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Client-server two way communication

I wrote simple client serwer, but unfortunately, I did it so chaotic and poorly that I decided to write everything from scratch. I want to write to communicate in both directions with the ability to disconnect and connect a new client. It means the client or the server sends a message and an appropriate one reads it. At the beginning all works but when i want to close client i get two errors:
java.net.SocketException: Socket closed readSocketData()
java.net.SocketException: Socket closedwriteData(String data)
Of course I understand what those errors means , but I do not understand why they show up because i have a while loop in which i check if the client is connected. Later when i try to connect a new client everything is falling apart.
I wrote 3 classes client, server and communication. Client and server inherits from communication (methods for opening and reading data streams). It all looks like that:
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class Server extends Communication{
ServerSocket serverSocket;
Socket listener;
boolean listenerLife;
public Server(int port) {
try {
serverSocket = new ServerSocket(port);
} catch (IOException e) {
System.out.println(e);
}
}
public void startListener(){
while (true){
try {
listener = serverSocket.accept();
listenerLife = true;
} catch (IOException e) {
System.out.println(e);
}
openWriter(listener);
openReader(listener);
writeServerDataThread();
new Thread(new Runnable() {
#Override
public void run() {
readData();
}
}).start();
}
}
public void writeServerDataThread(){
openLocalReader();
new Thread(new Runnable() {
#Override
public void run() {
while (true){
String data = readLocalData();
writeData(data);
}
}
}).start();
}
public void readData(){
while (listenerLife){
String data = readSocketData();
if("exit".equals(data) || data == null){
try {
listenerLife = false;
listener.close();
} catch (IOException e) {
System.out.println(e);
}
}
else {
System.out.println(data);
}
}
}
public void writeData(String data){
try {
writer.writeBytes(data + '\n');
writer.flush();
} catch (IOException e) {
System.out.println(e);
}
}
public static void main(String[] args) {
Server server = new Server(8080);
server.startListener();
}
}
import java.io.IOException;
import java.net.Socket;
public class Client extends Communication{
Socket clientSocket;
boolean clientLive;
public Client(String hostName, int port) {
try {
clientSocket = new Socket(hostName, port);
clientLive = true;
} catch (IOException e) {
System.out.println(e + "Client(String hostName, int port)");
}
}
public boolean closeConnection(String data){
if("exit".equals(data) || data == null){
try {
writeData("Zamykam klienta");
clientSocket.close();
clientLive = false;
return false;
} catch (IOException e) {
System.out.println(e + "closeConnection(String data)");
}
}
return true;
}
public void readClientData(){
new Thread(new Runnable() {
#Override
public synchronized void run() {
openLocalReader();
while (!clientSocket.isClosed()){
String data = readLocalData();
if(closeConnection(data)){
writeData(data);
}
}
}
}).start();
}
public void readServerDataThread(){
new Thread(new Runnable() {
#Override
public synchronized void run() {
while (!clientSocket.isClosed()){
String data = readSocketData();
if(closeConnection(data)){
System.out.println(data);
}
}
}
}).start();
}
public void writeData(String data){
try {
writer.writeBytes(data + '\n');
writer.flush();
} catch (IOException e) {
System.out.println(e + "writeData(String data)");
}
}
public static void main(String[] args) {
final Client client = new Client("localhost", 8080);
client.openReader(client.clientSocket);
client.openWriter(client.clientSocket);
client.readServerDataThread();
client.readClientData();
}
}
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
public class Communication {
BufferedReader reader;
BufferedReader localReader;
DataOutputStream writer;
public void openReader(Socket incomingSocket){
try {
reader = new BufferedReader(new InputStreamReader(incomingSocket.getInputStream()));
} catch (IOException e) {
System.out.println(e);
}
}
public void openWriter(Socket incomingSocket){
try {
writer = new DataOutputStream(incomingSocket.getOutputStream());
} catch (IOException e) {
System.out.println(e);
}
}
public void openLocalReader(){
localReader = new BufferedReader(new InputStreamReader(System.in));
}
public String readLocalData(){
String data = null;
try {
data = localReader.readLine();
} catch (IOException e) {
System.out.println(e + " readLocalData()");
}
return data;
}
public String readSocketData(){
String data = null;
try {
data = reader.readLine();
} catch (IOException e) {
System.out.println(e + " readSocketData()");
}
return data;
}
}

