I am building a small chat application in which client A wants to send something to client C with server B in between. First of all is this a correct approach for the problem??. I am able to send and receive data to and from a server but it is limited to only the client.For example if Client A sends data to server B and client C is sending data to server B then i can send data back to A and C just like an echo server. But what i want is to forward data coming from Client A to Client C via server B.
The following is the server code:
public class Server {
public static void main(String[] args) {
int port = 666; //random port number
try {
ServerSocket ss = new ServerSocket(port);
System.out.println("Waiting for a client....");
System.out.println("Got a client :) ... Finally, someone saw me through all the cover!");
System.out.println();
while(true) {
Socket socket = ss.accept();
SSocket sSocket = new SSocket(socket);
Thread t = new Thread(sSocket);
t.start();
System.out.println("Socket Stack Size-----"+socketMap.size());
}
}
catch (Exception e) { }
}
}
class SSocket implements Runnable {
private Socket socket;
public SSocket(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
try {
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
DataInputStream dIn = new DataInputStream(in);
DataOutputStream dOut = new DataOutputStream(out);
String line = null;
while (true) {
line = dIn.readUTF();
System.out.println("Recievd the line----" + line);
dOut.writeUTF(line + " Comming back from the server");
dOut.flush();
System.out.println("waiting for the next line....");
}
}
catch (Exception e) { }
}
}
The client code is :
public class Client {
public static void main(String[] args) {
int serverPort = 666;
try {
InetAddress inetAdd = InetAddress.getByName("127.0.0.1");
Socket socket = new Socket(inetAdd, serverPort);
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
DataInputStream dIn = new DataInputStream(in);
DataOutputStream dOut = new DataOutputStream(out);
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Type in something and press enter. Will send it to the server and tell ya what it thinks.");
System.out.println();
String line = null;
while (true) {
line = keyboard.readLine();
System.out.println("Wrinting Something on the server");
dOut.writeUTF(line);
dOut.flush();
line = dIn.readUTF();
System.out.println("Line Sent back by the server---" + line);
}
}
catch (Exception e) { }
}
}
When your clients connect to the server, your server creates a Socket for it, here it is Socket socket = ss.accept();, your socket variable will be holding that client.
now if you just keep adding your client socket to a arraylist in your while loop, you will have a list of clients actively connected with your server like:
after the accept:
clients = new ArrayList<DataOutputStream>();
Socket socket = ss.accept();
os = new DataOutputStream(socket.getOutputStream());
clients.add(os);
Now as you have all the clients in that clients arraylist, you can loop through it, or with some protocol define which client should i send the data after reading.
Iterator<DataOutputStream> it = clients.iterator();
while ((message = reader.readLine()) != null) { //reading
while (it.hasNext()) {
try {
DataOutputStream oss = it.next();
oss.write(message);//writing
oss.flush();
}
catch (Exception e) { }
}
}
This will loop through all the available clients in the arraylist and will send to all. you can define ways to send to only some.
For example:
maintain a ActiveClients arraylist and with some GUI interaction may be or maybe, define what all clients you want to send the message.
Then add just those clients outputStreams to ActiveClients
ActiveClients.add(clients.get(2));
or remove them, if you don't want them.
ActiveClients.remove(clients.get(2));
and now just loop through this arraylist to send the data as above.
You can create message queue for each client:
Client A sends message 'Hi' with address Client C to server B.
Server B receives message and adds it to message queue of client C.
Thread in server B which communicates with client C check message queue, retrieve message and sends it to client C.
Client C receives message.
If I am not mistaken, you must be having a problem with receiving a message from the Server or SSocket class. What happens with your code is that when you send a message from the client to the server the Server class receives your messages also gives an echo of the message in the client. However, when you send a message from the Server class, you don't get any messages in the Client Class.
