Develop Reference

Need help on Pi Calculation with single multiServer - (N)Clients programm on Java. (Sockets)

I am trying to make a single mutlithreaded Server , that many clients can connect. Every client takes his iD and a number of steps and tries to calculate Pi =3,14 with accuracy, after that every client sends its result back to Server and the Server Calculates the Final result finnaly prints Pi.
(Every Client works at the same time).
(We know from start how many Clients will connect)
So far I created the main Server , the ServerThread , and a ServerProtocol where every action is written there. A loop helps that many clients can connect. I gave as a string the specific number of client and the numSteps it has to calculate pi.
On the client side, I made the main Client and the ClientProtocol with the actions. So , the client take the string, make it integer and start calculating pi. At the end sends the result as a string and the Server makes it Integer and put it on an Array to calculate and print 3.14 .
So i am somewhere lost and can't find where , so any help will be aprecciated.
Server
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class ServerTCP {
private static final int PORT = 1234;
public static String num;
public static Lock lock = new ReentrantLock();
public static int clientsSoFar=-1;
public static void main(String[] args) throws IOException {
// server is listening on port
ServerSocket connectionSocket = new ServerSocket(PORT);
System.out.println("Server is listening to port: " + PORT);
// running infinite loop for getting client request
while(true) {
//Wait for connection and produce actual socket
Socket dataSocket = null;
// socket object to receive incoming client requests
dataSocket=connectionSocket.accept();
clientsSoFar++;
System.out.println("Received request from " + dataSocket.getInetAddress());
//Server Thread
ServerTCPThread sthread = new ServerTCPThread(dataSocket);
sthread.start();
}
}
}
ServerThread
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.Socket;
import java.util.Arrays;
public class ServerTCPThread extends Thread{
public static int clientsSoFar;
private Socket dataSocket;
private InputStream is;
private BufferedReader in;
private OutputStream os;
private PrintWriter out;
private static final String EXIT = "!";
public ServerTCPThread(Socket socket)
{
dataSocket = socket;
try {
is = dataSocket.getInputStream();
in = new BufferedReader(new InputStreamReader(is));
os = dataSocket.getOutputStream();
out = new PrintWriter(os,true);
}
catch(IOException e) {
System.out.println("I/O Error " + e);
}
}
public void run() {
int clientsP =2;
int numSteps=100;
String p = "2 100";
String inmsg, outmsg;
try {
//epeksergasia
String num1 = String.valueOf(ServerTCP.clientsSoFar);
String num2 = String.valueOf(numSteps/clientsP);
ServerTCP.num =num1+" "+num2;
//epeksergasia
int numClient;
String[] splited = p.split("\\s+");
numClient=Integer.parseInt(splited[0]);
ServerTcpProtocol app = new ServerTcpProtocol();
outmsg = app.message();
out.println(outmsg);
inmsg = in.readLine();
outmsg = app.processRequest(inmsg);
// while(!EXIT.equals(inmsg)) {
// outmsg = app.processRequest(inmsg);
//out.println(outmsg);
//inmsg = in.readLine();
// }
double outMsgDouble = Double.parseDouble(outmsg);
double [] pin = new double[clientsP];
Arrays.fill(pin, 0);
ServerTCP.lock.lock();