java.net.SocketException: Socket closed readSocketData()
java.net.SocketException: Socket closed writeData(String data)
Of course I understand what those errors means
They mean you closed the socket and continued to use it.
but I do not understand why they show up because i have a while loop in which i check if the client is connected.
No you don't. You have a while loop in which you check if the client socket is still open, which isn't the same thing at all ... but in any case that doesn't prevent you from using a closed socket inside the loop, for example after you close it in closeConnection(), whose return value being back to front from what it should be is doubtless causing confusion, and which is called by two threads as far as I can tell.

KnockKnockServer in Java

I am newbie in java networking ,I am trying to make a server application in java called instant messaging without GUI. So whenever i run the program it says
" Main method not found in class Methods, please define the main method as:
public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application" -ECLIPSE
Please help me what's wrong in my code.
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
// FIRST FILE //
public class main{
public static void main (String[] args) {
Server s=new Server();
s.runningserver();
}
}
//SECOND FILE//
public class Server {
private ObjectOutputStream output;
private ObjectInputStream input;
private ServerSocket server;
private Socket connection;
//wait For Connection,then display connection information
private void waitforConnection() {
System.out.println("wait for Someone to Connect.....\n");
try {
connection=server.accept();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("error In Acceptance of Server!!\n...");
}
System.out.println(("Connection Established"+connection.getInetAddress().getHostName()));
}
//Setting Up Streams to Get Input and Output
private void setupStreams(){
try {
output=new ObjectOutputStream(connection.getOutputStream());
output.flush();
input=new ObjectInputStream(connection.getInputStream());
System.out.println("Your Streams are Perfectly Working...");
} catch (IOException e) {
// TODO Auto-generated catch block
System.err.println("Error Found! in Streaming Connectionos");
e.printStackTrace();
}
}
// While Chatting Method....!!//
private void whileChatting() throws IOException{
String Message="You are now Connected!!\n";
sendMessage(Message);
//abletoType(true);
do{
try{
Message=(String) input.readObject();
System.out.println("\n"+Message);
}
catch(ClassNotFoundException e ){
System.out.println("wtf---Fuck\n YOu\n Bloody\n HAcker!!!\n");
}
}
while(!Message.equals("CLIENT--END"));
}
// Closing All Streams and Socket after you are done//
private void closeCrap(){
System.out.println("\nClosing Connection...........Bye Bye\n");
//abletoType(false);
try {
output.close();
input.close();
connection.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("Couldn't Close Connections!");
}
}
//Sending Messages to Client
private void sendMessage(String message){
try {
output.writeObject("SERVER--- "+message);
output.flush();
System.out.println("\nServer- "+message);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("Dude I cant Send yeaah..");
}
}
// Setting up the Server
public void runningserver(){
try {
server=new ServerSocket(4444,100);
while(true){try{
//connect and Have connection
waitforConnection();
setupStreams();
whileChatting();
}
finally{
closeCrap();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

