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Java cannot read and write to socket at the same time

I am trying to build a simple multi client chat application using java sockets. The way I have gone about doing this is by having a client class that connects to a server class that waits for clients to connect and creates a new thread to deal with that client(Where the socket connection is read and written to). The client also reads from and writes to the socket connection to this thread. However, when the client wrote to the output stream of the socket, the server would not respond. A similar question here was posted:
Can you write to a sockets input and output stream at the same time?
One of the answers here says that you can read and write to a socket at the same time as long as reading from the socket is done on a separate thread.
Here is my client application:
public class Client {
Socket socket;
public static void main(String[] args) {
new Client();
}
public Client() {
try {
socket = new Socket("localhost", 4444);
new Thread() {
#Override
public void run() { //read from the input stream
try(
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
) {
String line;
while( (line = in.readLine()) != null ) {
System.out.println("Server said: " + line);
}
} catch(IOException e) {
}
}
}.start();
//write to output stream
try(
PrintWriter out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
Scanner userInput = new Scanner(System.in);
){
System.out.println("Enter Something: ");
if(userInput.hasNextLine()) {
out.println(userInput.nextLine());
}
} catch (IOException e) {
}
} catch(IOException e) {
}
}
}
And my server application:
public class Server {
ServerSocket ss;
public static void main(String[] args) {
new Server();
}
public Server() {
System.out.println("Server Running...");
try {
ss = new ServerSocket(4444);
while(true) {
Socket socket = ss.accept();
new Thread() { //create new thread connection to client
#Override
public void run() {
new Thread() { //thread that reads inputstream
#Override
public void run() {
try(
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
) {
String line;
while( (line = in.readLine()) != null ) {
System.out.println("Client said: " + line);
//The problem seems to lie here.
}
} catch(IOException e) {
}
}
}.start();
//write to outputstream
try (
PrintWriter out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
) {
String sendToClient = "Hey, my name is Server007 B)";
out.println(sendToClient);
} catch(IOException e) {
}
}
}.start();
}
} catch (IOException e) {}
}
}
I will run the server, then run the client, on the client side the output is
Server said: Hey, my name is Server007
Enter something:
Hello! <- enter anything
but the server does not print 'Client said: Hello!' like I expected it to. I hope I made my problem clear enough, thanks.

Ok, so I figured it out, I will answer my own question in case anyone makes the same mistake. The PrintWriter constructor should be this:
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
Not this:
PrintWriter out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
Alternatively, I could have done this:
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
I must have just gotten confused between BufferedWriter and PrintWriter :P

Java Check if socket sends

I am creating a simple Java program where the client sends a message to the server and the server replies back with a confirmation message. But my question is: Can I get the server response/broadcast before the BufferedReader line?
Server:
public class Multithread extends Thread{
Socket sock;
static ArrayList<Multithread> clientList = new ArrayList<Multithread>();
public Multithread(Socket sock){
this.sock = sock;
}
public void run(){
try{
DataInputStream in = new DataInputStream(this.sock.getInputStream());
String read = in.readUTF();
if(read.equalsIgnoreCase("exit")){
System.out.println(this.sock.getRemoteSocketAddress()+" just dced");
clientList.remove(this);
this.sock.close();
}
else{
String said = this.sock.getRemoteSocketAddress() +" said "+read;
System.out.println(said);
for(Multithread multi : clientList){
DataOutputStream o = new DataOutputStream(multi.sock.getOutputStream());
o.writeUTF(said);
}
this.sock.close();}
}catch(IOException e){
}
}
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = new ServerSocket(7777);
System.out.println("Listening");
while(true){
Socket socket = serverSocket.accept();
System.out.println("Connected to "+socket.getRemoteSocketAddress());
Multithread multi = new Multithread(socket);
clientList.add(multi);
multi.start();
}
}
}
Client:
public class Clients{
public static void main(String[] args) throws UnknownHostException, IOException {
while(true){
Socket socket = new Socket("localhost",7777);
DataInputStream in = new DataInputStream(socket.getInputStream());
DataOutputStream out = new DataOutputStream(socket.getOutputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String line = br.readLine();
out.writeUTF(line);
if(line.equalsIgnoreCase("exit"))
{
System.out.println("Disconnected");
socket.close();
break;
}
else{
System.out.println("Server said :"+in.readUTF());
socket.close();
}
}
}
}

Sending Strings through Sockets

Here is the Server
public class SocketMsg {
public static void main(String[] args) throws IOException{
ServerSocket ss = new ServerSocket("number goes here");
System.out.println("Server Ready");
ss.accept();
}
}
Client:
public class SocketMesg {
public static void main(String[] args) throws IOException{
Socket socket = null;
OutputStreamWriter osw;
String str = "Hello World";
try {
socket = new Socket("localhost", "number goes here");
osw =new OutputStreamWriter(socket.getOutputStream());
osw.write(str, 0, str.length());
} catch (IOException e) {
System.err.print(e);
}
finally {
socket.close();
}
}
Personally, the code works but the strings are not sending to the other host, I gave them the same number, but it is not working. The client is sending it back to the server on the DOS window. Did I make a error? What did I do wrong?