for (int i=0; i<clientsP; i++)
if (pin[i]==0)
pin[i]=outMsgDouble;
ServerTCP.lock.unlock();
dataSocket.close();
}
catch (IOException e) {
System.out.println("I/O Error --> " + e);
}
}
}
ServerProtocol
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class ServerTcpProtocol {
public String processRequest(String theInput) {
System.out.println("Received message from client: " + theInput);
String theOutput = theInput;
//System.out.println("Send message to client: " + theOutput);
return theOutput;
}
BufferedReader user = new BufferedReader(new InputStreamReader(System.in));
public String message() throws IOException {
System.out.println("Send number to Client: "+ ServerTCP.num);
//String theOutput = user.readLine();
String theOutput=ServerTCP.num;
//SimpleServerTCP.p="+1";
return theOutput;
}
}
Client
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.Socket;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class ClientTCP {
//Client should know servers address/name
private static final String HOST = "localhost";
private static final int PORT = 1234;
private static final String EXIT = "!";
public static double sum;
public static Lock lock = new ReentrantLock();
public static void main(String[] args) throws IOException {
//Try to connect to server
Socket dataSocket = new Socket(HOST, PORT);
//Set up input and output streams
InputStream is = dataSocket.getInputStream();
BufferedReader in = new BufferedReader(new InputStreamReader(is));
OutputStream os = dataSocket.getOutputStream();
PrintWriter out = new PrintWriter(os, true);
System.out.println("Connection to " + HOST + " established.");
//Send request and then receive and process reply
String inmsg, outmsg;
ClientTcpProtocol app = new ClientTcpProtocol();
inmsg = in.readLine();
System.out.println("Time to send back to Server");
outmsg = app.answere(inmsg);
out.println(outmsg);
//Socket close
dataSocket.close();
System.out.println("Data Socket closed.");
}
}
ClientProtocol
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class ClientTcpProtocol {
BufferedReader user = new BufferedReader(new InputStreamReader(System.in));
//Request comes from user input
public String prepareRequest() throws IOException {
System.out.print("Enter message to send to server:");
String theOutput = user.readLine();
return theOutput;
}
//Reply goes to user screen
public void processReply(String theInput) throws IOException {
System.out.println("Message received from server: " + theInput);
}
public String answere(String theInput) {
System.out.println("Received message from Server: " + theInput);
//String theOutput = theInput;
int myId;
double result=0;
int myStart=1;
int myStop;
int numStep;
double table= 0;
int numStep0;
int numStep1;
int numStep2;
int numStep3;
int numStep4;
//Input split
String[] splited = theInput.split("\\s+");
myId = Integer.parseInt(splited[0]);
numStep=Integer.parseInt(splited[1]);
myStop=numStep;
double step = 1.0 / (double)numStep;
ClientTCP.lock.lock();
try {
for(int i = myStart; i < myStop; i++) {
double x = ((double)i+0.5)*step;
table += 4.0/(1.0+x*x);
}
//Maybe this oart should be at the end of Server before calculation???
result = result + ( table * step);
String theOutput = Double.toString(result);
System.out.println("Send p to Server:" + theOutput);
return theOutput;
}finally {
ClientTCP.lock.unlock();
}
}
}

