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How to send messages between two UDP clients?

What i'm trying to do is group 2 clients and make them communicate with eachother. So if 2 clients are connected they would only be able to communicate with eachother and if a third client got connected it would not be able to communicate with the 2 other clients but it would create another group of 2 clients and so on... Right now if a client sends a message it send it over to all clients but i'm not sure how to make them communicate in groups of 2 like in a peer-to-peer connection.
class Server {
private static DatagramSocket socket = null;
private static Map<Session, Integer> sessions = new HashMap<Session, Integer>();
private static Session session = new Session();
public static void main(String[] args) {
try {
socket = new DatagramSocket(6066);
} catch (SocketException e) {
System.out.println("[SERVER] Unable to launch server on port: " + socket.getLocalPort());
}
System.out.println("[SERVER] Server launched successfully on port " + socket.getLocalPort());
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
byte[] buffer = new byte[100];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
while (true) {
Arrays.fill(buffer, (byte) 0);
try {
socket.receive(packet);
} catch (IOException e) {
System.out.println("[SERVER] Unable to receive packets from buffer");
}
InetAddress ip = packet.getAddress();
int port = packet.getPort();
String data = new String(packet.getData()).trim();
if(session.getIp1() == null) {
session.setIp1(ip);
session.setPort1(port);
session.setData1(data);
} else {
session.setIp2(ip);
session.setPort2(port);
session.setData2(data);
}
DatagramPacket pt = new DatagramPacket(packet.getData(), packet.getData().length, ip, port);
try {
socket.send(pt);
} catch (IOException e) {
System.out.println("[SERVER] Unable to send packets to client.");
}
}
}
});
thread.start();
}
}
Client:
public class Client {
private static DatagramSocket socket = null;
public static void main(String[] args) {
System.out.println("Send to server:");
Scanner scanner = new Scanner(System.in);
while (true) {
try {
// port shoudn't be the same as in TCP but the port in the datagram packet must
// be the same!
socket = new DatagramSocket();
} catch (SocketException e1) {
System.out.println("[CLIENT] Unable to initiate DatagramSocket");
}
InetAddress ip = null;
try {
ip = InetAddress.getByName("127.0.0.1");
} catch (UnknownHostException e) {
System.out.println("[CLIENT] Unable to determine server IP");
}
// must be in a while loop so we can continuously send messages to server
String message = null;
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
receive();
}
});
thread.start();
while (scanner.hasNextLine()) {
message = scanner.nextLine();
byte[] buffer = message.getBytes();
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, ip, 6066);
try {
socket.send(packet);
} catch (IOException e) {
System.out.println("[CLIENT] Unable to send packet to server");
}
}
}
}
private static void receive() {
// receiving from server
byte[] buffer2 = new byte[100];
DatagramPacket ps = new DatagramPacket(buffer2, buffer2.length);
while (true) {
try {
socket.receive(ps);
} catch (IOException e) {
System.out.println("[CLIENT] Unable to receive packets from server.");
}
System.out.println("[SERVER] " + new String(ps.getData()));
}
}
}
Object class:
public class Session {
private InetAddress ip1;
private int port1;
private String data1;
private InetAddress ip2;
private int port2;
private String data2;
public Session() {
}
public InetAddress getIp1() {
return ip1;
}
public void setIp1(InetAddress ip1) {
this.ip1 = ip1;
}
public int getPort1() {
return port1;
}
public void setPort1(int port1) {
this.port1 = port1;
}
public String getData1() {
return data1;
}
public void setData1(String data1) {
this.data1 = data1;
}
public InetAddress getIp2() {
return ip2;
}
public void setIp2(InetAddress ip2) {
this.ip2 = ip2;
}
public int getPort2() {
return port2;
}
public void setPort2(int port2) {
this.port2 = port2;
}
public String getData2() {
return data2;
}
public void setData2(String data2) {
this.data2 = data2;
}
}

Currently, you store the client's information in an array. Make an object where it will contain two client session's data. When a new client is attempting to connect, see if there are any objects that have a free spot, if not, create a new object and await a new participant; otherwise, join an existing session.
Hackish way: Create a Map<ObjectHere, UserCount> then filter based on userCounts = 1 and then join the session to the first returned Object.