Your server-side at least needs the following.
Socket clientSocket = serverSocket.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null) {
// process inputLine;
}

You need to flush outputstream to commit write buffer to the socket. Also be careful with charset if writing strings. This example explicitly uses UTF-8 through "low level" byte array buffer. I think you are practicing your first socket programming so I kept this very simple.
Server.java
import java.net.*;
import java.io.*;
public class Server {
public static void main(String[] args) throws Exception {
ServerSocket ss = new ServerSocket(1122);
System.out.println("Server Ready");
while(true) {
Socket socket = ss.accept();
InputStream is = socket.getInputStream();
// client must send 1-10 bytes, no more in single command
byte[] buf = new byte[10];
int read = is.read(buf, 0, buf.length);
String cmd = new String(buf, 0, read, "UTF-8");
System.out.println(cmd);
socket.close(); // we are done, this example reads input and then closes socket
}
}
}
Client.java
import java.net.*;
import java.io.*;
public class Client {
public static void main(String[] args) throws Exception {
Socket socket = null;
// send max of 10 bytes to simplify this example
String str = "ABCDEFGHIJ";
try {
socket = new Socket("localhost", 1122);
OutputStream os = socket.getOutputStream();
byte[] buf = str.getBytes("UTF-8");
os.write(buf, 0, buf.length);
os.flush();
} catch (IOException ex) {
System.err.print(ex);
} finally {
socket.close();
}
}
}

simple client - server talking to each other classes in Java

I am trying to figure out why I can send messages to the client from the server but when I try the other way around (to send messages from the client to the server) the program halts like it is waiting for some action to happen.
also how to prevent the sockets from being closed immediately.
this is the code:
Client Class
import java.io.*;
import java.net.*;
public class Client {
public static void main(String[] args) {
Client aClient = new Client();
aClient.run();
}
private Socket socket;
private PrintWriter toServer;
private BufferedReader fromServer;
public void run() {
try {
socket = new Socket("localhost", 9000);
if (socket.isConnected()){
System.out.println("CONNECTED");
}
fromServer = new BufferedReader(new InputStreamReader(socket.getInputStream()));
toServer = new PrintWriter(socket.getOutputStream());
toServer.print("hello server");
System.out.print(fromServer.readLine());
toServer.close();
socket.close();
} catch (Exception error) {
System.out.println("CLIENT ERROR: " + error);
}
}
}
Server Class
import java.io.*;
import java.net*;
public class Server {
public static void main(String[] args) {
Server aServer = new Server();
aServer.run();
}
private ServerSocket mainSocket;
private Socket socket;
private PrintWriter toClient;
private BufferedReader fromClient;
public Server(){
try{
mainSocket = new ServerSocket(9000);
}
catch (Exception error){
System.out.print("Error :"+error);
}
}
public void run() {
System.out.println("WAITING FOR CLIENTS");
try {
socket = mainSocket.accept();
if(socket.isConnected()) {
System.out.println("CONNECTED.");
}
fromClient = new BufferedReader(new InputStreamReader(socket.getInputStream()));
toClient = new PrintWriter(socket.getOutputStream());
System.out.println(fromClient.readLine());
toClient.print("hello Client");
toClient.close();
}
catch (Exception error) {
System.out.println("SERVER ERROR :" + error);
}
}
}

Add this before toServer.print("hello server"); to Client class. Its read from System.in and send to the Server class:
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromUser;
while((fromUser = stdIn.readLine()) != null) {
System.out.println("Client: " + fromUser);
toServer.println(fromUser);
}
And to Server class add this, before System.out.println(fromClient.readLine());, its read line from client and print to System.out:
String inputLineFromClient;
while ((inputLineFromClient = fromClient.readLine()) != null) {
System.out.println(inputLine);
}
Socket not closing before you invoke method close() or occurs some Exception.

