Develop Reference

Java Sockets sending multiple objects to the same server

I'm trying to send multiple Objects through a socket to a java server.
To have a gerneral type I convert my messages into an instance of the class Message and send this object to the server.
I wrote a little testclass, which sends three objects to the server.
The problem is, only one objects reaches the server.
I tried nearly everything, without success.
My Server:
public class Server {
private ServerConfig conf = new ServerConfig();
private int port = Integer.parseInt(conf.loadProp("ServerPort"));
Logger log = new Logger();
ServerSocket socket;
Chat chat = new Chat();
public static void main(String[] args) {
Server s = new Server();
if (s.runServer()) {
s.listenToClients();
}
}
public boolean runServer() {
try {
socket = new ServerSocket(port);
logToConsole("Server wurde gestartet!");
return true;
} catch (IOException e) {
logToConsole("Server konnte nicht gestartet werden!");
e.printStackTrace();
return false;
}
}
public void listenToClients() {
while (true) {
try {
Socket client = socket.accept();
ObjectOutputStream writer = new ObjectOutputStream(client.getOutputStream());
Thread clientThread = new Thread(new Handler(client, writer));
clientThread.start();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void logToConsole(String message) {
System.out.print(message);
}
public class Handler implements Runnable {
Socket client;
ObjectInputStream reader;
ObjectOutputStream writer;
User user;
public Handler(Socket client, ObjectOutputStream writer) {
try {
this.client = client;
this.writer = writer;
this.reader = new ObjectInputStream(client.getInputStream());
this.user = new User();
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void run() {
while (true) {
Message incomming;
try {
while ((incomming = (Message) reader.readUnshared()) != null) {
logToConsole("Vom Client: \n" + reader.readObject().toString() + "\n");
logToConsole(
"Vom Client: \n" + incomming.getType() + "-----" + incomming.getValue().toString());
handle(incomming);
}
} catch (SocketException se) {
se.printStackTrace();
Thread.currentThread().interrupt();
} catch (IOException ioe) {
ioe.printStackTrace();
Thread.currentThread().interrupt();
} catch (ClassNotFoundException e) {
e.printStackTrace();
Thread.currentThread().interrupt();
}
}
}
private void handle(Message m) throws IOException {
String type = m.getType();
if (type.equals(config.ConstantList.Network.CHAT.toString())) {
chat.sendMessage(m);
} else if (type.equals(config.ConstantList.Network.LOGIN.toString())) {
System.out.println(user.login(m.getValue().get(0), writer));
System.out.println(m.getValue().get(0));
}
}
}
}
The Client:
public class Connect {
Socket client = null;
ObjectOutputStream writer = null;
ObjectInputStream reader = null;
private Config conf = new Config();
//private String host = conf.loadProp("ServerIP");
String host = "localhost";
private int port = Integer.parseInt(conf.loadProp("ServerPort"));
public boolean connectToServer() {
try {
client = new Socket(host, port);
reader = new ObjectInputStream(client.getInputStream());
writer = new ObjectOutputStream(client.getOutputStream());
logMessages("Netzwerkverbindung hergestellt");
Thread t = new Thread(new MessagesFromServerListener());
t.start();
return true;
} catch (Exception e) {
logMessages("Netzwerkverbindung konnte nicht hergestellt werden");
e.printStackTrace();
return false;
}
}
public boolean isConnectionActive() {
if (client == null || writer == null || reader == null){
return false;
}else{
return true;
}
}
public void sendToServer(Message m) {
try {
writer.reset();
writer.writeUnshared(m);
writer.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
And I try to send the objects with the class:
public void sendChatMessage(String username, String message) throws InterruptedException {
ChatMessage cm = new ChatMessage();
cm.setChat(username, null, message);
Message m = new Message(cm);
conn.sendToServer(m);
System.out.println("SENDED");
}
public static void main(String[] args) throws InterruptedException {
String username = "testuser";
String chatmessage = "Hallo Welt!";
connect.connect();
sendChatMessage(username, chatmessage);
sendChatMessage(username, chatmessage);
sendChatMessage(username, chatmessage);
}
I know that this is always the same message, but it is only for test purposes.
The messages are the objects they are Serializable and with only one object it works as designed.
Does anyone can see where I made my mistake?

while ((incomming = (Message) reader.readUnshared()) != null) {
Here you are reading an object, and blocking until it arrives.
logToConsole("Vom Client: \n" + reader.readObject().toString() + "\n");
Here you are reading another object, and blocking till it arrives, and then erroneously logging it as the object you already read in the previous line.
Instead of logging reader.readObject(), you should be logging the value of incoming, which you have also misspelt.
And the loop is incorrect. readObject() doesn't return null at end of stream: it throws EOFException. It can return null any time you write null, so using it as a loop termination condition is completely wrong. You should catch EOFException and break.

