Hi I am trying to implement server operating with multiply clients
The problem is that the server does not receive the message from inputstream and wait until it happen. if the client don't close the stream after writing to it the server will continue to wait. After the client send the message, he try to read from the inputstream waiting for response, but the server is waiting for the request. So.. deadlock
This is my client class
public class Client implements Runnable{
...
#Override
public void run() {
BufferedReader is = null;
BufferedWriter os = null;
try(Socket socket = new Socket(address.getHostName(), address.getPort());){
String request = String.format("%s-%d-%s",this.destination, this.desiredPlace, this.paymentMethod.toString());
os = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
is = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintWriter pw = new PrintWriter(os, true);
pw.write(request);
pw.flush();
// if I close the stream here the request will be send, but this will close the socket so the I will not receive response.
String response;
while ((response = is.readLine()) != null){
System.out.println(response);
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
And this is my server class
public void perform() throws IOException, DestionationProcessingException, InterruptedException {
try (ServerSocket server = new ServerSocket(port);) {
StandalonePayDesk offLinePayDesk = new StandalonePayDesk(ticketManager);
this.threadPool.submit(offLinePayDesk);
while (true) {
Socket socket = server.accept();
RequestHandler handler = new RequestHandler(this.threadPool, offLinePayDesk, this.ticketManager);
handler.process(socket);
}
}
}
and RequestHandler class for processing each client
try (BufferedReader reader = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintWriter writer = new PrintWriter(client.getOutputStream(), true)) {
writer.println("hello");
writer.flush();
String line;
while ((line = reader.readLine()) != null) {
String[] lineTokens = line.split("-");
...
Can anyone help me to solve this problem ?
pw.write(request);
Your client is writing a request but not a line. Your server is reading a line, with readLine(), and will block until the line terminator arrives, which is never, so it will never send a reply, so your client will never receive it, so it will block forever.
Change the above to:
pw.println(request);
Related
Can somebody explain to me what I am doing wrong.First time I try to implement TCP between Java and C#:
Sever code c#
`
public void CreateServer()
{
Thread thread = new Thread(() =>
{
IPAddress addr = IPAddress.Parse(localIP);
tcpListener = new TcpListener(addr, 5053);
if (tcpListener != null)
{
tcpListener.Start();
while (!end)
{
TcpClient tcpClient = tcpListener.AcceptTcpClient();
var ip = ((IPEndPoint)tcpClient.Client.RemoteEndPoint).Address.ToString();
Console.WriteLine("Client connected from "+ip);
NetworkStream clientStream = tcpClient.GetStream();
StreamReader reader = new StreamReader(clientStream, Encoding.UTF8);
try
{
string request = reader.ReadToEnd();
Console.WriteLine("Message from client: " + request);
Byte[] StringToSend = Encoding.UTF8.GetBytes("Server");
clientStream.Write(StringToSend, 0, StringToSend.Length);
Console.WriteLine("Sending response back");
}
catch (Exception e)
{
Console.WriteLine(e);
}
}
}
});
thread.Start();
}
`
Client code java
`
public class TCP {
private String IP;
private InetAddress server;
private Socket socket;
public TCP(String IP) {
this.IP = IP;
}
protected void runTCP() {
try {
server = InetAddress.getByName(IP);
socket = new Socket(server, 5053);
System.out.println("Client connected. Listening on port 5053");
} catch (Exception e) {
e.printStackTrace();
}
}
public void sendMessage(String message) {
try {
System.out.println("Sending data...");
if (socket.isClosed()) socket = new Socket(server, 5053);
PrintWriter writer = new PrintWriter(socket.getOutputStream());
writer.print(message);
writer.flush();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public void getResponseServer() {
Thread thread = new Thread() {
#Override
public void run() {
try {
System.out.println("Attempting to get response...");
if (socket.isClosed()) socket = new Socket(server, 5053);
BufferedReader mBufferIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String mServerMessage = mBufferIn.readLine();
System.out.println("Server message: " + mServerMessage);
} catch (Exception e) {e.printStackTrace();}
}
};
thread.start();
}
}
`
Output on server I get when sending "Hello" from client to server:
Client connected from 192.16.... Message from client: Hello Sending response back Client connected from 192.16....
Output on client:
Client connected. Listening on port 5053 Sending data... Attempting to get response...
