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Is this the correct way to implement multithreading on Server side of concurrent client/server setup?

I have created this code snippet in both a single threaded version and multithreaded for a client/server setup I have going. I have tested both (recording the avg turn around time) and have gotten EXTREMELY similar results within margin of error when running multiple simple server commands at once. have I implememnted my client handler wrong?
This is my first time trying to implement a multithreaded server and from my understanding it just a matter of putting in a client handler being
`
class ServerThread extends Thread {
private Socket socket;
public ServerThread(Socket socket) {
this.socket = socket;
}
`
below is the snippet of the whole server code.
`
public class Server {
public static void main(String[] args) {
if (args.length < 1) return;
int port = Integer.parseInt(args[0]);
try (ServerSocket serverSocket = new ServerSocket(port)) {
System.out.println("Server is listening on port " + port);
while (true) {
Socket socket = serverSocket.accept();
System.out.println("New client connected");
new ServerThread(socket).start();
}
} catch (IOException ex) {
System.out.println("Server exception: " + ex.getMessage());
ex.printStackTrace();
}
}
}
class ServerThread extends Thread {
private Socket socket;
public ServerThread(Socket socket) {
this.socket = socket;
}
public void run() {
try {
InputStream input = socket.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(input));
OutputStream output = socket.getOutputStream();
PrintWriter writer = new PrintWriter(output, true);
String text;
do {
text = reader.readLine(); // reads text from client
Process p = Runtime.getRuntime().exec(text);
BufferedReader stdout = new BufferedReader(new InputStreamReader(p.getInputStream()));
String outputLine;
while ((outputLine = stdout.readLine()) != null) { // while serverMsg is not empty keep printing
writer.println(outputLine);
}
stdout.close();
writer.println("ENDCMD");
// Text here should just write back directly what the server is reading...?
}
while (!text.toLowerCase().equals("exit"));
socket.close();
} catch (IOException ex) {
System.out.println("Server exception: " + ex.getMessage());
ex.printStackTrace();
}
}
}
`

I have tested both (recording the avg turn around time) and have gotten EXTREMELY similar results within margin of error when running multiple simple server commands at once. have I implememnted my client handler wrong?
If you are not making a new connection for each command that you send, then this would be expected. Since each connection runs on one thread, a multi-threaded approach, as you have shown, would have the same speed as if you didn't make a new thread for each connection. The difference is that, without multi-threading, you can only have one connection at a time.

Java Server-Client Connection reset

I have server and client applications running on my local machine.
Client takes file, changes it and sends to server, then server responds if the file is correct. Client does it multiple times, sending one file at a time.
I send two files from client and on the second file I get Connection reset
Server snippet:
private void initServer() throws IOException {
while (true) {
ServerSocket server = new ServerSocket(55555);
Socket fromclient = server.accept();
InputStream sin = fromclient.getInputStream();
OutputStream sout = fromclient.getOutputStream();
DataInputStream in = new DataInputStream(sin);
DataOutputStream out = new DataOutputStream(sout);
String line = in.readUTF();
if (line.equals("new file")) {
long fileSize = in.readLong();
tempSavedFile = new File("/home/evgeniy/Files/Downloads/temp");
tempSavedFile.createNewFile();
try (FileOutputStream fos = new FileOutputStream(tempSavedFile)) {
int t;
for (int i = 0; i < fileSize; i++) {
t = sin.read();
fos.write(t);
}
}
if (checkPadding(tempSavedFile)) {
out.writeInt(PADDING_OK_RESPONSE);
} else {
out.writeInt(PADDING_ERROR_RESPONSE);
}
out.flush();
}
out.close();
in.close();
sout.close();
sin.close();
fromclient.close();
server.close();
}
}
Client class that calls new thread in for loop
for (byte i = 0; i < 2; i++) {
Callable callable = new FileSender(tempFile);
FutureTask<Integer> ftask = new FutureTask<>(callable);
Thread thread = new Thread(ftask);
thread.start();
int response = 3244;
try {
response = ftask.get();
} catch (InterruptedException | ExecutionException ex) {
Logger.getLogger(FXMLController.class.getName()).log(Level.SEVERE, null, ex);
}
putMessage(String.valueOf(response));
Client Callable thread:
public Integer call() throws Exception {
Socket socket = new Socket(address, serverPort);
InputStream sin = socket.getInputStream();
OutputStream sout = socket.getOutputStream();
DataInputStream in = new DataInputStream(sin);
DataOutputStream out = new DataOutputStream(sout);
out.writeUTF("new file");
out.flush();
out.writeLong(file.length);
out.flush();
sout.write(file);
sout.flush();
System.out.println(socket.isConnected());
int response = in.readInt();
System.out.println("--------RESP="+response);
out.close();
in.close();
sin.close();
sout.close();
socket.close();
return response;
}
As you can see I send two files, and get this console output on client app:
true
--------RESP=200
true
ноя 20, 2018 5:16:36 PM com.evgeniy_mh.paddingoracle.FXMLController SendFileToServer
SEVERE: null
java.util.concurrent.ExecutionException: java.net.SocketException: Connection reset
Also, I don't understand why socket is ok, but
int response = in.readInt();
raising Connection reset exception.