java.io.EOFException when using sockets with blockchain in java

i have to do a practice in my uni, it must create a blockchain using sockets and serialization in a "simple way". But when exiting the loop (typing "NO") It creates a EOF exception that i cannot solve, while closing the socket(s.close()). i would appreciate some help, i am not vry good at java. here are my classes.
Client
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
public class Client implements Runnable{
public static void main(String[] args) throws Exception {
(new Thread(new Client())).start();
}
public static MedicalReport createReport(){
return new MedicalReport(10,"pepe","id","record");
}
#Override
public void run() {
// int port = 12345;
// String computer = "localhost";
try{
Socket s = new Socket("localhost", 12348);
ObjectOutputStream p = new ObjectOutputStream(s.getOutputStream());
ObjectInputStream in = new ObjectInputStream(s.getInputStream());
/* PrintWriter print = new PrintWriter(s.getOutputStream());
print.println("ready");
print.flush();*/
//manda informe al servidor serializado y espera respuesta
boolean stop = false;
while(!stop){
try{
MedicalReport report = createReport();
p.writeObject(report);
p.flush();
p.reset();
System.out.println("Do you want to continue? Yes or No");
Scanner in1 = new Scanner (System.in);
String answer="";
if(in1.hasNextLine())
answer = in1.nextLine();
if(!answer.equalsIgnoreCase("yes")){
System.out.println(report);
stop = true;
}
}
catch(Exception e){
System.out.println(e);
}
}
try{
s.close();
}
catch(Exception e){
System.out.println(e);
}
}catch(Exception e){
System.out.println(e);
}
}
}
SERVER
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Scanner;
public class Server {
public static void main(String[] args)
throws Exception
{
ArrayList<Block> blockChain = new ArrayList<>();
try{
ServerSocket ss = new ServerSocket(12348);
Socket s = ss.accept();
ObjectOutputStream out = new ObjectOutputStream(s.getOutputStream());
ObjectInputStream in = new ObjectInputStream(s.getInputStream());
/* Scanner scanner = new Scanner(s.getInputStream());
String text = scanner.nextLine();*/
int i = 0;
int previousHash = 0;
while (i != 20){
MedicalReport rp = (MedicalReport)in.readObject();
Block block = new Block(rp,previousHash);
blockChain.add(block);
System.out.println("Block " + blockChain.size() + " added to blockchain");
System.out.println(blockChain.get(i));
previousHash = block.getBlockHash();
System.out.println(blockChain);
i++;
}
try{
ss.close();
}
catch(Exception e){
System.out.println(e);
}
}catch(Exception e){
System.out.println(e);
}
}
}
It looks like the error is while closing the socket, any idea?
EDIT REST OF THE CODE
MEDICAL REPORT
import java.io.Serializable;
public class MedicalReport implements Serializable {
private int age;
private String name;
private String id;
private String record;
private static final long serialVersionUID = 1L;
public MedicalReport(){super();}
public MedicalReport(int age, String name, String id, String record) {
super();
this.age = age;
this.name = name;
this.id = id;
this.record = record;
}
public String getRecord(){
return this.record;
}
public String toString(){
return this.name + ". \n" + this.age + ". \n" + this.id + ". \n" + this.record;
}
}
BLOCK
public class Block {
private int blockHash;
private int previousHash;
private MedicalReport report;
//Block Constructor.
public Block(MedicalReport report,int previousHash ) {
this.previousHash = previousHash;
this.report = report;
this.blockHash = report.hashCode();
}
public int getPreviousHash() {
return previousHash;
}
public MedicalReport getReport() {
return report;
}
public int getBlockHash() {
return blockHash;
}
}
EDIT 2
FIRST QUESTION SOLVED. Now i get this error when exiting the loop:
java.net.SocketException: Connection reset by peer: socket write error