To get this to work, you would have to modify your code in the following fashion:
SSocket Class
String line = null;
while (true) {
line = dIn.readUTF();
System.out.println("Recievd the line----" + line);
dOut.writeUTF(line + " Comming back from the server");
dOut.flush();
System.out.println("waiting for the next line....");
}
You should add these lines:
String Line2 = take.nextLine(); //The user types a message for the client
dOut.writeUTF(Line2 + " Comming back from the server"); //The message is sent to the client
Replace the while loop with this one and it will work fine.
while (true) {
line = dIn.readUTF(); //Takes the msg from the client
System.out.println("Recievd the line----" + line); //Prints the taken message
String Line2 = take.nextLine(); //The user types a message for the client
dOut.writeUTF(Line2 + " Comming back from the server"); //The message is sent to the client
dOut.flush();
System.out.println("waiting for the next line....");
}
Related
So, I just learned how to make sockets and all that good stuff in Java, and so my first try got me a message from the client, and then the client crashing. What was supposed to happen was get a message from the client, if that message is equal to this, then send data back. However, the if function for if the message was correct wasn't firing, even though the message was correct.
Even when I remove the if function to check if the string was right or not, the program still freezes up. And by the way, my server is a console application, and my client is a SWT application.
Here's the server code with the removed if function:
try {
System.out.println("Waiting for a connection...");
// Start a server
ServerSocket server = new ServerSocket(3211);
// Listen for anyone at that port
Socket socket = server.accept();
System.out.println("The client has connected!");
// Get the data being sent in
DataInputStream inputStream = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
DataOutputStream ouputStream = new DataOutputStream(socket.getOutputStream());
// Turn that into UTF-8
String data = inputStream.readUTF();
System.out.println("Received " + data);
ouputStream.writeUTF("Great!");
System.out.println("Awesome!");
socket.close();
inputStream.close();
ouputStream.close;
server.close();
System.out.println("Socket closed\n-----------------------------");
}
catch(IOException e) {
System.out.println(e);
}
And the client (which is fired when a button gets pressed):
try {
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\nConnecting to the server...");
Socket socket = new Socket("192.168.1.206", 3211);
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\nConnected to the server!");
DataInputStream input = new DataInputStream(System.in);
DataOutputStream output = new DataOutputStream(socket.getOutputStream());
output.writeUTF("sweet");
String data = input.readUTF();
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\nSERVER: " + data);
input.close();
output.close();
socket.close();
}
catch (IOException er) {
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\n" + er);
}
As soon as I press the button to try and start the connection (with the server already running), the client instantly freezes. It doesn't even send any of the "connecting to server" kind of stuff.
Any idea what's going wrong, and how to fix this?
Your client is reading from System.in. It should be reading from the socket input stream.
NB You only need to close the outermost output stream of a socket. That flushes it if necessary and closes the input stream and the socket. You're presently not only closing more than necessary but also in the wrong order,
Your socket is unable to send data because you did not called .flush() method on your outputstream reference. Use this one and you don't have to write flush() and close() method explicitely on streams
Server Code
System.out.println("Waiting for a connection...");
// Start a server
try (ServerSocket server = new ServerSocket(3211)) {
// Listen for anyone at that port
try (Socket socket = server.accept()) {
System.out.println("The client has connected!");
// Get the data being sent in
try (DataInputStream inputStream = new DataInputStream(new BufferedInputStream(socket.getInputStream()))) {
try (DataOutputStream ouputStream = new DataOutputStream(socket.getOutputStream())) {
// Turn that into UTF-8
String data = inputStream.readUTF();
System.out.println("Received " + data);
ouputStream.writeUTF("Great!");
System.out.println("Awesome!");
}
}
}
System.out.println("Socket closed\n-----------------------------");
} catch (IOException e) {
System.out.println(e);
}
Client Code
try {
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\nConnecting to the server...");
try (Socket socket = new Socket("127.0.0.1", 3211)) {
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\nConnected to the server!");
try (DataInputStream input = new DataInputStream(socket.getInputStream())) {
try (DataOutputStream output = new DataOutputStream(socket.getOutputStream())) {
output.writeUTF("sweet");
}
String data = input.readUTF();
System.out.println(String.format("data received from server '%s':\n", data));
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\nSERVER: " + data);
}
}
} catch (IOException er) {
allMessagesTextBox.setText(allMessagesTextBox.getText() + "\n" + er);
}
Output on Server
Waiting for a connection...
The client has connected!
Received sweet
Awesome!
Socket closed
-----------------------------
Output on Client
data received from server 'Great!':
Now moving to problem in your code.
See the client side code you have written DataInputStream input = new DataInputStream(System.in); instead of DataInputStream input = new DataInputStream(socket.getInputStream())
which causes the failure in receiving message from server
I've been working on a simple Android TCP Server, so I can connect from a TCP Client and pass data back and forth.