Found the solution, the line logToConsole("Vom Client: \n" + reader.readObject().toString() + "\n"); in the Server class, blocks the connection.

How to write A ServerSocket which accept multiple clicent Socket?

I am working on Socket programming. I have build such a server which should accept multiple Clients. Here I have particular num of clients , clients keeps on sending msg to Server every 10sec , Server has to process it.The problem I am having is I am unable to connect multiple Server and here a single client is a continuous running programm in while(true) So if one client Sends a request another client can not connect . Here is my Program.
Server
public class SimpleServer extends Thread {
private ServerSocket serverSocket = null;
private Socket s1 = null;
SimpleServer() {
try {
serverSocket = new ServerSocket(1231);
this.start();
} catch (IOException ex) {
System.out.println("Exception on new ServerSocket: " + ex);
}
}
public void run() {
while (true) {
try {
System.out.println("Waiting for connect to client");
s1 = serverSocket.accept();
System.out.println("Connection received from " + s1.getInetAddress().getHostName());
InputStream s1In = s1.getInputStream();
DataInputStream dis = new DataInputStream(s1In);
String st = dis.readUTF();
System.out.println(st);
s1In.close();
dis.close();
s1.close();
// throw new ArithmeticException();
} catch (IOException ex) {
Logger.getLogger(SimpleServer.class.getName()).log(Level.SEVERE, null, ex);
}
catch (Exception e) {
System.out.println("Exceptiopn: "+e);
}
}
}
public static void main(String args[]) throws IOException {
new SimpleServer();
}
}
Server is working fine but I am not able to write Client program which shoud run in while(true) loop for sending msg to Server and allow other client also connect to Server.
but for a single client I write like this ,
public class SimClient extends Thread {
private Socket s1 = null;
SimClient() {
//this.start();
}
public void run() {
int i=0;
try {
s1 = new Socket("localhost", 1231);
} catch (IOException ex) {
Logger.getLogger(SimClient.class.getName()).log(Level.SEVERE, null, ex);
}
// while (i<10) {
try {
// Open your connection to a server, at port dfg1231
OutputStream s1out = s1.getOutputStream();
DataOutputStream dos = new DataOutputStream(s1out);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter Data from Client:");
String s = br.readLine();
dos.writeUTF(s);
dos.flush();
s1out.close();
dos.close();
// s1.close();
i++;
} catch (IOException ex) {
//ex.printStackTrace();
System.out.println("Exception in While: "+ex.getMessage());
}
//}
}
public static void main(String args[]) throws IOException {
SimClient s= new SimClient();
s.start();
}
}
So can any one help me to write client program. its a great help for me.

just as you have a Thread for the ServerSocket, you need to create a Thread for every Socket returned by serverSocket.accept() , then it loops back around immediately to block and wait to accept another Socket. Make a class called SocketHander which extends Thread and accepts a Socket in the constructor.
public class SocketHandler extends Thread {
private Socket socket;
public SocketHandler(Socket socket) {
this.socket = socket;
}
public void run() {
// use the socket here
}
}
and back in the ServerSocket handler...
for (;;) {
SocketHandler socketHander = new SocketHandler(serverSocket.accept());
socketHander.start();
}

It is generally a good idea to use a Fixed Size Thread Pool because creating Threads in a ad-hoc manner may cause the Server to run out of Threads if the requests are high.
public class SimpleServer extends Thread {
private ServerSocket serverSocket = null;
private static ExecutorService executor = Executors.newFixedThreadPool(100);
SimpleServer() {
try {
serverSocket = new ServerSocket(1231);
this.start();
} catch (IOException ex) {
System.out.println("Exception on new ServerSocket: " + ex);
}
}
public void run() {
while (true) {
try {
System.out.println("Waiting for connect to client");
final Socket s1 = serverSocket.accept();
executor.execute(new Runnable() {
public void run() {
try {
System.out.println("Connection received from " + s1.getInetAddress().getHostName());
InputStream s1In = s1.getInputStream();
DataInputStream dis = new DataInputStream(s1In);
String st = dis.readUTF();
System.out.println(st);
s1In.close();
dis.close();
s1.close();
} catch(Exception e) {
System.out.println("Exceptiopn: "+e);
}
// throw new ArithmeticException();
}});
} catch (IOException ex) {
Logger.getLogger(SimpleServer.class.getName()).log(Level.SEVERE, null, ex);
} catch (Exception e) {
System.out.println("Exceptiopn: "+e);
}
}
}
public static void main(String args[]) throws IOException {
new SimpleServer();
}
}