Java DatagramSocket doesn't receive data

I'm writing a simple client / server in java and I got this problem that I cannot fix.
I'm using DatagramSocket on both client and server and my server just cannot receive any data. I don't get any errors but it just doesn't work.
Here is my source code for server:
public class GameServer {
public static final String serverBuild = "0.00 (050319.milestone0-main)";
public static final String protocolBuild = "1";
public DatagramSocket serverSocket;
public boolean isRunning = false;
public Thread clientHandler;
public GameServer(int port, String serverName) {
System.out.println("Server> Starting a server on port: " + port + ".");
System.out.println("Server> " + serverName + " running on server build " + serverBuild + ".");
System.out.println("Server> Using protocol ID: " + protocolBuild + ".");
isRunning = true;
try {
serverSocket = new DatagramSocket(port);
}catch(Exception ex) {
System.out.print("Server> ");
ex.printStackTrace();
}
clientHandler();
}
public void clientHandler() {
clientHandler = new Thread(new Runnable() {
public void run() {
while(isRunning) {
byte[] buffer = new byte[256];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
try {
serverSocket.receive(packet);
System.out.println("Server> " + new String(packet.getData(), 0, packet.getData().length));
} catch (IOException e) {
System.out.print("Server> ");
e.printStackTrace();
}
}
}
});
clientHandler.start();
}
}
Here is my source code for client:
public class GameClient {
public GameClient() {
try {
DatagramSocket socket = new DatagramSocket(25567);
byte[] buffer = new byte[256];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, InetAddress.getByName("192.168.0.24"), 25567);
socket.send(packet);
}catch(Exception ex) {
ex.printStackTrace();
}
}
}
Client is very simple because I was looking why my server doesn't work.

The console does not print anything, because the client sends the package is an empty array. The server is work right.

Java Socketing: My server class constantly takes in input but my client doesn't?