I am encountering an weird problem, my android phone creates the TCP Socket, and I am able to connect to it via Hercules utility (A TCP client). The connection goes through, however the program is still blocking at the ServerSocket.accept() method.
Could anyone shed some light on this issue? Here is my java function.
public void TcpServer()
{
try
{
Socket s = null;
ServerSocket ss = null;
System.out.println("TCP Server Starting");
ss = new ServerSocket(27015);
s = ss.accept();
System.out.println("New connection! Yay");
BufferedReader input = new BufferedReader(new InputStreamReader(s.getInputStream()));
String incomingMsg = input.readLine();
System.out.println("Received: " + incomingMsg);
}
catch (Exception e)
{
}
}
I wrote code can send a message to server. Problem is if I capture communication in Wireshark my string message sent from my application looks like this:
hello - 1 packet
If I check the same message sent from Telnet cmd terminal message looks like this:
h - 1 packet
e - 1 packet
l - 1 packet
l - 1 packet
o - 1 packet
So finally it sent entire string by character. Server can read the message from cmd Telnet terminal and reply but can't read the message sent from my application. Is there some way how can I send string like this? I'm not programming server. I'm programming only client side so it's important server has to able read the message correctly. Thanks a lot!
PrintWriter out;
BufferedReader in;
public void run() {
// TODO Auto-generated method stub
try {
InetAddress serverAddr = InetAddress.getByName(hostname);
// create a socket to make the connection with the server
socket = new Socket(serverAddr, port);
Log.i("Terminal", "Socket connecting");
try {
// send the message to the server
out = new PrintWriter(
new BufferedWriter(new OutputStreamWriter(
socket.getOutputStream())), true);
Log.i("Terminal", "Connected.");
// receive the message which the server sends back
in = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
}catch...
}catch...
}
//send code
public void sendMessage(String message) {
if (out != null && !out.checkError()) {
out.println(message);
out.flush();
Log.i("Terminal", "Message sent.");
}
}
Why not just send each character separately?
Something like this:
public void sendMessage(String message) {
for (String ch : message.split(""))
sendPacket(ch);
sendPacket("\r\n");
}
public void sendPacket(String payload) {
if (out != null && !out.checkError()) {
out.print(payload);
out.flush();
Log.i("Terminal", "Message sent.");
}
}
You said everything was working fine, but if you do run in to issues with packet coalescing in the future you can disable the Nagle algorithm by adding this line:
socket.setTcpNoDelay(true);
right after this one:
socket = new Socket(serverAddr, port);
I would like to take text from a file and then send it to the server for it to capitalise before sending back to the client where it is printed out. How do I achieve this?
I can read one line and send that back to the client and I've managed to write multiple lines to the output stream (for the server to read) but I don't know what to do now..
I have a client that reads text from a file:
import java.io.*;
import java.net.*;
import java.util.Date;
public class Client
{
public static void main(String[] args)
{
try
{
// First create the input from keyboard
BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Client Program");
// Next we need to find out the IP address and port number of the server
System.out.print("Enter IP Address of server: ");
String ip = input.readLine();
System.out.print("Enter port number of server: ");
String port_string = input.readLine();
// The port number needs to be an int, so convert the string to an int
int port = Integer.parseInt(port_string);
// Connect to the server
Socket sock = new Socket(ip, port);
// Create the incoming stream to read messages from
DataInputStream network = new DataInputStream(sock.getInputStream());
//Create the output stream to the client
DataOutputStream message = new DataOutputStream(sock.getOutputStream());
//Send message
//message.writeUTF("some text");
FileReader file = new FileReader("text.dat");
BufferedReader input_file = new BufferedReader(file);
// Loop until EOF
while (input_file.ready()){
// Read next line from the file
String line = input_file.readLine();
// Write line to server
message.writeUTF(line + "\n");
//System.out.println(line);
}
// Display our address
System.out.println("Address: " + sock.getInetAddress());
String line;
// Loop until the connection closes, reading from the network
while ((line = network.readUTF()) != null)
{
// Display the received message
System.out.println(line);
}
}
catch (IOException ioe)
{
// This is expected when the server closes the network connection
System.err.println("Error in I/O");
System.err.println(ioe.getMessage());
