0,addr);
try{
clientSocket = serverSocket.accept();
DataInputStream dataInputStream = new DataInputStream(clientSocket.getInputStream());
String newMsg = null;
Toast.makeText(getApplicationContext(), newMsg, Toast.LENGTH_LONG).show();
// Client established connection.
// Create input and output streams
while (true) {
if (dataInputStream.available() > 0) {
newMsg = dataInputStream.readUTF();
}
}}catch(Exception e){
e.printStackTrace();
}
// Perform cleanup
} catch(Exception e) {
// Omitting exception handling for clarity
}
}
private String getLocalIpAddress() throws Exception {
String resultIpv6 = "";
String resultIpv4 = "";
for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces();
en.hasMoreElements();) {
NetworkInterface intf = en.nextElement();
for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses();
enumIpAddr.hasMoreElements();) {
InetAddress inetAddress = enumIpAddr.nextElement();
if(!inetAddress.isLoopbackAddress()){
if (inetAddress instanceof Inet4Address) {
resultIpv4 = inetAddress.getHostAddress().toString();
} else if (inetAddress instanceof Inet6Address) {
resultIpv6 = inetAddress.getHostAddress().toString();
}
}
}
}
return ((resultIpv4.length() > 0) ? resultIpv4 : resultIpv6);
}
}
i start those two threads in a button Click listener:
ChatClientThread chatClient=new ChatClientThread();
chatClient.start();
ServerThread serv =new ServerThread();
serv.start();
if this won't work using server/client in the same activity using the same port is there any other way to listen to a socket like is there a built in listener or something like that.
any help is appreciated

You write to socket thru socket.getOutputStream() and you must read from InputStream of socket.getInputStream() ;
You can adapt your code .
Your server use InputStream from socket to read data ,so you must to do also in your client code , cause you want also to receive data not only to send.
check this out just read is is very simple.
https://systembash.com/a-simple-java-tcp-server-and-tcp-client/
See the code for reading from socket taht start with :
BufferedReader inFromClient =
new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
and code for writing to socket:
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
or search google : java client server .
The ideea is that you send data to the socket outputstream and you can read it from same socket inputstream.
you see here example it read data from socket input and send data thru socket output , to server
String sentence;
String modifiedSentence;
BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
Socket clientSocket = new Socket("localhost", 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + '\n');
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close();

android.os.NetworkOnMainThreadException (client application android / serveur application java) (send string)(using emulator localhost) [duplicate]

This question already has answers here:
How can I fix 'android.os.NetworkOnMainThreadException'?
(66 answers)
Closed 7 years ago.
the class of client in android application (using emulator localhost), sending a string to my java application (serveur) :
public class Client_socket extends MainActivity{
private static Socket socket;
public static void lance()
{
try
{
String host = "localhost";
int port = 25000;
InetAddress address = InetAddress.getByName(host);
socket = new Socket("127.0.0.3", port);
//Send the message to the server
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
String nom = "premiere";
String sendMessage = ism + "\n";
bw.write(sendMessage);
bw.flush();
System.out.println("Message sent to the server : "+sendMessage);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " +message);
}
catch (Exception exception)
{
exception.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
}
the class of serveur in java application how recive my string :
what the ip and port can i use?, and how can i get my ip?
public class Server
{
private static Socket socket;
public static void main(String[] args)
{
try
{
int port = 25000;
ServerSocket serverSocket = new ServerSocket(port);
System.out.println("Server Started and listening to the port 25000");
//Server is running always. This is done using this while(true) loop
while(true)
{
//Reading the message from the client
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String nom = br.readLine();
System.out.println("Message received from client is "+nom);
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
try
{
socket.close();
}
catch(Exception e){}
}
}
}

Make sure you execute network operations in a background thread:
new Thread(new Runnable() {
#Override
public void run() {
lance(); // call your network method here
}
}).start();