Try to do some concurrent messaging between the server and the client. When they first connect to eachother and the Server sends the test string, the client gets it perfectly fine the first time. And the client can SEND messages just fine to the Server. But my Client class cant constantly check for messages like my Server can and idk what's wrong. Any suggestions?
Server class code:
import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.Random;
import java.util.concurrent.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Server {
String testMessage = "You are now connected and can begin chatting!";
boolean connected = false;
int port;
public Server(int port) {
this.port = port;
}
public void Open() {
//creates Threadpool for multiple instances of chatting
final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
Runnable serverTask = new Runnable() {
#Override
public void run() {
try {
System.out.println("Opening...");
ServerSocket srvr = new ServerSocket(port);
while (true) {
Socket skt = srvr.accept();
clientProcessingPool.submit(new ClientTask(skt));
}
} catch (Exception e) {
try {
System.out.println(e);
System.out.print("You're opening too many servers in the same location, fool!\n");
ServerSocket srvr = new ServerSocket(port);
while (true) {
Socket skt = srvr.accept();
clientProcessingPool.submit(new ClientTask(skt));
}
} catch (IOException ex) {
Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
Thread serverThread = new Thread(serverTask);
serverThread.start();
}
private class ClientTask implements Runnable {
private final Socket skt;
private ClientTask(Socket skt) {
this.skt = skt;
}
#Override
public void run() {
//for sending messages
if (connected == false) {
System.out.println("======================");
System.out.println("Server has connected!");
processMessage(testMessage);
}
//for receiving messages
while (true) {
try {
// Read one line and output it
BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
String incomingMessage = br.readLine();
if (incomingMessage != null) {
System.out.println("Server: Received message: " + incomingMessage);
processMessage(incomingMessage);
}
//br.close();
//skt.close(); //maybe delete
} catch (Exception e) {
System.out.println("Server had error receiving message.");
System.out.println("Error: " + e);
}
}
}
//for processing a message once it is received
public void processMessage(String message) {
PrintWriter out = null;
try {
out = new PrintWriter(skt.getOutputStream(), true);
} catch (IOException ex) {
System.out.println(ex);
System.out.println("Server had error sending message.");
}
System.out.print("Server: Sending message: " + message + "\n");
out.print(message);
out.flush();
connected = true;
try {
skt.shutdownOutput();
//out.close();
} catch (IOException ex) {
Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
}
Client class code:
import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JOptionPane;
class Client {
public String message;
Socket skt;
public int port;
public Client(int port) {
this.port = port;
}
//for receiving messages from Server
public void receiveMessage() {
final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
Runnable serverTask = new Runnable() {
#Override
public void run() {
try {
skt = new Socket(InetAddress.getLocalHost().getHostName(), port);
while (true) {
clientProcessingPool.submit(new Client.ClientTask(skt));
}
} catch (IOException ex) {
Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
}
}
};
Thread serverThread = new Thread(serverTask);
serverThread.start();
}
//for sending messages to Server
public void sendMessage(String outgoingMessage) throws IOException {
try {
skt = new Socket(InetAddress.getLocalHost().getHostName(), port);
PrintWriter pw = new PrintWriter(skt.getOutputStream());
System.out.println("Client: Sending message: " + outgoingMessage);
pw.print(outgoingMessage);
pw.flush();
skt.shutdownOutput();
//skt.close(); //maybe delete
} catch (Exception e) {
System.out.println(e);
System.out.print("Client had error sending message.\n");
JOptionPane.showMessageDialog(null, "That User is not currently online.", "ERROR!!", JOptionPane.INFORMATION_MESSAGE);
}
}
private class ClientTask implements Runnable {
private final Socket skt;
private ClientTask(Socket skt) {
this.skt = skt;
}
#Override
public void run() {
while (true) {
try {
BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));
//while (!in.ready()) {}
String incomingMessage = in.readLine();
if (incomingMessage != null) {
System.out.println("Client: Received message: " + incomingMessage); // Read one line and output it
message = incomingMessage;
}
//skt.shutdownInput();
//in.close();
//skt.close(); //maybe delete
} catch (Exception e) {
System.out.print("Client had error receiving message.\n");
}
}
}
}
}