System.exit(-1);
}
}
}
And then a server that is supposed to take those strings and capitalise them:
import java.io.*;
import java.net.*;
import java.util.*;
public class Server
{
public static void main(String[] args)
{
try
{
// First create the input from the keyboard
BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Server Program");
// Get the port to listen on
System.out.print("Enter port number to listen on: ");
String port_string = input.readLine();
// The port number needs to be an int, so convert the String to an int
int port = Integer.parseInt(port_string);
// Create a ServerSocket to listen on this address
ServerSocket server = new ServerSocket(port);
// Accept an incoming client connection on the server socket
Socket sock = server.accept();
// Create the output stream to the client
DataOutputStream network = new DataOutputStream(sock.getOutputStream());
//Create the incoming stream to read messages from
DataInputStream message = new DataInputStream(sock.getInputStream());
String newLine = inFromClient.readLine();
//Line to read
String line;
line = message.readUTF();
line = line.toUpperCase();
// Send message
network.writeUTF(newLine);
// Close sockets. This will cause the client to exit
sock.close();
server.close();
}
catch (IOException ioe)
{
System.err.println("Error in I/O");
System.err.println(ioe.getMessage());
System.exit(-1);
}
}
}
The problem is your server is reading the stream only once and closing the socket connection.
How will your server know you have finished sending the client data to the server socket ?
You should modify the server to listen to the port till you have finished sending the whole text. For that do something like -
String newLine;
while ( true )
newLine = inFromClient.readLine();
if (newLine.equalsIgnoreCase("END"))
{
break;
}
newLine = newLine.toUpperCase();
// Send message
network.writeUTF(newLine);
}
// Close sockets. This will cause the client to exit
sock.close();
server.close();
And from the client send "END" after all lines have been sent.
The easiest way is to use IOUtils from Apache Commons. IOUtils.readLines will return a list of Strings
Exact same question : Read/convert an InputStream to a String
i've a minimal server which wait until a client connect ,then he start a thread which will send a reply back to the client, the problem is the reply.
This is the code of the server:
int port = 1234;
ServerSocket servSock = null;
servSock = new ServerSocket(port);
while (true) {
Socket link = servSock.accept();
serverThread st = new serverThread(link);
st.start();
}
This is the code of the run() method of the thread,the one which send the answer back, sk is the socket "link" passed by parameter in the server code
public void run() {
String dato = "";
InputStream i = null;
try {
i = sk.getInputStream();
} catch (IOException ex) {
Logger.getLogger(serverThread.class.getName()).log(Level.SEVERE, null, ex);
}
Scanner input = new Scanner(i);
//i receive the data sent
while (input.hasNext()) {
dato += input.nextLine();
}
// then i send a reply
DataOutputStream outputStream=new DataOutputStream(sk.getOutputStream());
outputStream.writeInt(1);
outputStream.close();
Client side ( only the code which should receive the answer from the server) :
Socket link;
int valid = 0;
String url="localhost";
int port=1234;
link = new Socket(InetAddress.getByName(url), port);
//i've to send some data to the server
PrintWriter output = new PrintWriter(link.getOutputStream(), true);
String a = new String(Base64.encode(mex));
output.println(createXml(tag, a));
output.flush();
//then i need to receive an answer from the server
DataInputStream answerI = new DataInputStream(link.getInputStream());
while(answerI.available()!=0)// but answerI.available() is always equal 0
valid = answerI.readInt();
answerI.close();
output.close ();
link.close();
With this code the istruction valid = answerI.readInt(); is not reached.
Without the while cycle, the client freeze at line : valid = answerI.readInt();
Can anyone help me?
Thank you in advance
I'm guessing that the server is blocked in a call to input.hasNext(). This will return false when the socket is closed, and its InputStream returns -1 to signal the end of the stream. However, the socket is still open. The client can send another line; the Scanner is blocking to see what the client's next move will be.
There are ways to shutdown "half" of a socket, so that the server can tell that the client has closed its sending channel but can still receive a response.
However, this approach is complicated. I suggest a change to the protocol so that the server can determine when it is allowed to respond.
In this protocol you don't need the reply if it is always '1'. Just close the socket. The client should block in a read() which will return -1 when the server closes the socket.