your server is not reading anything.
use
fromClient.readLine();

send from client to server and from server to client in java

I develop code to send form client to server then the server has to send what it receives from client again to client. but in my code the server only receives the message but does not resend it again. I do not know what is the problem
This is my client code
public class Client implements Runnable{
private static Socket s = null;
//private static BufferedOutputStream fromUser = null;
private static DataInputStream fromServer = null;
private static InputStreamReader input = new InputStreamReader(System.in);
private static InputStreamReader inputstreamreader = null;
private static BufferedReader bufferedreader = null;
private static DataOutputStream fromUser = null;
private static int chara = 0;
private static String line = null;
static int port = 0;
static String host = null;
//connect to server
#Override
public void run() {
try {
inputstreamreader = new InputStreamReader(s.getInputStream());
bufferedreader = new BufferedReader(inputstreamreader);
//charr = fromClient.read();
while(true){
if ((line = bufferedreader.readLine()) != null){
System.out.println(line);}
if(line.equals(-1)){
break;
}
}//end while
}catch(NullPointerException e) {
// do something other
}
catch (IOException e) {
System.out.println(e);
}
}//end the run
//constructor with two arguments
public Client(String host, int port){
try{
s = new Socket (host,port);
}
catch(Exception e){}
}
//send message to from Client to Server
public static void sendToServer(){
try{
fromUser =new DataOutputStream (new BufferedOutputStream(s.getOutputStream()));
chara =input.read();
while(true){
if (chara == '~'){
break;}
fromUser.write(chara);
fromUser.flush();
chara =input.read();
}//end while
}
catch (IOException e) {
System.out.println(e);
}
}//end send message
I tried to use thread to receive message but also does not work. I tried without thread it does not work too.
public static void main(String [] args){
host = args[0];
port = Integer.parseInt(args[1]);
System.out.println("Start connection .....");
Client client = new Client(host,port);
Thread thread = new Thread(client);
thread.start();
//connect(host,port);
client.sendToServer();
client.close();
}//end main
and this is my server code
public class Server extends Thread{
private static Socket s = null;
private static ServerSocket ss = null;
private static DataOutputStream fromUser = null;
private static DataInputStream fromClient = null;
private static InputStreamReader input = new InputStreamReader(System.in);
private static InputStreamReader inputstreamreader = null;
private static BufferedReader bufferedreader = null;
static String line=null;
static String sendC;
private static int chara = 0;
static int port = 0;
//connect to server
static void connect(int port){
try{
ss = new ServerSocket (port);
System.out.println("Listening on port "+port+"...");
s = ss.accept();
System.out.println("Has been connected .....");
}
catch (IOException e) {
System.out.println(e);
}
}//end of the connection method
//send message to from Client to Server
public static void sendToClient(String text){
try{
fromUser =new DataOutputStream (new BufferedOutputStream(s.getOutputStream()));
sendC =text;
fromUser.write(sendC.getBytes());
fromUser.flush();
}
catch (IOException e) {
System.out.println(e);
}
}//end send message
public static void receiveFromClient(){
try {
inputstreamreader = new InputStreamReader(s.getInputStream());
bufferedreader = new BufferedReader(inputstreamreader);
//charr = fromClient.read();
while(true){
if ((line = bufferedreader.readLine()) != null){
System.out.println(line);
sendToClient(line);}
if(line.equals(-1)){
break;
}
}//end while
}catch(NullPointerException e) {
// do something other
}
catch (IOException e) {
System.out.println(e);
}
}//end send message
this is main method for server
public static void main(String [] args){
port = Integer.parseInt(args[0]);
System.out.println("Start connection .....");
connect(port);
receiveFromClient();
//sendToClient();
close();
}//end main
I do not have alot of knowledge in java especially about the socket
thanks for your help

a simply search for a java echo server shows this
public class EchoServer {
public static void main(String[] args) throws Exception {
// create socket
int port = 4444;
ServerSocket serverSocket = new ServerSocket(port);
System.err.println("Started server on port " + port);
// repeatedly wait for connections, and process
while (true) {
// a "blocking" call which waits until a connection is requested
Socket clientSocket = serverSocket.accept();
System.err.println("Accepted connection from client");
// open up IO streams
In in = new In (clientSocket);
Out out = new Out(clientSocket);
// waits for data and reads it in until connection dies
// readLine() blocks until the server receives a new line from client
String s;
while ((s = in.readLine()) != null) {
out.println(s);
}
// close IO streams, then socket
System.err.println("Closing connection with client");
out.close();
in.close();
clientSocket.close();
}
}
}
see http://introcs.cs.princeton.edu/java/84network/EchoServer.java.html