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send message to specific clients using java

How can i send message from server to any specific client. I have the concept of how to do it like i have to make a list of all the clients connected to server and then by iterating each client i can send message but i will be thankful if any one can help me by code.I have searched many codes but i didn't get any considerable help from them Code shouldn't be GUI based. Thanks in advance.Sorry for my bad English.
This is my code in which message is send to all clients but i want to send message to a client of my choice using clients ipaddress
Map<Integer, java.net.Socket> clients = new HashMap<Integer, java.net.Socket> ();
socket = serverSocket.accept();
// Add the socket to a HashMap
clients.put(socket.getPort(), socket);
for (Iterator<Integer> iter = clients.keySet().iterator(); iter.hasNext(); )
{
int key = iter.next();
java.net.Socket client = clients.get(key);
// Sending the response back to the client.
// Note: Ideally you want all these in a try/catch/finally block
OutputStream os = client.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write("Some message");
bw.flush();
}

What I would do is create a Client class:
class Client
{
private String userName;
private String ipAddress;
private java.net.Socket socket = null;
public Client (String userName, String ipAddress, java.net.Socket socket)
{
this.userName = userName;
this.ipAddress = ipAddress;
this.socket = socket;
}
public java.net.Socket getSocket()
{
return this.socket;
}
}
Instead of adding just the socket and port number to the map, I would map the combination of the userName and ipAddres to a Client object.
socket = serverSocket.accept();
// get the username from the socket
// get the ipAddress from the socket
Client c = new Client(userName, ipAddress, socket);
// Add the client to a HashMap
clients.put(userName + ":" + ipAddress, c);
Now, you can send a message to a specific client based on the username and ipAddress:
public void sendToOneClient (String userName, String ipAddress, Map<String, Client> clients)
{
Client c = clients.get(userName + ":" + ipAddress);
java.net.Socket socket = c.getSocket();
// Sending the response back to the client.
// Note: Ideally you want all these in a try/catch/finally block
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write("Some message");
bw.flush();
}

I'd use Socket.getInetAddress() and compare the result to whatever you have the IPs you want to send to in. Personally, I'd use a String[] or ArrayList<String> for that. Here's an example:
ArrayList<String> addresses;
//TODO: Add things to 'addresses'
clients.put(socket.getPort(), socket);
for (Iterator<Integer> iter = clients.keySet().iterator(); iter.hasNext(); )
{
int key = iter.next();
java.net.Socket client = clients.get(key);
//Checking to make sure it's a client we want to send to.
if (addresses.contains(client.getInetAddress().toString()) {
// Sending the response back to the client.
// Note: Ideally you want all these in a try/catch/finally block
OutputStream os = client.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write("Some message");
bw.flush();
}
}
Alternatively, you could store the sockets in your HashMap by the InetAddress instead.

You can store a relationship between how you want to look up the client with the socket that they are on. The natural way to do this is with a map, like
Map<String, Socket> sockets = new HashMap<String,Socket>();
...
ServerSocket ss = ...;
Socket s = ss.accept();
String username = getUserName(s);
sockets.put(username, s);
Obviously, in this example here, the client would have to send his/her userName in a format which you expect to receive after making the Socket connection

I have found that it is effective to create an object type that can hold both a unique name or id be it an int or a String and also a Socket. You could store instances of this object in an ArrayList (or any other list) and iterate through them searching for the name or id that you want to use.

This is what I did for my program.Here I used the ">>" string to specify that a message should be sent to a particular user. (e.g.: "Ross>>Hi Ross What's Up?" means that the message should be sent to the user named 'Ross'). I used a HashMap(named 'WritersMap') to keep details as KEY-VALUE pairs. Key will be the name of the user who sends the particular message and Value will be that message. 'in' is a BufferedReader instance.
while (true) {
String input = in.readLine();
if (input == null) //if there is no input,do nothing
{
return;
}
//when a user sends a message to a specific user
else if(input.contains(">>")) //checks whether the message contains a >>
{
String person=input.substring(0,input.indexOf(">")); //extract the name of the destination user
for(HashMap.Entry<String,PrintWriter> entry:writersMap.entrySet()) //find the destination user from the users list
{
if(entry.getKey().matches(person)) //if the destination user is found
{
PrintWriter writer=entry.getValue();
writer.println("MESSAGE " + name + ": " + input);
}
}
}
else //when a user sends a broadcast message to all users
{
for(HashMap.Entry<String,PrintWriter> entry:writersMap.entrySet()) //find the destination user from the users list
{
PrintWriter writer=entry.getValue();
writer.println("MESSAGE " + name + ": " + input);
}
}
}