Streams cannot be re-wrapped. Once assigned to a wrapper, they must use that wrapper for the entire life-cycle of the stream. You also shouldn't close a stream until you are done using it, which in this case isn't until your client and server are done communicating.
In your current code, there are a few times where you re-initialize streams:
while (true) {
try {
//Each loop, this reader will attempt to re-wrap the input stream
BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
String incomingMessage = br.readLine();
if (incomingMessage != null) {
System.out.println("Server: Received message: " + incomingMessage);
processMessage(incomingMessage);
}
//don't close your stream and socket so early!
br.close();
skt.close();
} catch (Exception e) {
//...
}
You get the idea; you can use this knowledge to find the stream problems in your client code as well.
With that said, servers are the middle-man between multiple clients. If you want to be able to type in the server's console to send a message to clients, it shouldn't go to only 1 client (unless you had a system that allowed you to specify a name). You need to store every connection in some kind of collection so when you type in the server's console, it goes to every client that's connected. This also helps when a client wants to send a message to every other client (global message). The server's main thread is primarily for accepting clients; I created another thread to allow you to type in the console.
As for your streams, you should create them whenever you start the ClientTask, both server side and client side:
public class Server {
private ExecutorService executor = Executors.newFixedThreadPool(10);
private Set<User> users = new HashSet<>();
private boolean running;
private int port;
public Server(int port) {
this.port = port;
}
public void start() {
running = true;
Runnable acceptor = () -> {
try(ServerSocket ss = new ServerSocket(port)) {
while(running) {
User client = new User(ss.accept());
users.add(client);
executor.execute(client);
}
} catch(IOException e) {
//if a server is already running on this port;
//if the port is not open;
e.printStackTrace();
}
};
Runnable userInputReader = () -> {
try(Scanner scanner = new Scanner(System.in)) {
while(running) {
String input = scanner.nextLine();
for(User user : users) {
user.send(input);
}
}
} catch(IOException e) {
//problem sending data;
e.printStackTrace();
}
};
Thread acceptorThread = new Thread(acceptor);
Thread userThread = new Thread(userInputReader);
acceptorThread.start();
userThread.start();
}
public void stop() {
running = false;
}
public static void main(String[] args) {
new Server(15180).start();
System.out.println("Server started!");
}
}
In the run() method is where the streams should be wrapped.
class User implements Runnable {
private Socket socket;
private boolean connected;
private DataOutputStream out; //so we can access from the #send(String) method
public User(Socket socket) {
this.socket = socket;
}
public void run() {
connected = true;
try(DataInputStream in = new DataInputStream(socket.getInputStream())) {
out = new DataOutputStream(socket.getOutputStream());
while(connected) {
String data = in.readUTF();
System.out.println("From client: "+data);
//send to all clients
}
} catch(IOException e) {
//if there's a problem initializing streams;
//if socket closes while attempting to read from it;
e.printStackTrace();
}
}
public void send(String message) throws IOException {
if(connected) {
out.writeUTF(message);
out.flush();
}
}
}
It's pretty much the same idea with the client:
1. Connect to Server
2. Create "communication" thread
3. Create "user input" thread (to receive input from console)
4. Start threads
public class Client {
private final String host;
private final int port;
private boolean connected;
private Socket socket;
public Client(String host, int port) {
this.host = host;
this.port = port;
}
public void start() throws IOException {
connected = true;
socket = new Socket(host, port);
Runnable serverInputReader = () -> {
try (DataInputStream in = new DataInputStream(socket.getInputStream())) {
while (connected) {
String data = in.readUTF();
System.out.println(data);
}
} catch (IOException e) {
// problem connecting to server; problem wrapping stream; problem receiving data from server;
e.printStackTrace();
}
};
Runnable userInputReader = () -> {
try (DataOutputStream out = new DataOutputStream(socket.getOutputStream());
Scanner scanner = new Scanner(System.in)) {
while (connected) {
String input = scanner.nextLine();
out.writeUTF(input);
}
} catch (IOException e) {
//problem wrapping stream; problem sending data;
e.printStackTrace();
}
};
Thread communicateThread = new Thread(serverInputReader);
Thread userThread = new Thread(userInputReader);
communicateThread.start();
userThread.start();
}
public static void main(String[] args) throws IOException {
new Client("localhost", 15180).start();
}
}
There are a few things I used in the code above that you may not be familiar with. They help simplify the syntax for your code:
Lambda Expressions - Prevents the need to create an anonymous class (or subclass) to declare a method
Try-With-Resources - Closes the resources specified automatically once the try block as ended
EDIT
When a user connects, you should store their connection by name or id. That way, you can send data to specific users. Even if your client is running on the same machine as the server, it's still the same idea: client connects to server, server sends message to client based on name or id:
while(running) {
User client = new User(ss.accept());
users.add(client); //add to set
executor.execute(client);
}
Right now, you are simply adding users to a Set. There is currently no way to grab a specific value from this set. What you need to do is give it some kind of "key". To give you an idea, here's an old algorithm I used to use. I have an array full of empty slots. When someone connects, I look for the first empty slot. Once an empty slot is found, I pass the user the index of the array it's being stored at (that will be the user's id), then store the user in the array at the specified index. When you need to send a message to someone, you can use the id to access that specific array index, grab the user you want and send a message:
class Server {
private int maxConnections = 10;
private ExecutorService executor = Executors.newFixedThreadPool(maxConnections);
private User[] users = new User[maxConnections];
//...
while(running) {
Socket socket = ss.accept();
for(int i = 0; i < users.length; i++) {
if(users[i] == null) {
users[i] = new User(socket, i);
executor.execute(users[i]);
break;
}
}
}
//...
public static void sendGlobalMessage(String message) throws IOException {
for(User user : users)
if(user != null)
user.send(message);
}
public static void sendPrivateMessage(String message, int id) {
User user = users[id];
if(user != null) {
user.send(message);
}
}
}
class User {
private Socket socket;
private int id;
private DataOutputStream out;
public User(Socket socket, int id) {
this.socket = socket;
this.id = id;
}
public void send(String message) throws IOException {
out.writeUTF(message);
out.flush();
}
public void run() {
DataInputStream in;
//wrap in and out streams
while(connected) {
String data = in.readUTF();
//Server.sendGlobalMessage(data);
//Server.sendPrivateMessage(data, ...);
sendMessage(data); //sends message back to client
}
}
}