Java TCP socket accept stops running code

I have some (incomplete) code here for a client/server pair, here is the server class, but for some reason unknown to me the code appears to stop running anything below the serverSocket.accept()
What am I doing wrong?
Thanks
class MPTagServer{
public String serverName = "MPTag Server";
public int gSize = 16;
public int maxPlayers = 16;
ServerSocket serverSocket = null;
Socket clientSocket = null;
PrintWriter out = null;
BufferedReader in = null;
MPTagServer(String sn, int gs, int mp){
serverName = sn;
gSize = gs;
maxPlayers = mp;
}
public void start() throws Exception{
Task serverTask = new Task<Void>(){
#Override protected Void call() throws Exception{
int port = 6789;
try{
serverSocket = new ServerSocket(port);
}
catch(IOException e){
System.err.println("Could not listen on port: " + port);
System.exit(1);
}
try{
System.out.println("This will print");
clientSocket = serverSocket.accept(); //Code won't run below here
System.out.println("This won't print");
}
catch(IOException e){
System.err.println("Accept failed.");
System.exit(1);
}
out = new PrintWriter(clientSocket.getOutputStream(), true);
in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
String inputLine, outputLine;
ComProtocol cp = new ComProtocol();
outputLine = cp.init();
out.println(outputLine);
out.close();
in.close();
clientSocket.close();
serverSocket.close();
return null;
}
};
Thread serverThread = new Thread(serverTask);
serverThread.setDaemon(true);
serverThread.start();
}
}

ServerSocket.accept() blocks until a connection is made to the socket. See http://docs.oracle.com/javase/6/docs/api/java/net/ServerSocket.html#accept(). When a client connects to your socket, the socket will unblock, and you should see "This won't print".

BufferedWriter.write() does not seem to work

I have two Java applications, where an Android client connects to a server on a computer and sends a message using BufferedWriter over websockets.
The client:
try {
toast("Sending...");
Socket sock = new Socket(ip, PORT);
OutputStream os = sock.getOutputStream();
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
bw.flush();
bw.write("Hello Server!");
toast("Connected!");
} catch (UnknownHostException e) {
toast(e.getMessage());
} catch (IOException e) {
toast(e.getMessage());
}
The server:
public static void main(String[] args) {
ServerSocket server;
ConnectionThread ct;
Socket s;
ExecutorService es = Executors.newSingleThreadExecutor();
try {
System.out.println("Starting server...");
server = new ServerSocket(1337);
s = server.accept();
ct = new ConnectionThread(s);
es.execute(ct);
} catch (IOException ex) {
ex.printStackTrace();
}
}
The ConnectionThread class:
public class ConnectionThread implements Runnable {
private Socket sock;
private InputStream is;
private BufferedReader br;
private boolean online;
public ConnectionThread(Socket s) {
System.out.println("Creating connection thread.");
this.sock = s;
online = true;
}
#Override
public void run() {
String input = "";
try {
System.out.println("Starting to read...");
is = sock.getInputStream();
br = new BufferedReader(new InputStreamReader(is));
while (online) {
input = br.readLine();
if(input != null){
System.out.print("Received message: ");
System.out.println(input);
}
}
br.close();
is.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
When I run the server, and then the client, the client will show the "Connected!" toast, and the server's output will be:
Starting server...
Creating connection thread.
Starting to read...
So, it seems like the connection is actually being made, but the message does not arrive. Does anybody know why this could be happening?

Your server is expecting a complete line terminated by a newline. Try:
bw.write("Hello Server!");
bw.newLine();

Do it like this...
String s = new String();
while ((br.readLine())!=null) {
s = s+br.readLine();
System.out.print("Received message: ");
System.out.println(input);
}
}
And
bw.println("Hello Server");

I notice that you don't send an endline on your client, so the BufferedReader.readline() will never return, because it cannot match the \n-character. Try it again with
bw.write("Hello Server!\n");
on the client side.