EDIT: Here is the solution and I checked it and for me it works (run the MainClass.java file!):
//MainClass.java file:
public class MainClass {
public static void main (String[] args) {
Server s=new Server();
s.runningserver();
}
}
//Server.java file:
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
private ObjectOutputStream output;
private ObjectInputStream input;
private ServerSocket server;
private Socket connection;
// wait For Connection,then display connection information
private void waitforConnection() {
System.out.println("wait for Someone to Connect.....\n");
try {
connection = server.accept();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("error In Acceptance of Server!!\n...");
}
System.out.println(("Connection Established" + connection
.getInetAddress().getHostName()));
}
// Setting Up Streams to Get Input and Output
private void setupStreams() {
try {
output = new ObjectOutputStream(connection.getOutputStream());
output.flush();
input = new ObjectInputStream(connection.getInputStream());
System.out.println("Your Streams are Perfectly Working...");
} catch (IOException e) {
// TODO Auto-generated catch block
System.err.println("Error Found! in Streaming Connectionos");
e.printStackTrace();
}
}
// While Chatting Method....!!//
private void whileChatting() throws IOException {
String Message = "You are now Connected!!\n";
sendMessage(Message);
// abletoType(true);
do {
try {
Message = (String) input.readObject();
System.out.println("\n" + Message);
} catch (ClassNotFoundException e) {
System.out.println("wtf---Fuck\n YOu\n Bloody\n HAcker!!!\n");
}
} while (!Message.equals("CLIENT--END"));
}
// Closing All Streams and Socket after you are done//
private void closeCrap() {
System.out.println("\nClosing Connection...........Bye Bye\n");
// abletoType(false);
try {
output.close();
input.close();
connection.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("Couldn't Close Connections!");
}
}
// Sending Messages to Client
private void sendMessage(String message) {
try {
output.writeObject("SERVER--- " + message);
output.flush();
System.out.println("\nServer- " + message);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("Dude I cant Send yeaah..");
}
}
// Setting up the Server
public void runningserver() {
try {
server = new ServerSocket(4444, 100);
while (true) {
try {
// connect and Have connection
waitforConnection();
setupStreams();
whileChatting();
} finally {
closeCrap();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
I can run that without an exception.
The Problem is your main method
public static void main (String[] args) {}
Is not in the class where you run it.
//separate file A.java
public class A
{}
//separate file B.java
public class B
{
public static void main (String[] args) {}
}
If you now run B, it works, because B.java has a main method. BUT: if you run A.java it says:
no main methode found. The file you want to run (A, B, etc. must have a main method defined)
If you run a java file, it will look for a main method (start point of execution).

The main method must be a method of the class:
import java.net.Socket;
public class Server {
public static void main (String[] args) {
Server s=new Server();
s.runningserver();
}
So it must come after the class declaration.

Server reply to Client message failing due to closed socket - Java Client-Server example

I'm creating this little client-server program to learn about sockets, and so far, I'm having a bit of trouble. For the purpose of this post, I consolidated the code into a single class. And the code will compile. (So it will show the same errors I get)
When the client connects to the server, the server socket properly creates a socket on the server-side. The Client then successfully sends a message to the server, but when the server tries to send a response to the client, there is an error saying the socket is closed.
Main.java
package main;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.BindException;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Hashtable;
public class Main {
boolean running = true;
public static void main(String[] args){
new Main().start();
}
public void start(){
new Thread(new ConnectionListener()).start(); //Starts Server
try {
connectToServer();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public class ConnectionListener implements Runnable{
public void run() {
ServerSocket ss = null;
try {
ss = new ServerSocket(31415);
}catch (BindException e) {
e.printStackTrace();
return;
} catch (IOException e) {
e.printStackTrace();
return;
}
while(running){
try {
Socket sock = ss.accept();
ServerConnection c = new ServerConnection(sock);
c.start();
} catch (IOException e) {
e.printStackTrace();
}
}
try {
ss.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void connectToServer() throws UnknownHostException, IOException{
//Create Connection to Server
Socket socket = new Socket("localhost",31415);
ClientConnection cc = new ClientConnection(socket);
cc.start();
//Send First Message to Server
Hashtable<Integer, String> htt = new Hashtable<Integer, String>();
htt.put(0,"Hello, This is a Chat Test");
Message m = new Message(Message.Type.CHAT,htt);
cc.sendMessage(m);
}
public class ServerConnection{
Socket sock;
boolean connected = true;
public ServerConnection(Socket sock){
this.sock = sock;
}
public void start() {
new Thread(new RequestListener()).start();
}
private void handleMessage(Message m){
System.out.println("Server : Handle message " + m.type.toString());
}
public void disconnect(){
System.out.println("Disconnect user");
}
public void sendMessage(Message m){
try {
ObjectOutputStream os = new ObjectOutputStream(sock.getOutputStream());
os.writeObject(m);
os.flush();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
class RequestListener implements Runnable{
public void run() {
ObjectInputStream is = null;
try {
is = new ObjectInputStream(sock.getInputStream());
while(connected){
try {
Message m = (Message)
is.readObject(); //EOFException
handleMessage(m);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}catch(SocketException e){
disconnect();
e.printStackTrace();
break;
}catch (IOException e) {
//e.printStackTrace(); //EOFException Here
}
}
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
is.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
public class ClientConnection {
private Socket socket;
private boolean connected = true;
public ClientConnection(Socket socket) {
this.socket = socket;
}
public void start(){
new Thread(new RequestListener()).start();
}
public void sendMessage(Message m){
try {
ObjectOutputStream os = new ObjectOutputStream(socket.getOutputStream());
os.writeObject(m);
os.flush();
os.close();
} catch (IOException e) {
System.out.println("Error Sending Message");
e.printStackTrace();
}
}
public void close() throws IOException{
Message m = new Message(Message.Type.DISCONNECT,null);
sendMessage(m);
socket.close();
}
private void handleMessage(Message m){
System.out.println("Client : Handle message " + m.type.toString());
}
class RequestListener implements Runnable{
public void run() {
ObjectInputStream is = null;
try {
System.out.println(socket.isConnected()); //true
System.out.println(socket.isClosed()); //false
InputStream iss = socket.getInputStream();
is = new ObjectInputStream(iss); //socketClosedException
while(connected){
try {
Message m = (Message)is.readObject();
handleMessage(m);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}catch(SocketException e){
System.out.println("Server Disconnected");
break;
}catch (IOException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
is.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
}
Message.java
package main;
import java.io.Serializable;
import java.util.Hashtable;
public class Message implements Serializable{
public enum Type{
LOGIN, PM, DISCONNECT, INCORRECT_LP,CORRECT_LP, UPDATE_USERLIST, CHAT, INCORRECT_VERSION
}
public Type type;
Hashtable ht;
public Message(Type type, Hashtable ht){
this.type = type;
this.ht = ht;
}
public Object get(Object o){
return ht.get(o);
}
}