TCP server madness - Slow and Merged data

I recently started to make a 2d java game, now I began the TCP server, though the server runs insanely slow (Average of 2 seconds) and I can't figure out how to stop the input stream from metering all the data into one string. I would greatly appreciate it if someone is able to help me.
ServerCode:
package com.diedericksclan.main.network;
import java.io.*;
import java.net.*;
import java.util.ArrayList;
public class ServerThread extends Thread {
private ServerHandler server;
private ServerSocket dataSocket;
private Socket socket;
private InetSocketAddress address;
private int megabyte = 1024 * 1024;
private int dedicated = 1024;
public int RAM = megabyte * dedicated;
private WriteData send;
private ReadData read;
public ServerThread(ServerHandler server, String serverIP, int ram, int backlog) throws Exception {
this.server = server;
this.dedicated = ram;
//System.out.println(serverIP);
String ip = "localhost";
int port = 2048;
if(serverIP.contains(":")) {
ip = serverIP.split(":")[0];
port = Integer.parseInt(serverIP.split(":")[1]);
} else {
ip = serverIP;
port = 2048;
}
//System.out.println("Makin' the server");
this.dataSocket = new ServerSocket(port, backlog, InetAddress.getByName(ip));
this.address = new InetSocketAddress(dataSocket.getInetAddress(), port);
this.send = new WriteData();
this.read = new ReadData();
//System.out.println("Makin' the data handlers");
//System.out.println("Server has been made, details: " + address.getAddress() + ":" + address.getPort());
}
public ServerThread(ServerHandler server, String ip) throws Exception {
this(server, ip, 1024, 0);
}
public void run() {
//System.out.println("made");
this.send.start();
this.read.start();
while(true) {
try {
socket = dataSocket.accept();
socket.setReceiveBufferSize(megabyte);
socket.setSendBufferSize(megabyte);
socket.setTcpNoDelay(true);
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void sendData(byte[] data, InetAddress IPaddress, int port) {
this.send.sendData(data, IPaddress, port);
}
public void serverShutdown() {
try {
this.dataSocket.close();
if(this.socket != null) this.socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public class WriteData extends Thread {
public WriteData() {}
public void sendData(byte[] data, InetAddress IPaddress, int port) {
try {
System.out.println("[" + System.currentTimeMillis() + "] Sending... " + new String(data));
socket.getOutputStream().write(data);
socket.getOutputStream().flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public class ReadData extends Thread {
public ReadData() {}
public void run() {
try {
this.sleep(1000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
byte[] data;
while(true) {
try {
data = new byte[megabyte];
socket.getInputStream().read(data);
System.out.println("[" + System.currentTimeMillis() + "] Server has read, " + new String(data) + ", details: " + socket.getLocalAddress().getHostName() + ":" + socket.getLocalPort());
server.parsePacket(data, socket.getInetAddress(), socket.getPort());
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
ClientCode:
package com.diedericksclan.main.network;
import java.io.*;
import java.net.*;
public class ClientThread extends Thread {
private ClientHandler client;
private Socket socket;
private InetSocketAddress address;
private int megabyte = 1024 * 1024;
private WriteData send;
private ReadData read;
public ClientThread(ClientHandler client) {
this.client = client;
this.address = new InetSocketAddress("192.168.1.2", 2048);
socket = new Socket();
try {
socket.setSendBufferSize(megabyte);
socket.setSendBufferSize(megabyte);
socket.setTcpNoDelay(true);
socket.connect(address);
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
//System.out.println("Made client");
this.send = new WriteData();
this.read = new ReadData();
//System.out.println("Client has been made, details: " + socket.getLocalAddress() + ":" + socket.getLocalPort());
}
public void run() {
//System.out.println("made");
this.send.start();
this.read.start();
}
public void sendData(byte[] data) {
this.send.sendData(data);
}
public void serverShutdown() {
try {
this.socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public class WriteData extends Thread {
public WriteData() {}
public void sendData(byte[] data) {
try {
//System.out.println("[" + System.currentTimeMillis() + "] Sending... " + new String(data) + " to: " + socket.getInetAddress() + ":" + socket.getPort());
socket.getOutputStream().write(data);
socket.getOutputStream().flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public class ReadData extends Thread {
public ReadData() {}
public void run() {
byte[] data;
while(true) {
try {
data = new byte[megabyte];
socket.getInputStream().read(data);
System.out.println("[" + System.currentTimeMillis() + "] Server data recived, " + new String(data).trim());
client.parsePacket(data, socket.getInetAddress(), socket.getPort());
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
I did try to improve speed by making 2 separate threads for reading and writing data, in both the client and server, yet there was no improvement,