readObject() throws EOFEzception when the peer has closed the connection. This is normal. Catch it and stop reading. There is no problem here to solve.

IMPORTANT: As EJP said EOFException is normal and you can control the flow of your code with it but if you still want to know how to do in the way you asked here it is. REMEMBER THIS IS JUST FULFILL YOUR QUESTION AND NOT ADVISED TO DO SO.
On Server Class
Replace
MedicalReport rp = (MedicalReport)in.readObject();
With
MedicalReport rp;
if((rp = (MedicalReport)in.readObject())==null) break;
On Client Class
ADD
p.writeObject(null);
Just above the s.close(); statement
You must know that when a peer close the connection normally then
read() returns -1,
readLine() returns null,
readXXX() throws EOFException for any other XXX
And A write will throw an IOException

objectInputStream.readObject() throws exception java.io.OptionalDataException

Can someone please resolve this issue.
Using JDK 1.8, I am trying to build a very simple chat application in Java using Sockets. In my client class as soon as following line executes
Message returnMessage = (Message) objectInputStream.readObject();
it throws exception.
Exception in thread "main" java.io.OptionalDataException
I am writing only objects of type Message to the stream and reading objects of type Message, since i wrote once, i dont think i am doing anything wrong in reading them in sequence.
Q. Also please let me know what is the best way to debug this type of application, how to hit the breakpoint in server while running client ?
Client
package com.company;
import sun.misc.SharedSecrets;
import java.io.*;
import java.net.Socket;
import java.net.UnknownHostException;
public class Client {
public static void main(String[] args) throws UnknownHostException, IOException, ClassNotFoundException{
Socket socket = new Socket("localhost", Server.PORT);
ObjectOutputStream objectOutputStream = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream objectInputStream = new ObjectInputStream(socket.getInputStream());
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
String readerInput = bufferedReader.readLine();
String[] readerInputTokens = readerInput.split("\u0020");
if(readerInputTokens.length != 2) {
System.out.println("Usage: Client <integer> <integer>");
} else {
Integer firstNumber = Integer.decode(readerInputTokens[0]);
Integer secondNumber = Integer.decode(readerInputTokens[1]);
Message message = new Message(firstNumber, secondNumber);
objectOutputStream.writeObject(message);
System.out.println("Reading Object .... ");
Message returnMessage = (Message) objectInputStream.readObject();
System.out.println(returnMessage.getResult());
socket.close();
}
}
public static boolean isInteger(String value) {
boolean returnValue = true;
try{Integer.parseInt(value);}
catch (Exception ex){ returnValue = false; }
return returnValue;
}
}
Server
package com.company;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public final static int PORT = 4446;
public static void main(String[] args) throws IOException, ClassNotFoundException {
new Server().runServer();
}
public void runServer() throws IOException, ClassNotFoundException {
ServerSocket serverSocket = new ServerSocket(PORT);
System.out.println("Server up & ready for connections ...");
// This while loop is necessary to make this server able to continuously in listning mode
// So that whenever a client tries to connect, it let it connect.
while (true){
Socket socket = serverSocket.accept(); // Server is ready to accept connectiosn;.
// Initialize Server Thread.
new ServerThread(socket).start();
}
}
}
Sever Thread
package com.company;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
public class ServerThread extends Thread {
private Socket socket = null;
ServerThread(Socket socket){
this.socket = socket;
}
public void run() {
try {
ObjectOutputStream objectOutputStream = new ObjectOutputStream(socket.getOutputStream());
objectOutputStream.writeChars("\n");
objectOutputStream.flush();
ObjectInputStream objectInputStream = new ObjectInputStream(socket.getInputStream());
Message message = (Message) objectInputStream.readObject();
multiplyNumbers(message);
System.out.println("Writing: "+message.toString());
objectOutputStream.writeObject(message);
System.out.println("Message Written");
socket.close();
} catch( IOException ex) {
ex.printStackTrace();
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
}
private void multiplyNumbers(Message message) {
message.setResult(message.getFirstNumber().intValue() * message.getSecondNumber().intValue());
}
}
Message Class
package com.company;
import java.io.Serializable;
public class Message implements Serializable {
private static final long serialVersionUID = -72233630512719664L;
Integer firstNumber = null;
Integer secondNumber = null;
Integer result = null;
public Message(Integer firstNumber, Integer secondNumber) {
this.firstNumber = firstNumber;
this.secondNumber = secondNumber;
}
public Integer getFirstNumber() {
return this.firstNumber;
}
public Integer getSecondNumber() {
return this.secondNumber;
}
public Integer getResult() {
return this.result;
}
public void setResult(Integer result) {
this.result = result;
}
#Override
public String toString() {
return "Message{" +
"firstNumber=" + firstNumber +
", secondNumber=" + secondNumber +
", result=" + result +
'}';
}
}

objectOutputStream.writeChars("\n");
Why are you writing a newline to an ObjectOutputStream? You're never reading it. Don't do that. Remove this wherever encountered.