There's nothing 'random' about it.
Closing the input or output stream of a Socket closes the other stream and the Socket.
In this case you are closing the ObjectOutputStream you have wrapped around the socket's output stream, which closes that output stream, which closes the socket's input stream and the socket.

ActiveMQ: How to get all messages in a queue for Receiver (Java)

Here is the Server's code:
import java.net.UnknownHostException;
import java.io.IOException;
import org.apache.activemq.transport.stomp.StompConnection;
public class Server{
public static void main(String[] args) {
try {
StompConnection con = new StompConnection();
con.open("localhost", 61618);
con.connect("admin", "admin123");
con.begin("a1");
con.send("/queue/test1", "This is test message 1");
con.send("/queue/test1", "This is test message 2");
con.send("/queue/test1", "This is test message 3");
con.commit("a1");
con.disconnect();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}
Here is the Client's code:
import java.io.IOException;
import java.net.UnknownHostException;
import java.util.Scanner;
import org.apache.activemq.transport.stomp.StompConnection;
import org.apache.activemq.transport.stomp.StompFrame;
import org.apache.activemq.transport.stomp.Stomp.Headers.Subscribe;
public class Client {
public static void main(String[] args) {
try {
//login.
Scanner in = new Scanner(System.in);
System.out.print("Password: ");
String pass = in.next();
if (!"123".equals(pass)){
System.out.println("Sorry, wrong password.");
}
else
{
StompConnection con= new StompConnection();
con.open("localhost", 61618);
con.connect("admin", "admin123");
con.subscribe("/queue/test1", Subscribe.AckModeValues.CLIENT);
con.begin("a2");
StompFrame mes = con.receive();
System.out.println(mes.getBody());
con.ack(message, "a2");
con.commit("a2");
con.disconnect();
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}
I have 3 messages on Server. However, I only can get 1 message per time in Client. How to get all the messages in the queue in a run? Anyone can help me?