How to stop all instances of a thread

I'm developping a socket-based game in Java about riddles in a competitive way.
The server program creates a response thread besides other threads for each player (client), what I want to do is stop (or interrupt) all those response threads once a player sends the right response.
Here's my code
public class testReponse implements Runnable {
private Socket socket;
BufferedReader in;
PrintWriter out;
String reponse="";
public testReponse(Socket socket2){
socket = socket2;
}
#Override
public void run() {
while(!reponse.equals("right")){
try {
in = new BufferedReader (new InputStreamReader (socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream());
String reponse = in.readLine();
System.out.println("Reponse : "+ reponse);
if(reponse.equals("right")){
out.println("correct");
out.flush();
} else {
out.println("incorrect");
out.flush();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

It is not clear where is your server code is. However, the way I would do it is by having an AtomicBoolean as an instance variable in the server code. Once the "right" message is received from any of the clients, the value would change to false. In the code in the server side if you see that the value is false, then you stop!
This is one way to go about it but there might be better ways to do it though.
public class MyServer {
private AtomicBoolean keepServerOn = new AtomicBoolean(true);
public void setKeepServerOff() {
keepServerOn.set(false);
}
public void shouldKeepGoing() {
return keepServerOn.get();
}
public static void main(Strings[] args) {
....// where you accept clients and create TestResponse
MyServer myServer = new MyServer();
...// somewhere new TestResponse(socket, myServer);
}
}
public class testReponse implements Runnable {
private MyServer server;
private Socket socket;
private AtomicBoolean keepServerOn = new AtomicBoolean(true);
public testReponse(Socket socket2, MyServer server){
socket = socket2;
}
#Override
public void run() {
BufferedReader in = null;
PrintWriter out = null;
try {
in = new BufferedReader (new InputStreamReader (socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream());
while(server.shouldKeepGoing()){
String reponse = in.readLine();
System.out.println("Reponse : "+ reponse);
if(reponse.equals("right")){
server.setKeepServerOff();
out.println("correct");
out.flush();
} else {
out.println("incorrect");
out.flush();
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if(in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(out!= null) {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

Infinit Loop when socket client disconnect

I had implemented a Java Multithreading Socket Server. It's working fine and create a new thread for every new client connection. But I have a bug when the TCP connection is cutted by the client, the server enter in a infinit loop and i got this message for every loop:
ERROR : Bad Frame !!! : null
I tried to debug the execution and change the if else condition but always the same bug exist when a client disconnect.
Here is my server Code
public class TCPSockServer implements Runnable {
Socket sock;
static int counter = 0;
private static int TIMEOUT = 50000;
private static int MAX_TIMEOUT = 100000;
long lastReadTime;
public TCPSockServer(Socket sock) {
this.sock = sock;
}
public static void main(String[] args) {
try {
ServerSocket serverSock = new ServerSocket(12000);
System.out.println("TCPSockServer : Listening to PORT 12000 ...");
while (true) {
Socket newSock = serverSock.accept();
counter++;
InetAddress addr = newSock.getInetAddress();
System.out.println("TCPSockServer : Connection Number : "+ counter);
System.out.println("TCPSockServer : Connection made to "
+ addr.getHostName() + " : (" + addr.getHostAddress()
+ ")");
newSock.setSoTimeout(TIMEOUT);
newSock.setKeepAlive(true);
new Thread(new TCPSockServer(newSock)).start();
}
} catch (IOException e) {
System.err.println("Trackiz: Main : ERROR Connection Failed");
e.printStackTrace();
}
}
#Override
public void run() {
int clientID = counter;
try {
BufferedReader inStream = new BufferedReader(new InputStreamReader(
sock.getInputStream()));
StringBuilder inString = new StringBuilder();
String frame = null;
PrintStream outStream = new PrintStream(sock.getOutputStream());
while (true) {
if (inString.append((String) inStream.readLine()) == null) {
System.out.println("TCPSockServer : CLIENT NOT CONNECTED");
sock.close();
break;
} else {
lastReadTime = System.currentTimeMillis();
frame = inString.toString();
if (cond1(frame)) {
......
}else{
system.err.println("\nERROR : Bad Frame !!! : "+frame); // why it enter this else in an infinit loop
}
outStream.println(provt.sendCommand("TCPSockServer : ACK TO CLIENT"));
inString = null;
inString = new StringBuilder();
}
}
inStream.close();
outStream.close();
sock.close();
} catch (SocketTimeoutException e) {
if (!isConnectionAlive()) {
System.out.println("\nCONNECTION TERMINATED FROM CLIENT !"
+ clientID);
logger.log(Level.SEVERE, "TCPSockServer : Connection terminated with Client");
try {
sock.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
} else {
// TODO sendHeartBeat();
System.out.println("Sending HeartBeat ...");
}
e.printStackTrace();
} catch (IOException e) {
System.err.println("TCPSockServer : Connection Timeout. Try to reconnect !");
e.printStackTrace();
}
}
public boolean isConnectionAlive() {
return System.currentTimeMillis() - lastReadTime < MAX_TIMEOUT;
}
}