Socket sends message only once

Code below works and sends message at scheduled time but I think it isn't a good solution to open new socket every time timer executes scheduled task. What I would like is to open socket in run method only once and access it in SendMessage class whenever new instance of class is made in timer. That way it doesn't work, it only sends one message and then stops sending. Also I would be happy for some critics about code or tips for making it thread safe.
public class Client implements Runnable{
// Client Constructor here
#Override
public void run(){
//SENDS ONLY ONE MESSAGE
pitcherSocket = new Socket(InetAddress.getByName(hostname), port);
Timer timer = new Timer();
timer.schedule(new SendMessage(), 0, 1000/mps);
}
private class SendMessage extends TimerTask{
private int id;
#Override
public void run() {
try
{ // THIS WORKS FINE, SENDS MESSAGES AT SCHEDULED TIME
pitcherSocket = new Socket(InetAddress.getByName(hostname), port);
OutputStream outToServer = pitcherSocket.getOutputStream();
DataOutputStream out = new DataOutputStream(outToServer);
out.writeInt(id);
out.flush();
}catch(IOException e)
{
e.printStackTrace();
}
}
}
}
EDIT: WHOLE CODE
CLIENT
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
public class Pitcher implements Runnable{
private int port;
private int mps;
private int size;
private String hostname;
private List<Integer> messageIds = Collections.synchronizedList(new ArrayList<Integer>());
private Socket pitcherSocket;
//constatns, integer is 4 bytes, long is 8 bytes
private static final int INT_SIZE = 4;
private static final int LONG_SIZE = 8;
public Pitcher(int port, int mps, int size, String hostname) {
this.port = port;
this.mps = mps;
this.size = size;
this.hostname = hostname;
}
#Override
public void run(){
System.out.println("Pitcher running...");
System.out.println();
Timer timer = new Timer();
timer.schedule(new SendMessage(), 0, 1000/mps);
timer.schedule(new DisplayStatistics(), 0, 1000/mps);
}
//Nested class that sends messages
private class SendMessage extends TimerTask{
private int numberOfSentMessages = 0;
private int id;
#Override
public void run() {
try {
pitcherSocket = new Socket(InetAddress.getByName(hostname), port);
OutputStream outToServer = pitcherSocket.getOutputStream();
DataOutputStream out = new DataOutputStream(outToServer);
//send message size
out.writeInt(size);
//message id is same as number of the sent message
id = numberOfSentMessages + 1;
out.writeInt(id);
messageIds.add(id);
//get system timestamp
long currentTimestamp = System.currentTimeMillis();
out.writeLong(currentTimestamp);
//fill in the rest-
byte[] rest = new byte[size - 2 * INT_SIZE - LONG_SIZE]; //message size(default 300 bytes) - size(4 bytes) - message id(4 bytse) - timestamp(8 bytes)
out.write(rest);
out.flush();
numberOfSentMessages++;
InputStream inFromServer = pitcherSocket.getInputStream();
DataInputStream in = new DataInputStream(inFromServer);
Integer catcherMessageSize = in.readInt();
Integer catcherId = in.readInt();
long catcherTimestamp = in.readLong();
System.out.println("Sent message: " + size + " " + id + " " + currentTimestamp + "...");
System.out.println("Received message: " + catcherMessageSize + " " + catcherId + " " + catcherTimestamp + "...");
System.out.println();
}catch(IOException e)
{
e.printStackTrace();
}
}
}
}
SERVER
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketTimeoutException;
public class Catcher implements Runnable{
private int port;
private String bind;
private ServerSocket serverSocket;
//constatns, integer is 4 bytes, long is 8 bytes
private static final int INT_SIZE = 4;
private static final int LONG_SIZE = 8;
public Catcher(int port, String bind) {
this.port = port;
this.bind = bind;
}
#Override
public void run() {
System.out.println("Catcher running...");
System.out.println();
try {
serverSocket = new ServerSocket(port, 100, InetAddress.getByName(bind));
}
catch (IOException e1) {
e1.printStackTrace();
}
while(true){
try
{
Socket server = serverSocket.accept();
DataInputStream in = new DataInputStream(server.getInputStream());
Integer pitcherMessageSize = in.readInt();
Integer pitcherId = in.readInt();
long pitcherTimestamp = in.readLong();
DataOutputStream out = new DataOutputStream(server.getOutputStream());
//message id and size are sent back
out.writeInt(pitcherMessageSize);
out.writeInt(pitcherId);
//send back current time
long currentTimestamp = System.currentTimeMillis();
out.writeLong(currentTimestamp);
//fill in the rest
byte[] rest = new byte[pitcherMessageSize - 2 * INT_SIZE - LONG_SIZE]; //message size(default 300 bytes) - size(4 bytes) - message id(4 bytes) - timestamp(8 bytes)
out.write(rest);
out.flush();
System.out.println("Received message: " + pitcherMessageSize + " " + pitcherId + " " + pitcherTimestamp + "...");
System.out.println("Sent message: " + pitcherMessageSize + " " + pitcherId + " " + currentTimestamp + "...");
System.out.println();
//server.close();
}
catch(SocketTimeoutException s){
System.out.println("Socket timed out!");
break;
}
catch(IOException e){
e.printStackTrace();
break;
}
}
}
}

Have you thought about making both socket and the DataOutputStream member variables of SendMessage. This is some code to give you a rough start. You will probably want to put some enhancements like checking whether the socket is open and being able to create a new one if the current one is closed...
private class SendMessage extends TimerTask {
private int id = 10;
private Socket pitchSocket;
private DataOutputStream out;
public SendMessage(Socket socket) {
this.pitchSocket = socket;
try{
out = new DataOutputStream(pitchSocket.getOutputStream());
} catch(IOException e) {
e.printStackTrace();
}
}
#Override
public void run() {
try {
out.writeInt(id);
out.flush();
} catch(IOException e) {
e.printStackTrace();
}
}
}