Java Message sent from client to server

I'm using a socket to connect my client with the server, I need a way so that when somebody tries to login on the client with an account, it sends the username and password to the server, and checks if the account exists. I just need to know how to make it send the message to the server when they press login.
i tried this to make it send a message to the server
public static void sendmsg(String a, String b)
{
try
{
String host = "127.0.0.1";
int port = 43655;
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);
//Send the message to the server
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
String sendMessage = a;
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();
}
}
}

nice you are working with Sockets, well I have an approach you can try, and maybe if it is useful you can consider for your implementation.
First of all I will create an entity to handle those values and fill it with the incoming data.
class UserAuth {
private String username;
private String password;
//Consider here your getters and setters, I am not including them
}
I will use the entity as the parameter for the method while sending and maybe you can fill it as something like:
UserAuth attemptingUser = new UserAuth(...)
ObjectInputStream works fine for these kind of scenarios. If you still want to work with Strings, you can use BufferedReader and try to merge your username and password as one single String and use the .readLine() method to obtain (separated with commas), then use String methods such Split but I find that could take some more time, should be better if you handle it with an object. But it depends on the complexity you want to add to your application :).
class AuthClient {
public void sendMsg(UserAuth attemptingUser) {
String host = "localhost";
int port = 2055;
//1. Create the socket
Socket sender = new Socket(host, port);
//2. Create an object output stream to write the object into the stream
ObjectOutputStream outputWriter = new ObjectOutputStream(sender.getOutputStream());
//3. Write (send the object)
outputWriter.writeObject(attemptingUser);
//4. Close
outputWriter.close();
sender.close();
}
}
class AuthServer {
ServerSocket ss = new ServerSocket(2055);
public void receiveMsg() {
//1. Accept the connection
Socket conn = ss.accept();
//2. Receive the flow
ObjectInputStream readStream = new ObjectInputStream(conn.getInputStream());
//3. Read the object
UserAuth userReceived = readStream.readObject();
//4. Verify against file, db or whatever
if (userReceived.getUsername().equals("admin") && userReceived.getPassword().equals("admin")) {
//Authentication
}
}
}
(This is added as the part I edit for what you asked me in the comments)
public void sendMsg(String username, String password) {
String host = "localhost";
int port = 2055;
//1. Create the socket
Socket sender = new Socket(host, port);
//2. Create the UserAuth object based on the parameters you received
UserAuth myuser = new UserAuth();
myuser.setUsername(username);
myuser.setPassword(password);
//3. Follow same instructions for the creation of ObjectOutputStream...
ObjectOutputStream objectWriter = new ObjectOutputStream(sender.getOutputStream());
objectWriter.writeObject(myuser);
//That is what I would use if I keep your structure
}
If you want to keep your structure using Strings, I would simplify and reduce impact of I/O by using the String methods. Since you know you are always expecting user/password, I would merge your two params in one single String or use special char and on server side handle with StringTokenizer class. Or maybe handle with the "split" method. You have many options here.
So far, this will be my approach for the problem you are facing. Hope it helps somehow. Best regards and happy coding :).