You have a few problems.
you allow any number of threads to write to the same socket at the same time. This makes developing a protocol very hard.
you need a protocol so you know where a message starts and end. e.g. you send the length first.
you ignore how many bytes where read. The minimum will be 1 and you can get any number of messages up to the size of the buffer at once. TCP is a stream protocol, not a messaging protocol.
If you have a reader and writer process on the same machine you should be able to get the latency to around 10 micro-seconds. (0.000010 seconds)
EDIT here is a simple example
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
public class PlainIOSample {
static final int RUNS = 1000000;
public static void main(String[] args) throws IOException {
ServerSocket ss = new ServerSocket(0);
DataSocket ds = new DataSocket(new Socket("localhost", ss.getLocalPort()));
DataSocket ds2 = new DataSocket(ss.accept());
long start = System.nanoTime();
for (int i = 0; i < RUNS; i++) {
// send a small message
ds.write(new byte[64]);
// receive the same message
byte[] bytes = ds2.read();
if (bytes.length != 64)
throw new AssertionError();
}
long time = System.nanoTime() - start;
System.out.printf("Average time to send/recv was %.1f micro-seconds%n",
time / RUNS / 1e3);
ds.close();
ds2.close();
}
static class DataSocket implements Closeable {
private final DataOutputStream dos;
private final DataInputStream dis;
private final Socket socket;
public DataSocket(Socket socket) throws IOException {
dos = new DataOutputStream(new BufferedOutputStream(socket.getOutputStream()));
dis = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
this.socket = socket;
}
public void write(byte[] message) throws IOException {
synchronized (dos) {
dos.writeInt(message.length);
dos.write(message);
dos.flush();
}
}
public byte[] read() throws IOException {
synchronized (dis) {
int length = dis.readInt();
byte[] bytes = new byte[length];
dis.readFully(bytes);
return bytes;
}
}
#Override
public void close() throws IOException {
socket.close();
}
}
}
prints
Average time to send/recv was 3.3 micro-seconds

Why are my sockets only able to communicate client-to-server and not server-to-client?