The append method will never return null, so this is not right, the if-branch will never be entered:
if (inString.append((String) inStream.readLine()) == null) {
The code should probably look more like this:
String line = inStream.readLine();
if (line == null) {
...
} else {
inString.append(line);
...
}

Java Client Server - Multiple Event Handling for the Client

I'm trying to setup a client server application using socket programming. My client connects to the server, but I'm unable to get the multiple event handling to work. My client applet has two text boxes and buttons associated with each one of of them. When I click button one, I was trying to get "Hello" to be displayed in the text box. When I click on button two, I was trying to get "Hello there" to be displayed in the second text box. However, only one value (the value I first click) shows up in both of the text boxes. Is my event handling mechanism incorrect? I am implementing the serializable interface and the client server communication deals with objects. Can someone please tell me what the problem in the code is? I haven't posted the ObjectCommunication.java code, but it simply implements the serializable interface and has the getter and setter (takes a string as an input parameter) method.
Many thanks!
The following is my server code:
import java.io.*;
import java.net.*;
public class Server_App {
public static void main(String[] args) {
try {
ServerSocket holder = new ServerSocket(4500);
for (;;) {
Socket incoming = holder.accept();
new ServerThread(incoming).start();
}
} catch (Exception e) {
System.out.println(e);
}
}
}
class ServerThread extends Thread
{
public ServerThread(Socket i) {
incoming = i;
}
public void run() {
try {
ObjectCommunication hold = new ObjectCommunication();
ObjectInputStream input = new ObjectInputStream(incoming.getInputStream());
ObjectOutputStream output = new ObjectOutputStream(incoming.getOutputStream());
hold = (ObjectCommunication) input.readObject();
if ((hold.getMessage()).equals("Event 1")) {
System.out.println("Message read: " + hold.getMessage());
hold.setMessage("Hello!");
} else if ((hold.getMessage()).equals("Event 2")) {
System.out.println("Message read:" + hold.getMessage());
hold.setMessage("Hello there!");
}
output.writeObject(hold);
input.close();
output.close();
incoming.close();
} catch (Exception e) {
System.out.println(e);
}
}
ObjectCommunication hold = null;
private Socket incoming;
}
The following is the client code:
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
public class Client_App extends Applet {
TextField textVal;
TextField anotherTextVal;
Socket socket;
ObjectCommunication hold = new ObjectCommunication();
ObjectCommunication temp = new ObjectCommunication();
ObjectOutputStream OutputStream;
ObjectInputStream InputStream;
public void init() {
socketConnection();
createGUI();
validate();
}
public void socketConnection() {
try {
socket = new Socket("127.0.0.1", 4500);
} catch (Exception e) {
System.out.println("Unknown Host");
}
try {
OutputStream = new ObjectOutputStream(socket.getOutputStream());
InputStream = new ObjectInputStream(socket.getInputStream());
} catch (IOException ex) {
System.out.println("Error: " + ex);
return;
}
}
public void createGUI() {
Button button = new Button("Hello Button");
add(button);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
button_actionPerformed(evt);
}
});
textVal = new TextField(6);
add(textVal);
Button anotherButton = new Button("Hello there Button");
add(anotherButton);
anotherButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
anotherButton_actionPerformed(evt);
}
});
anotherTextVal = new TextField(6);
add(anotherTextVal);
}
public void button_actionPerformed(ActionEvent e) {
String actionCommand = e.getActionCommand();
if (e.getSource() instanceof Button)
if (actionCommand.equals("Hello Button")) {
try {
temp.setMessage("Event 1");
//OutputStream.writeObject(temp);
new SendToServer().start();
new ListenToServer().start();
} catch (Exception ex) {
System.out.println("Communication didn't work!");
}
textVal.setText(hold.getMessage());
}
}
public void anotherButton_actionPerformed(ActionEvent evt) {
String action_Command = evt.getActionCommand();
if (evt.getSource() instanceof Button)
if (action_Command.equals("Hello there Button")) {
try {
temp.setMessage("Event 2");
new SendToServer().start();
new ListenToServer().start();
} catch (Exception ex) {
System.out.println("Communication didn't work!");
}
anotherTextVal.setText(hold.getMessage());
}
}
class ListenToServer extends Thread {
public void run() {
while (true) {
try {
hold = (ObjectCommunication) InputStream.readObject();
} catch (IOException e) {} catch (ClassNotFoundException e2) {}
}
}
}
class SendToServer extends Thread {
public void run() {
while (true) {
try {
OutputStream.writeObject(temp);
} catch (IOException e) {}
}
}
}
}