Never gets response... Why?
Tried researching but found nothing yet, tried other code but didnt work aswell...
sorry , I can't comment. maybe you can use telnet command to vertify c# code is corrent.
telnet ip port
first, locate problem, then solve it.
if server is ok , we can use nc command vertify client code, I have test your java code , except every send data will close socket , other is ok.
Fixed it by removing writer.close() cause that causes socket closing and makes another connection to the server by creating again the socket which makes the server wait for a stream of data and the client wait for a response...
System.out.println("Sending data...");
PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
writer.println(message);
InputStream input = socket.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(input));
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
I have my server code below over here:
public void startServer() {
ServerSocket listener = selectUnusedPortFromRange(1024, 65535);
Thread t = new Thread(new Runnable() {
#Override
public void run() {
try {
String command = null;
while (true) {
Socket socket = listener.accept();
System.out.println("Got a connection from: " + socket.getLocalPort());
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
command = in.readLine();
System.out.println("GOT HERE"); //Not being printed out
if (command != null && !"".equals(command)) {
if ("connection".equals(command)) {
Writer writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
writer.write("success\n");
writer.flush();
}
}
}
}
}
}
t.start();
}
This is my client side:
public void makeConnection() {
try {
Socket socket = new Socket(IP, PORT);
Writer writer = new PrintWriter(socket.getOutputStream(), true);
writer.write("connection\n");
BufferedReader socketRead = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String str;
while ((str = socketRead.readLine()) != null) {
if ("success".equals(str)) {
System.out.println("Successfully saved all hosts to: " + listOfHosts.get(i));
socketRead.close();
socket.close();
iStream.close();
writer.close();
}
}
}catch (Exception e) {
System.out.println(e.getMessage());
}
}
On the client side after I create my socket to the connect to the server I write "connection" into the outputStream of the socket and wait for an acknowledgement back from the server saying success. For some reason the connection is not being made to the server. In the server System.out.println("Got a connection from: " + socket.getLocalPort()); this line is not being printed out.
Is there something wrong that I am doing. I can't spot it. And I am not getting an exception thrown when I try to connect to my server.
1) Make sure you use the same port for both the Client and Server. They must communicate over the same port. It seems you may be using different ports currently.
2) Make sure you actually start your server thread. As-is in your code above, you make a new Thread, but never start it. t.start() must be called somewhere.
3) If this is on your local machine, you may be better off using localhost instead of the actual IP address. Firewalls might treat your external IP differently.
4) Terminate your messages with a newline character, such as \n, so that your BufferedReader can use it's readLine() method. For good measure, also follow-up by flushing the writer's buffer, just in case the newline character didn't trigger that. writer.flush();
And lastly, make sure you terminate the JVM before trying to run your code again. Your code has not shutdown mechanism to un-bind the server from the port... so you may get an exception thrown telling you the port and/or address are already in use. If that happens, either change ports, or kill the java process running in the background.
Here is your code, slightly modified to run on my system. It's working as you might expect it to. I tried to change as little as possible just to get it working on my system. One note is, I hard-coded the port number into the server and client - that's not required, it was just convenient for me to test with:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.Writer;
import java.net.ServerSocket;
import java.net.Socket;
public class Test {
public static void main(String[] args) throws IOException {
Test test = new Test();
test.startServer();
test.makeConnection();
}
public void startServer() throws IOException {
final ServerSocket listener = new ServerSocket(60001);
Thread t = new Thread(new Runnable() {
#Override
public void run() {
try {
String command = null;
while (true) {
Socket socket = listener.accept();
System.out.println("Got a connection from: " + socket.getLocalPort());
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
command = in.readLine();
System.out.println("GOT HERE");
if (command != null && !"".equals(command)) {
if ("connection".equals(command)) {
Writer writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
writer.write("success\n");
writer.flush();
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
});
t.start();
}
public void makeConnection() {
System.out.println("Making Connection");;
try {
Socket socket = new Socket("localhost", 60001);
Writer writer = new PrintWriter(socket.getOutputStream(), true);
writer.write("connection\n");
writer.flush();
BufferedReader socketRead = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String str;
while ((str = socketRead.readLine()) != null) {
if ("success".equals(str)) {
System.out.println("Successfully saved all hosts to: "); //+ listOfHosts.get(i));
socketRead.close();
socket.close();
//iStream.close();
writer.close();
}
}
}catch (Exception e) {
System.out.println(e.getMessage());
}
}
}
I was facing the exact same issue. I overcame it by using an ACK mechanism (Wasn't my idea, it was suggested to me). The idea is that client would make a request to server and keep the socket connection alive (and the ouput stream open) till server responds back an agreed ACK message over the same channel. Once the client receives the ACK message, only then it would close the connection.