After being able to view the whole code I think that you definitely have some threading issues, though I think they are more heavily on the server side rather than the client side. Your server is single threaded. That means that you can only deal with one request at a time. You want a multithreaded server. I've refactored your code to create an example of Catcher which is multithreaded. I'm using the Thead class to do all of this which may be a little old fashioned. You might want to take a look at java.util.concurrent, they will probably have a more up to date.
package clientserver;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketTimeoutException;
public class Catcher implements Runnable{
private int port;
private String bind;
private ServerSocket serverSocket;
public Catcher(int port, String bind) {
this.port = port;
this.bind = bind;
}
#Override
public void run() {
System.out.println("Catcher running...");
System.out.println();
try {
serverSocket = new ServerSocket(port, 100, InetAddress.getByName(bind));
}
catch (IOException e1) {
e1.printStackTrace();
}
while(true){
try
{
new Thread(new CatcherHandler(serverSocket.accept())).start();
Thread.sleep(1000);
}
catch(SocketTimeoutException s){
System.out.println("Socket timed out!");
break;
}
catch(IOException e){
e.printStackTrace();
break;
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static void main(String[] argv){
new Thread( new Catcher(8093, "localhost")).start();;
}
}
class CatcherHandler implements Runnable{
Socket server;
DataOutputStream out;
DataInputStream in;
private static final int INT_SIZE = 4;
private static final int LONG_SIZE = 8;
public CatcherHandler(Socket server) {
super();
this.server = server;
try {
in = new DataInputStream(server.getInputStream());
out = new DataOutputStream(server.getOutputStream());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
#Override
public void run() {
try{
if(in.available() > 0){
Integer pitcherMessageSize = in.readInt();
Integer pitcherId = in.readInt();
long pitcherTimestamp = in.readLong();
//message id and size are sent back
out.writeInt(pitcherMessageSize);
out.writeInt(pitcherId);
//send back current time
long currentTimestamp = System.currentTimeMillis();
out.writeLong(currentTimestamp);
//fill in the rest
byte[] rest = new byte[pitcherMessageSize - 2 * INT_SIZE - LONG_SIZE]; //message size(default 300 bytes) - size(4 bytes) - message id(4 bytes) - timestamp(8 bytes)
out.write(rest);
out.flush();
System.out.println("Received message: " + pitcherMessageSize + " " + pitcherId + " " + pitcherTimestamp + "...");
System.out.println("Sent message: " + pitcherMessageSize + " " + pitcherId + " " + currentTimestamp + "...");
System.out.println();
Thread.sleep(1000);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{}
//server.close();
}
}
Additionally I refactored your client to be able to use one socket and be tread safe. Now SendMessage takes in a DataInputStream and a DataOutputSteam as it's arguments.
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
public class Pitcher implements Runnable{
private int port;
private int mps;
private int size;
private String hostname;
private List<Integer> messageIds = Collections.synchronizedList(new ArrayList<Integer>());
private Socket pitcherSocket;
private DataOutputStream out;
private DataInputStream in;
//constatns, integer is 4 bytes, long is 8 bytes
private static final int INT_SIZE = 4;
private static final int LONG_SIZE = 8;
public Pitcher(int port, int mps, int size, String hostname) {
this.port = port;
this.mps = mps;
this.size = size;
this.hostname = hostname;
try {
this.pitcherSocket = new Socket(InetAddress.getByName(hostname), port);
out = new DataOutputStream(pitcherSocket.getOutputStream());
in = new DataInputStream(pitcherSocket.getInputStream());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(String[] argv) throws Exception{
for(int i = 0; i < 10; i++){
new Thread(new Pitcher(8093, 1, 200, "localhost")).start();
Thread.sleep(1000);
}
Thread.sleep(10000);
}
#Override
public void run(){
System.out.println("Pitcher running...");
System.out.println();
Timer timer = new Timer();
timer.schedule(new SendMessage(out, in), 0, 1000);
//timer.schedule(new DisplayStatistics(), 0, 1000);
}
//Nested class that sends messages
private class SendMessage extends TimerTask{
private int numberOfSentMessages = 0;
private int id;
private DataOutputStream out;
private DataInputStream in;
public SendMessage(DataOutputStream out, DataInputStream in){
this.out = out;
this.in = in;
}
#Override
public void run() {
try {
long currentTimestamp = 0L;
synchronized(out){
//send message size
out.writeInt(size);
//message id is same as number of the sent message
id = numberOfSentMessages + 1;
out.writeInt(id);
messageIds.add(id);
//get system timestamp
currentTimestamp = System.currentTimeMillis();
out.writeLong(currentTimestamp);
//fill in the rest-
byte[] rest = new byte[size - 2 * INT_SIZE - LONG_SIZE]; //message size(default 300 bytes) - size(4 bytes) - message id(4 bytse) - timestamp(8 bytes)
out.write(rest);
out.flush();
}
numberOfSentMessages++;
long catcherTimestamp = 0L;
Integer catcherMessageSize;
Integer catcherId;
synchronized(in){
catcherMessageSize = in.readInt();
catcherId = in.readInt();
catcherTimestamp = in.readLong();
}
System.out.println("Sent message: " + size + " " + id + " " + currentTimestamp + "...");
System.out.println("Received message: " + catcherMessageSize + " " + catcherId + " " + catcherTimestamp + "...");
System.out.println();
Thread.sleep(1000);
}catch(IOException e)
{
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