To be honest - I'm a little bit lazy to read through your code and seek there for a bug :) Nevertheless I'll post you here my snippet for socket-based multiple client-server application..
import java.net.*;
import java.io.*;
class ServeConnection extends Thread {
private Socket socket = null;
private BufferedReader in = null;
private PrintWriter out = null;
public ServeConnection(Socket s) throws IOException {
// init connection with client
socket = s;
try {
in = new BufferedReader(new InputStreamReader(
this.socket.getInputStream()));
out = new PrintWriter(this.socket.getOutputStream(), true);
} catch (IOException e) {
System.err.println("Couldn't get I/O.");
System.exit(1);
}
start();
}
public void run() {
System.out.println("client accepted from: " + socket.getInetAddress()
+ ":" + socket.getPort());
// get commands from client, until is he communicating or until no error
// occurs
String inputLine, outputLine;
try {
while ((inputLine = in.readLine()) != null) {
System.out.println("request: " + inputLine);
outputLine = inputLine;
out.println("I've recived "+outputLine);
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("server ending");
out.close();
try {
in.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
class Server {
public static void svr_main(int port) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(port);
} catch (IOException e) {
System.err.println("Could not listen on port: " + port);
System.exit(1);
}
System.out.println("Server ready");
try {
while (true) {
Socket socket = serverSocket.accept();
try {
new ServeConnection(socket);
} catch (IOException e) {
System.err.println("IO Exception");
}
}
} finally {
serverSocket.close();
}
}
}
class Client {
static Socket echoSocket = null;
static PrintWriter out = null;
static BufferedReader in = null;
public static void cli_main(int port, String servername) throws
IOException {
try {
echoSocket = new Socket(servername, port);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(
echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: " + servername);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for " + servername);
System.exit(1);
}
System.out.println("Client ready!");
while (true) {
inputLine = (in.readLine().toString());
if (inputLine == null) {
System.out.println("Client closing!");
break;
}
// get the input and tokenize it
String[] tokens = inputLine.split(" ");
}
out.close();
in.close();
echoSocket.close();
System.out.println("Client closing");
}
}
public class MyClientServerSnippet{
public static void main(String[] args) throws IOException {
if (args.length == 0) {
System.err.println("Client: java snippet.MyClientServerSnippet<hostname> <port>");
System.err.println("Server: java snippet.MyClientServerSnippet<port>");
System.exit(1);
}
else if (args.length > 1) {
System.out.println("Starting client...\n");
Client client = new Client();
client.cli_main(3049, "127.0.0.1");
} else {
System.out.println("Starting server...\n");
Server server = new Server();
server.svr_main(3049);
}
}
}
Hope this helps :] If anything would be ununderstandable, don't hesitate to ask for more details :)