Below is the code for Server :-
final ServerSocket listener = new ServerSocket(11111);
Thread t = new Thread(new Runnable() {
#Override
public void run() {
try {
String command = null;
while (true) {
System.out.println("About to accept");
Socket socket = listener.accept();
System.out.println("Got a connection from: " + socket.getLocalPort());
DataInputStream inputStream = new DataInputStream(socket.getInputStream());
StringBuilder str = new StringBuilder(inputStream.readUTF());
//command = in.readLine();
System.out.println("GOT HERE. Msg received : "+str);
if (str != null && !"".equals(str.toString())) {
command = str.toString();
if ("connection".equals(command)) {
System.out.println("Got connection message");
DataOutputStream outputStream = new DataOutputStream(socket.getOutputStream());
outputStream.writeUTF("connection");
outputStream.close();
}
}
inputStream.close();
System.out.println("Done");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
}
}
});
t.start();
}
Client :-
public void makeConnection() {
try {
System.out.println("In makeConnection");
Socket socket = new Socket("127.0.0.1", 11111);
DataOutputStream outputStream = new DataOutputStream(socket.getOutputStream());
outputStream.writeUTF("connection");
InputStream inputStream = socket.getInputStream();
DataInputStream dataInputStream = new DataInputStream(inputStream);
StringBuilder str;
do {
str = new StringBuilder(dataInputStream.readUTF());
} while (!str.toString().equals("connection"));
System.out.println("Successfully saved all hosts to: ");
outputStream.close();
dataInputStream.close();
socket.close();
outputStream.close();
}catch (Exception e) {
System.out.println(e.getMessage());
}
}
A call to start the proceedings :-
public void start() throws IOException, InterruptedException {
System.out.println("Starting server");
startServer();
Thread.sleep(1000);
System.out.println("Starting connection");
makeConnection();
}
I want to write a client-sever program in which server and client send messages to each other. First, my server send a message to client, then the client reply. Next, my server send another message, the client reply. The problem is, on my first message induced by the server, the client does not respond.
My server:
public class Server {
public void go() {
try {
ServerSocket serverSocket = new ServerSocket(9999);
System.out.println("Server listening ...");
Socket socket = serverSocket.accept();
try (
PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
) {
String input;
printWriter.println(new Scanner(System.in).nextLine());
while ((input = bufferedReader.readLine()) != null) {
System.out.println(input);
printWriter.println(new Scanner(System.in).nextLine());
if(input == "Bye") break;
}
}
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
public static void main(String[] args) {
Server server = new Server();
server.go();
}
}
My client:
public class Client {
public void go() {
try {
try (
Socket socket = new Socket("localhost", 9999);
PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
) {
String input;
while ((input = bufferedReader.readLine()) != null) {
System.out.println("1");
System.out.println(input);
printWriter.println(new Scanner(System.in).nextLine());
}
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
Client client = new Client();
client.go();
}
}
Are there some problems with my code?
Your client connects and then blocks reading a line from the server.
Your server accepts the connection and then blocks reading a line from the client.
I don't know what you were expecting to happen next, but it won't. Somebody needs to send something.
Your code seems to be fine. You just need to push the infrastructure by calling flush() after writing:
printWriter.flush();
I have a client class and a server class.
If client sends message to server, server will send response back to the client, then client will print all the messages it received.
For example,
If Client sends "A" to Server, then Server will send response to client
"1111". So I use readLine() in client class to read the message from server, then client print "1111" in the console.
If Client sends "B" to Server, then Server will send response to client
"2222\n 3333". So the expected printing output from client is:
"2222"
"3333"
So the response message from server to client may have 1 line or 2 lines depending on the message it send from client to server.