Not entirely sure what you've tried here but to read all three is just a simple loop like:
con.begin("a2");
while (true) {
StompFrame message = null;
try {
message = connection.receive(5000);
} catch (Exception e) {
break;
}
System.out.println(mes.getBody());
con.ack(message, "a2");
}
connection.commit("a2");

Simple Java Threaded TCP Server thread

/*main method*/
Server server = new Server(tcpPort);
new Thread(server).start();
try {
Thread.sleep(1000*60); /* 60 seconds*/
} catch (InterruptedException e) {
e.printStackTrace();
}
server.stop;
...
This is the code I've written. A Server thread is started, and runs for 60 seconds. How do I change this to run infinitely, ending when a user enters Enter via a BufferedReader or something.
I've tried it with
while(!input.equals("")) { /* just pseudocoded here...*/
Thread.sleep(10);
}
but this will my Server stop from working correctly. My clients won't even connect to it anymore. Have I made a design mistake or is this an easy problem to solve?

Try this basic Chatting Server that I wrote. This server simply keeps running in loop and broadcast the message send by the clients to all the other clients associated with this server.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
public class Server {
// ///----------------------------------------Instance Variable Fields
ServerSocket ss = null;
Socket incoming = null;
// ///----------------------------------------Instance Variable Fields
// ///---------------------------------------- static Variable Fields
public static ArrayList<Socket> socList = new ArrayList<Socket>();
// ///---------------------------------------- static Variable Fields
public void go() {
try {
ss = new ServerSocket(25005);
while (true) {
incoming = ss.accept();
socList.add(incoming);
System.out.println("Incoming: " + incoming);
new Thread(new ClientHandleKaro(incoming)).start();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
ss.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
class ClientHandleKaro implements Runnable {
InputStream is = null;
OutputStream os = null;
InputStreamReader isr = null;
BufferedReader br = null;
PrintWriter pw = null;
boolean isDone = false;
Socket sInThread = null;
public ClientHandleKaro(Socket sxxx) {
this.sInThread = sxxx;
}
#Override
public void run() {
if (sInThread.isConnected()) {
System.out.println("Welcamu Clienta");
System.out.println(socList);
}
try {
is = sInThread.getInputStream();
System.out.println("IS: " + is);
isr = new InputStreamReader(is);
br = new BufferedReader(isr);
os = sInThread.getOutputStream();
pw = new PrintWriter(os, true);
String s = new String();
while ((!isDone) && (s = br.readLine()) != null) {
String[] asx = s.split("-");
System.out.println("On Console: " + s);
// pw.println(s);
Thread tx = new Thread(new ReplyKaroToClient(s,
this.sInThread));
tx.start();
if (asx[1].trim().equalsIgnoreCase("BYE")) {
System.out.println("I am inside Bye");
isDone = true;
}
}
} catch (IOException e) {
System.out.println("Thanks for Chatting.....");
} finally {
try {
Thread tiku = new Thread(new ByeByeKarDo(sInThread));
tiku.start();
try {
tiku.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Accha to hum Chalte hain !!!");
System.out.println(socList);
br.close();
pw.close();
sInThread.close();
} catch (IOException e) {
}
}
}
}
class ReplyKaroToClient implements Runnable {
public String mString;
public Socket mSocket;
public ReplyKaroToClient(String s, Socket sIn) {
this.mString = s;
this.mSocket = sIn;
}
#Override
public void run() {
for (Socket sRaW : socList) {
if (mSocket.equals(sRaW)) {
System.out.println("Mai same hun");
continue;
} else {
try {
new PrintWriter(sRaW.getOutputStream(), true)
.println(mString);
} catch (IOException e) {
System.out.println("Its in Catch");
}
}
}
}
}
class ByeByeKarDo implements Runnable {
Socket inCom;
public ByeByeKarDo(Socket si) {
this.inCom = si;
}
#Override
public void run() {
try {
new PrintWriter(inCom.getOutputStream(), true)
.println("You have Logged Out of Server... Thanks for ur Visit");
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
new Server().go();
}
}

Start with this SO thread: How to create a basic Java Server? . It will give you an example how to write a very simple server.
Key thing to note there is the serverSocket.accept() . It will block - in other words it will WAIT forever for a client to connect, or it will fail in the case of some error. Once a client is connected, you will get a clientSocket that you can use to read what client wrote, and also write to it.
It is really a good starting point for understanding Java network programming. However, I recommend you read more about this topic. Something like this: http://beej.us/guide/bgnet/