What you have done looks OK to me but it all depends on what the server is expecting to receive. What is the terminating character as you have not sent one unless it's already contained within your String a variable.
If the server is expecting an end of line character (which you don't currently send) you can use a PrintWriter instead of a BufferedWriter like this
pw = new PrintWriter(socket.getOutputStream(), true);
pw.println(a);
Your server would then be doing something like this
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String value = br.readLine();

(Client - Server) Java control when Server's serversocket accepts client(s) is not working [closed]

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Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 8 years ago.
Improve this question
I am currently learning about Sockets and my homework is to create a chat room where multiple clients can talk freely. The hint given by the teacher was that the chat room server only accepts the client when the client attempts to send a message. This homework is supposed to be done without using threads.
Following the hint given, I tried to create unbound ServerSocket and Socket in both the client and the server code. The key idea is that when the client attemps to send a message to the server, the client code would connect the unbound Socket, which will then trigger the server to connect the unbound ServerSocket and to accept the client.
However, when I run the code, both the server and client code are running, and they claim that all the connections are made, but I could not transmit messages between the client and the server at all.
I have tried finding answers online, but I could not find any. I would like to ask if my way of deciding when the server accepts the client is correct.
my ChatRoom Server:
public class ChatRoom {
public static void main(String[] args) throws Exception {
int portNum = 4321;
ServerSocket serverSocket = new ServerSocket();
int count = 1;
while (true) {
// redeclare everything each round
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
BufferedReader stdIn = null;
String inputLine = null;
// accept each time round
serverSocket.bind(new InetSocketAddress(portNum));
socket = serverSocket.accept();
System.out.println("newly accepted!");
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
stdIn = new BufferedReader(new InputStreamReader(System.in));
if (!((inputLine = in.readLine()).equals("Bye"))) {
System.out.println("Client says: " + inputLine);
out.println(stdIn.readLine());
out.flush();
System.out.println("Message Count: " + count);
count++;
}
else {
out.println(inputLine);
serverSocket.close();
socket.close();
out.close();
in.close();
}
}
}
}
my ChatRoomClient:
public class ChatRoomClient {
public static void main(String[] args) throws Exception {
String hostName = "localhost";
int portNumber = 4321;
Socket echoSocket = new Socket(); // creates an unbound socket
PrintWriter out = null;
BufferedReader in = null;
BufferedReader stdIn = null;
String userInput;
do {
out = null;
in = null;
stdIn = null;
// each time round the unbound socket attempts to connect to send a message
echoSocket.connect(new InetSocketAddress(hostName, portNumber));
System.out.println("successfully connected");
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
stdIn = new BufferedReader(new InputStreamReader(System.in));
userInput = stdIn.readLine();
out.flush();
System.out.println("Server says: " + in.readLine());
}
while (!userInput.equals("Bye"));
// close everything
echoSocket.close();
in.close();
stdIn.close();
}
}
Thanks!

The hint given by the teacher was that the chat room server only accepts the client when the client attempts to send a message. This homework is supposed to be done without using threads.
The hint given by the teacher doesn't make sense. The client has to connect, then the server accepts. The client can't send a message without connecting first. Maybe the teacher really means that the client shouldn't connect until he has something to send?
Following the hint given, I tried to create unbound ServerSocket and Socket in both the client and the server code. The key idea is that when the client attemps to send a message to the server, the client code would connect the unbound Socket, which will then trigger the server to connect the unbound ServerSocket and to accept the client.
But that won't happen. It's impossible. If you try to connect to a port that isn't listening, you will get a ConnectException. The only way to put the port into listening state is to bind the ServerSocket. There is no magical back-door by which the server can possibly know that the client wants to connect so it should now do the bind.
This homework is supposed to be done without using threads.
Impossible to 'create a chat room where multiple clients can talk freely' that way, unless you are expected to use non-blocking I/O, or abuse the available() facility, or use a connection per message, but then I don't see how you can communicate one client's messages to the other clients, unless you're allowed to batch them up.
There are too many imponderable aspects of this assignment as you have described it. The question as posed doesn't actully make sense, and your proposed solution certainly doesn't. You should just go ahead and write your program the normal way, with a connect, an accept, and some I/O. Get it working while your teacher comes up with a clarification.