The Java Socket class is not thread safe. To have multiple threads access the same Socket object you would need to synchronize their actions. This could be done by providing all your SendMessage-threads with a common object that would then act as a lock. You would need an object for each socket operation you are planning to use (e.g. read and write). Then, refactor every action that does a call to the Socket object into separate methods and synchronize them around that object. E.g. for the read operation you could have a method called read() inside SendMessage that calls Socket.read and synchronize this method around the lock-object for read.
private class SendMessage extends TimerTask{
private Object readLock;
private Socket socket;
public SendMessage(Object readLock, Socket socket) {
this.readLock = readLock;
this.socket = socket;
}
public void readFromSocket() {
synchronized(readLock) {
socket.read();
}
}
#Override
public void run() {
readFromSocket();
// do other stuff
}
}

How to create a java Server that accepts client connections and then build a relay connection for a client pair

I want to create a server that can accept multiple connections and then bind 2 clients as a pair and forward the data between these 2 clients. But it is about multiple pairs of clients. I already have multithread server that can create a new thread for each new connected client. The problem for me is that these threads dont know of each other and somehow I have to connect 2 clients to a connection pair.
For now I just create these pair connection as this: I wait for the first client, then I wait for the second client and then open a thread for the input of client 1 that gets forwarded to client 2 and the other way around. This is not usable for multiple clients.
How can I do this decent?