My question is that how I can use readLine() to read the message that send from server to client. More specifically, if I use the following codes,
String messageFromServer;
while(( messageFromServer = inputStreamFromServer.readLine()) != null) {
println(messageFromServer);
}
It will only print the first line, and will not print anything else even if I keep sending message from client to server, because readLine() will stops once it has read the first line.
update:
More specifically, I am looking for some methods in the client class to read message that contains 1 or multiple lines from server at a time. I am wondering if there are any ways to do it in client side if I don't want to change the format of the message that sent from server to client.
update 2
To make my question more clear, I will put some sample codes in the following:
This is server:
import java.net.*;
import java.io.*;
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(1234);
} catch (IOException e) {
System.err.println("Could not listen on port: 1234.");
System.exit(1);
}
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
} catch (IOException e) {
System.err.println("Accept failed.");
}
System.out.println("Connected");
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String textFromClient =null;
String textToClient =null;
textFromClient = in.readLine(); // read the text from client
if( textFromClient.equals("A")){
textToClient = "1111";
}else if ( textFromClient.equals("B")){
textToClient = "2222\r\n3333";
}
out.print(textToClient + "\r\n"); // send the response to client
out.flush();
out.close();
in.close();
clientSocket.close();
serverSocket.close();
}
}
The client:
public class Client {
public static void main(String[] args) throws IOException {
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
try {
socket = new Socket("localhost", 1234);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host");
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection");
}
System.out.println("Connected");
String textToServer;
while((textToServer = read.readLine())!=null){
out.print(textToServer + "\r\n" ); // send to server
out.flush();
String messageFromServer =null;
while(( messageFromServer = textToServer=in.readLine()) != null){
System.out.println(messageFromServer);
}
}
out.close();
in.close();
read.close();
socket.close();
}
private static void debug(String msg)
{
System.out.println("Client: " + msg);
}
}
You shouldn't need to change the format of the data sent by the server, and readLine() should work, but I suspect that the server is not flushing or closing the OutputStream after writing the response which could possibly explain things.
Is the call to readLine() hanging? Are you in control of the server code? If so, can you include it?
Revised classes that work as I believe you expect:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class ClientServerTest2
{
public static void main(String[] args) throws Exception
{
Thread serverThread = new Thread(new Server());
serverThread.start();
Thread clientThread = new Thread(new Client());
clientThread.start();
serverThread.join();
clientThread.join();
}
private static class Server implements Runnable
{
#Override
public void run()
{
ServerSocket serverSocket = null;
try
{
serverSocket = new ServerSocket(1234);
Socket clientSocket = null;
clientSocket = serverSocket.accept();
debug("Connected");
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String textFromClient = null;
String textToClient = null;
textFromClient = in.readLine(); // read the text from client
debug("Read '" + textFromClient + "'");
if ("A".equals(textFromClient))
{
textToClient = "1111";
}
else if ("B".equals(textFromClient))
{
textToClient = "2222\r\n3333";
}
debug("Writing '" + textToClient + "'");
out.print(textToClient + "\r\n"); // send the response to client
out.flush();
out.close();
in.close();
clientSocket.close();
serverSocket.close();
}
catch (Exception e)
{
e.printStackTrace();
}
}
private static void debug(String msg)
{
System.out.println("Server: " + msg);
}
}
private static class Client implements Runnable
{
#Override
public void run()
{
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
try
{
socket = new Socket("localhost", 1234);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
debug("Connected");
String textToServer;
textToServer = read.readLine();
debug("Sending '" + textToServer + "'");
out.print(textToServer + "\r\n"); // send to server
out.flush();
String serverResponse = null;
while ((serverResponse = in.readLine()) != null)
debug(serverResponse); // read from server and print it.
out.close();
in.close();
read.close();
socket.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
private static void debug(String msg)
{
System.out.println("Client: " + msg);
}
}
Change while(( messageFromServer = inputStreamFromServer.readLine() != null) to while(( messageFromServer = inputStreamFromServer.readLine()) != null)
Actually this shouldn't even compile....
It's a work around.
If you want to send multiple strings like in your case : "2222\n 3333".
You can send them by adding a seperator character (like :) between two strings : "2222: 3333".
Then you can call write from server side as
clientOut.write("2222: 3333\n");
On client side parse recieved String :
messageFromServer = inputStreamFromServer.readLine();
String strArray[] = messageFromServer.split(":");
strArray[0] : 2222
strArray[0] : 3333
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.