Ah... With out using thread for the server you will not be able to serve multiple clients. Anyway, your current codes have issues and your logic are not correct.
Your stdIn should be declare and instantiated outside of the loop, you don't need to keep on creating the stdIn object for each loop.
Your "in" socket accept() and echoSocket.connect() should also be outside of the loop, this is why you are not getting any answer from the server because you are not listening on the same line. It's like your phone, keep on FLASH to dial the new number each time. all point to the same server, but it is different connection.
So, the idea is to establish a connection between server and client (single connection) that can communicate both way (via input and output stream). Then you can loop and talk start with the client, then server receive, then server talk, then client receive then client talk.... until client say Bye...
for more: http://ta.cnci.org/basicirc

thought I would like to update, I managed to solve my problem without using threads. Just sockets haha. Thought it would be good to post my answer for reference..
my ChatRoom Server:
public class ChatRoomServer {
public static void main(String[] args) throws Exception {
ServerSocket serverSocket = new ServerSocket(4321);
while(true) {
Socket clientSocket = serverSocket.accept();
BufferedReader in = new BufferedReader
(new InputStreamReader(clientSocket.getInputStream()));
String inputLine = in.readLine();
System.out.println("Client says: " + inputLine);
in.close();
clientSocket.close();
}
}
}
my ChatRoom Client:
public class ChatRoomClient {
public static void main(String[] args) throws Exception {
String hostName = "localhost";
int portNum = 4321;
BufferedReader stdIn = new BufferedReader
(new InputStreamReader(System.in));
while (true) {
String userInput;
userInput = stdIn.readLine();
Socket echoSocket = new Socket(hostName, portNum);
PrintWriter out = new PrintWriter
(echoSocket.getOutputStream(), true);
out.println(userInput);
out.flush();
out.close();
echoSocket.close();
if (userInput.equals("Bye")) {
stdIn.close();
break;
}
}
}
}

Client-Server Socket: Not reaching if statement [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why isn't my application entering my if statement
I'm trying to write a console client-server application in Java; using sockets, I currently have a simple login system and a simple command system. The login system appears to work, and the connection seems to be working.
However, the command system does not seem to function at all, when the command is received by the server, it does not appear to send anything back.
So my main question is why doesn't my server send anything back to the client when the command is received?
Here is my Server:
import java.io.*;
import java.net.*;
class TCPServer2
{
public static void main(String argv[]) throws Exception
{
//error is caused by command being used differently to login & username/password strings.
//consider removing command as a set string and adding a statement which takes
//the readLine value, adds it to a string and the command is the value of said string.
//If string is = "listLanguages" do this else if = "getcost" do this else "invalid cmd".
ServerSocket welcomeSocket = new ServerSocket(6789);
Map<String, String> userDetails = new HashMap<String, String>();
userDetails.put("JOHN","UNCP");
userDetails.put("MATT","UNCP");
String Command;
String username;
String username1;
String password;
String password1;
String cmd;
while(true)
{
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient =
new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
username = inFromClient.readLine();
System.out.println("\nUsername received: " + username);
password = inFromClient.readLine();
System.out.println("\nPassword received: " + password);
username1=username.toUpperCase();
password1=password.toUpperCase();
if (userDetails.get(username1).equals(password1))
{
outToClient.writeBytes("Hello " + username1);
outToClient.writeBytes("\nOther users registered on the server currently include: \n");
for (String str : userDetails.keySet())
{
outToClient.writeBytes(str);
}
}
else
{
outToClient.writeBytes("Invalid Username and/or password.\n");
}
BufferedReader inFromClient2 =
new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient2 = new DataOutputStream(connectionSocket.getOutputStream());
Command = inFromClient2.readLine();
System.out.println("\nCommand received: " + Command);
if(Command.equals("listTranslations"))
{
outToClient2.writeBytes("English,Thai,Geordie,etc.");
}
else
{
if(Command.equals("getCost"))
{
outToClient2.writeBytes("£100\n");
}
else
{
outToClient2.writeBytes("Invalid Command");
}
}
}
}
}
Here is my client:
import java.io.*;
import java.net.*;
class TCPClient2
{
public static void main(String argv[]) throws Exception
{
String userName;
String passWord;
String loginInfo;
String loginInfo2;
String loginInfo3;
String command;
String commandInfo;
String commandInfo2;
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()));
System.out.println("Username: ");
userName = inFromUser.readLine();
outToServer.writeBytes(userName + "\n");
System.out.println("Password: ");
passWord = inFromUser.readLine();
outToServer.writeBytes(passWord + "\n");
loginInfo = inFromServer.readLine();
System.out.println(loginInfo);
loginInfo2 = inFromServer.readLine();
System.out.println(loginInfo2);
loginInfo3 = inFromServer.readLine();
System.out.println(loginInfo3);
System.out.println("Please enter a command: ");
command = inFromUser.readLine();
outToServer.writeBytes(command);
commandInfo = inFromServer.readLine();
System.out.println(commandInfo);
commandInfo2 = inFromServer.readLine();
System.out.println(commandInfo);
clientSocket.close();
}
}
Here's how it's supposed to work:
The client connects to the server,
The client asks user to login,
The user inputs his login info,
The server checks the login info,
The server tells the client it's logged in successfully,
The client asks the user to input a command,
The user inputs a command (to request a price),
The command is sent to the server,
The server sends back the desired in info,
It should then loop back to the user being asked to input a command.
However, it does not do this. It gets stuck after the user logs in, on the "Other users registered on the server currently include:" line, without printing any data.
Why is it doing this?