I have written a simple Java dispatcher with a daemon thread to handle the incoming traffic, and using another thread to send out commands.
The problem comes when the server receives the first message, then the client/server system gets stuck on where the server trying to send out a response to the client. The sockets on both end just simply freeze when the server sends out data.
I have simplified my original problem into a echo server and client; I guess I must have a very very stupid mistake on the code. The code and result on my machine are reproduced below. Can anyone explain what is going wrong?
Thanks!
Here is the results, we can see the server and client stuck once the first message received.
Echo Server listening port...
Echo Server: Waiting from client connection.
Connecting to the server.
Connected to the server.
Dispatcher send: 10
Dispatcher send: 11
Dispatcher send: 12
Dispatcher send: 13
Dispatcher read...
Dispatcher read...
Dispatcher readed 10
Code:
EchoTest:
import java.io.*;
import java.net.*;
public class EchoTest {
public static void main(String[] args) {
EchoServer.listen();
EchoClient client = new EchoClient();
EchoServer server = EchoServer.accept();
}
}
Client and Server:
class EchoClient implements Runnable {
private static final int PORT = 13244;
Socket socket;
Disp disp;
Thread client;
public EchoClient() {
client = new Thread(this);
client.start();
}
public void run() {
try {
System.out.println("Connecting to the server.");
Socket socket = new Socket("localhost", PORT);
System.out.println("Connected to the server.");
disp = new Disp(socket);
disp.send(10);
disp.send(11);
disp.send(12);
disp.send(13);
} catch(IOException e) {
System.out.println("Would not connect to local host: " + PORT);
System.exit(-1);
}
}
public void send(int m) {
disp.send(m);
System.out.println("Sent message " + m);
int echo = disp.getMsg();
if(m == echo) {
System.out.println("Message " + m + "sent and received.");
} else {
System.out.println("Message " + m + "cannot be echoed correctly.");
}
}
}
class EchoServer implements Runnable{
private static final int PORT = 13244;
private static ServerSocket serverSocket;
Disp disp;
public EchoServer(Socket s) {
disp = new Disp(s);
}
public static void listen() {
System.out.println("Echo Server listening port...");
try {
serverSocket = new ServerSocket(PORT);
} catch (IOException e) {
System.out.println("Could not listen on port: " + PORT);
System.exit(-1);
}
}
public static EchoServer accept(){
try {
System.out.println("Echo Server: Waiting from client connection.");
return new EchoServer(serverSocket.accept());
} catch(IOException e) {
System.out.println("Couldn't accept connection from client.");
System.exit(-1);
}
return null;
}
public void run() {
while(true) {
int m = disp.getMsg();
disp.send(m);
}
}
}
Disp:
class Disp implements Runnable{
int msg = -1;
Socket socket;
BufferedInputStream input;
DataInputStream dis;
BufferedOutputStream output;
DataOutputStream dos;
Thread daemon;
public Disp(Socket s) {
this.socket = s;
try{
input = new BufferedInputStream(socket.getInputStream());
dis = new DataInputStream(input);
output = new BufferedOutputStream(socket.getOutputStream());
dos = new DataOutputStream(output);
}catch(IOException e) {
}
daemon = new Thread(this);
daemon.start();
}
public void run() {
while(true) {
int m = get();
setMsg(m);
}
}
public void send(int m) {
synchronized(dos) {
try{
System.out.println("Dispatcher send: " + m);
dos.writeInt(m);
dos.flush();
} catch(IOException e) {
}
}
}
public int get() {
System.out.println("Dispatcher read...");
synchronized(dis) {
try{
int m = dis.readInt();
System.out.println("Dispatcher readed " + m);
return m;
} catch(IOException e) {
}
}
return -1;
}
synchronized public void setMsg(int m) {
while(true) {
if(msg == -1) {
try {
wait();
} catch(InterruptedException e) {
}
} else {
msg = m;
notifyAll();
}
}
}
synchronized public int getMsg() {
while(true) {
if(msg != -1) {
try {
wait();
} catch(InterruptedException e) {
}
} else {
notifyAll();
return msg;
}
}
}
}

That's an awful lot of code. First of all I suggest cutting it down.
Secondly, you never seem to call EchoServer.run, but it's difficult to see.

You should also set the TCP_NODELAY flag, as you send only a few bytes. The Operating system usually waits for more data before it sends a package (and your flush() has no influence over that behaviour, as flush only deals with java's buffers).