The way I see it, a client would need to
establish a TCP(?) connection with your server,
identify itself
give the ID of the other client it wishes to talk to
The first that connects would have to be kept on hold (in some global table in your server) until the second client connects.
Once a pair of clients would have been recognized as interlocutors, you would create a pair of threads to forward the data sent by each client to the other one.
UPDATE: Example
ClientSocket.java
package matchmaker;
import java.io.Closeable;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
public class ClientSocket implements Closeable {
private final Socket socket;
private final InputStream in;
private final OutputStream out;
private final String ownId;
private final String peerId;
public ClientSocket(Socket socket) throws IOException {
this.socket = socket;
this.in = socket.getInputStream();
this.out = socket.getOutputStream();
DataInputStream din = new DataInputStream(in);
this.ownId = din.readUTF();
this.peerId = din.readUTF();
}
public ClientSocket(String server, int port, String ownId, String peerId)
throws IOException {
this.socket = new Socket(server, port);
this.socket.setTcpNoDelay(true);
this.in = socket.getInputStream();
this.out = socket.getOutputStream();
this.ownId = ownId;
this.peerId = peerId;
DataOutputStream dout = new DataOutputStream(out);
dout.writeUTF(ownId);
dout.writeUTF(peerId);
}
public String getOwnId() {
return ownId;
}
public String getPeerId() {
return peerId;
}
public InputStream getInputStream() {
return in;
}
public OutputStream getOutputStream() {
return out;
}
#Override
public void close() throws IOException {
socket.close();
}
}
Matchmaker.java: the server
package matchmaker;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Matchmaker extends Thread {
private static final Logger LOG
= Logger.getLogger(Matchmaker.class.getName());
private final int port;
private final Map<ClientPair,ClientSocket> waiting = new HashMap<>();
public static void main(String[] args) {
try {
int port = 1234;
int st = 0;
for (String arg: args) {
switch (st) {
case 0:
switch (arg) {
case "-p":
st = 1;
break;
default:
System.out.println("Unknown option: " + arg);
return;
}
break;
case 1:
port = Integer.parseInt(arg);
st = 0;
break;
}
}
Matchmaker server = new Matchmaker(port);
server.start();
server.join();
} catch (InterruptedException ex) {
LOG.log(Level.SEVERE, null, ex);
}
}
private Matchmaker(int port) {
this.port = port;
setDaemon(true);
}
#Override
public void run() {
try {
ServerSocket server = new ServerSocket(port);
while (true) {
ClientSocket socket = new ClientSocket(server.accept());
ClientPair pair = new ClientPair(
socket.getOwnId(), socket.getPeerId());
ClientSocket other;
synchronized(this) {
other = waiting.remove(pair.opposite());
if (other == null) {
waiting.put(pair, socket);
}
}
if (other != null) {
LOG.log(Level.INFO, "Establishing connection for {0}",
pair);
establishConnection(socket, other);
} else {
LOG.log(Level.INFO, "Waiting for counterpart {0}", pair);
}
}
} catch (IOException ex) {
LOG.log(Level.SEVERE, null, ex);
}
}
private void establishConnection(ClientSocket socket, ClientSocket other)
throws IOException {
Thread thread = new StreamCopier(
socket.getInputStream(), other.getOutputStream());
thread.start();
thread = new StreamCopier(
other.getInputStream(), socket.getOutputStream());
thread.start();
}
}
StreamCopier.java: a thread that reads from an InputStream and writes to an OutputStream
package matchmaker;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.logging.Level;
import java.util.logging.Logger;
public class StreamCopier extends Thread {
private static final Logger LOG
= Logger.getLogger(StreamCopier.class.getName());
private final InputStream in;
private final OutputStream out;
public StreamCopier(InputStream in, OutputStream out) {
this.in = in;
this.out = out;
setDaemon(true);
}
#Override
public void run() {
LOG.info("Start stream copier");
try {
for (int b = in.read(); b != -1; b = in.read()) {
out.write(b);
}
} catch (IOException ex) {
LOG.log(Level.SEVERE, null, ex);
} finally {
LOG.info("End stream copier");
try {
out.close();
} catch (IOException ex) {
LOG.log(Level.SEVERE, null, ex);
}
}
}
}
ClientPair.java: a pair of client IDs
package matchmaker;
public class ClientPair {
private final String client1;
private final String client2;
public ClientPair(String client1, String client2) {
this.client1 = client1;
this.client2 = client2;
}
public String getClient1() {
return client1;
}
public String getClient2() {
return client2;
}
public ClientPair opposite() {
return new ClientPair(client2, client1);
}
#Override
public int hashCode() {
int hash = 5;
hash = 73 * hash + client1.hashCode();
hash = 73 * hash + client2.hashCode();
return hash;
}
#Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final ClientPair other = (ClientPair) obj;
return client1.equals(other.client1) && client2.equals(other.client2);
}
#Override
public String toString() {
return "[" + client1 + "," + client2 + "]";
}
}
ReaderClient.java: a sample client that reads from the socket and writes to standard output
package matchmaker;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.logging.Level;
import java.util.logging.Logger;
public class ReaderClient {
private static final Logger LOG = Logger.getLogger(ReaderClient.class.getName());
public static void main(String[] args) {
try (ClientSocket client
= new ClientSocket("localhost", 1234, "reader", "writer")) {
Reader reader
= new InputStreamReader(client.getInputStream(), "UTF-8");
BufferedReader in = new BufferedReader(reader);
for (String s = in.readLine(); s != null; s = in.readLine()) {
System.out.println(s);
}
} catch (IOException ex) {
LOG.log(Level.SEVERE, null, ex);
}
}
}
WriterClient.java: a sample client that writes to the socket
package matchmaker;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.logging.Level;
import java.util.logging.Logger;
public class WriterClient {
private static final Logger LOG = Logger.getLogger(ReaderClient.class.getName());
public static void main(String[] args) {
try (ClientSocket client
= new ClientSocket("localhost", 1234, "writer", "reader")) {
Writer writer
= new OutputStreamWriter(client.getOutputStream(), "UTF-8");
PrintWriter out = new PrintWriter(writer);
for (int i = 0; i < 30; ++i) {
out.println("Message line " + i);
}
out.flush();
} catch (IOException ex) {
LOG.log(Level.SEVERE, null, ex);
}
}
}