Why it's getting stuck is probably because both client and server are on a readLine() resulting in a deadlock. Client waits for incomming data and so is the server, Since this is a command promt client and server, and you have no "button" to send the data with.
I would add info showing which variable it is printing at the moment so you can easily follow where it gets stuck. Example:
loginInfo = inFromServer.readLine();
System.out.println("loginInfo client Side "+loginInfo);
This will show you that it's printing the loginInfo variable located in the client. Now you can easily follow the flows and locate where it's going wrong.
I've never done a command promt server/client (only gui), but when you are printing your list of users with your current design, you might want to to build a string with all usernames, send the whole string over to the client, and then the client separates the string with StringBuilder and prints the result. This is because the client will not know how many "usernames" the server will send

Have you tried flushing the buffer of the data output stream writer before you send the next line. I'm also curious why you use two different data output stream writers and input stream readers for one client. Couldn't you just use the same ones for both parts of your program.

The issue is with improper socket data read/write methods. You have to always flush() when you are writing data to sockets. If you comment line
//loginInfo3 = inFromServer.readLine();
//System.out.println(loginInfo3);
Then you can see that the client displays the "Please enter a command" but after you enter the command the socket is not flushed/closed so the server keeps waiting.
The main issue with the Server and Client code is proper hand shake. You have to write code in a block, open socket, write command, get response and close socket. This should be a common way of entering the data. You have clubbed sockets and writing data to the streams without proper flush/close, hence it is waiting at different points.

server client communication java

I have this client, the server information is not important. The output of this code is very random.
class Client {
public static void main(String args[]) throws Exception
{
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("127.0.0.1", 10004);//this will become the addr of the server you want to input.
InetAddress host = clientSocket.getInetAddress();
// System.out.println(host);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
boolean exit = false;
while (!exit) {
while (inFromServer.ready()) {
System.out.println(inFromServer.readLine());
}
String sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + "\n");
}
clientSocket.close();
}
}
If I run this in debug mode, it has always the correct result. E.g.
please insert password
the user types pass
pass correct
please type command
and you type command
etc
etc
When it's not in debug mode, all goes wrong. I don't even get the initial request from server. What is going on? I think the read line might be executed too fast?

in.ready() does not wait for any data to be available. It the server hasn't sent the data yet when you client reads that line, you're going to skip the readLine() completely.
Just remove that while and do a plain readLine().
If there are phases where you need to wait for multiple lines from the server, you'll need to implement more logic. Usually, the server will send an "end of message" marker to signify to the client that it is done. For example, when the server is done, it could send the message "END-OF-MESSAGE". In the client code, you would do:
boolean serverDone = false;
while (!serverDone) {
String message = in.readLine();
if (message == null) {
// handle this problem: the server has closed the connection
serverDone = true; // or return, or throw
} else if ("END-OF-MESSAGE".equals(message)) {
serverDone = true;
}
}