Your code creates a new ServerSocket and later closes the created server socket for every single request that it processes. The code does not use the same ServerSocket instance to serve multiple requests.
The connection reset failure appears to be because of this, as when the second request is creating a socket connection with the server, the existing ServerSocket is closed and recreated on the same port leading to the connection being reset. For a start try taking out the ServerSocket creation outside the while loop.
private void initServer() {
try (ServerSocket server = new ServerSocket(5555)) {
while (true) {
Socket fromclient = server.accept();
... // remaining code
fromclient.close();
}
} catch (IOException ioe) {
// handle failures
}
}
The try-with-resources handles the .close() call on the AutoCloseable server socket.
Also, note that the requests would be processed serially on a single thread in your code. Usually the Socket obtained for a connection from the ServerSocket#accept() (or the streams derived from it) is passed to a separate thread for processing unlike your code that processes the requests serially.

How to set a timeout on a BufferedReader with a socket stream

Here I am creating a thread to check for a server response every 2 seconds, the issue is that the client.monitorResponse() is a readLine() method and will not continue until a response is received.
client = new ClientObject("localhost");
timer.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
try {
String response = null;
if(!(response = client.monitorResponse()).isEmpty()) {
System.out.println("Response: " + response);
} catch (Exception e) {
e.printStackTrace();
}
}
}, 2000, 2000);
I am sending the response via the Server like so (where client is a established Socket):
public SocketObject(Socket client, int numberOfClients) throws Exception {
socket = client; // the .accept() socket is passed through
// this is because I assign them ID's for later use (I hold an ArrayList of sockets)
this.clientId = numberOfClients;
// both these are static to the class
outputStream = new PrintWriter(client.getOutputStream());
inputStream = new BufferedReader(new InputStreamReader(client.getInputStream()));
}
public void sendResponse(String response) {
outputStream.println(response);
}
I am then picking the response up via the client Socket that has connected to the server:
public ClientObject(String hostname) throws IOException {
// socket is static to this class
socket = new Socket(hostname, 4444);
System.out.println("Connected to " + hostname + " on port 4444...");
// both static to this class
outputStream = new PrintWriter(socket.getOutputStream(), true);
inputStream = new BufferedReader(new InputStreamReader(socket.getInputStream()));
System.out.println("Successfully started a stream on " + hostname);
this.hostname = hostname;
}
public String monitorResponse() throws Exception {
System.out.println("Listening for a response...");
return inputStream.readLine();
}
The debug console only displays the Listening for a response... output once which is telling me that it doesn't get past the inputStream.readLine() method in-side the Thread. Is there anyway I can add a timeout on the BufferedReader? I have tried multiple solutions like adding a .setSoTimeout() to the socket before creating the BufferedReader but all that did was close the connection/socket after the specified time.
Any help would be appreciated.

You should use a non-blocking (NIO) request and read chunks looking for newlines in-between. Typically in Java you just have to look for the NIO version of the Stream class you are using and use it to check every N seconds for new content. In your case with minimal modifications you can use the less fancy and efficient method of blocking calls with BufferedReader.ready() to prevent blocking:
String partialLine="";
public static String monitorResponse() throws Exception {
System.out.println("Listening for a response...");
int nextByte;
String nextChar;
while (inputStream.ready()) {
nextByte = inputStream.read();
nextChar = Character.toString ((char) nextByte);
partialLine += nextChar;
if ("\n".equals(nextChar)) {
String line = partialLine;
partialLine = "";
return line.replace("\r\n", "");
}
}
return "";
}
Check out http://tutorials.jenkov.com/java-nio/nio-vs-io.html for more info.

Is there anyway I can add a timeout on the BufferedReader?
No, but you can set a timeout on the Socket, with Socket.setSoTimeout().
I have tried multiple solutions like adding a .setSoTimeout() to the socket before creating the BufferedReader but all that did was close the connection/socket after the specified time.
No it doesn't close the socket. It throws SocketTimeoutException, which you should catch and handle as pertinent. If the socket is being closed, you're closing it. Solution: don't.

Unable to read and send the request simultaneously in java using serversocket

I have written this simple java server which is ready to accept connections on a port using server sockets.
I want that whenever some client tries to send some data on this port within same local network I want to:
1.print that data ie: read from inputstream using InputStreamReader into a buffer and then print into console.
2.send some data back to the client by writing on outputstream using OutPutStreamWriter.
3.close both the streams ie: outputStreamWriter and inputStreamReader and then finally close the socket.
The problem which I am facing is that I am able to do only one at a time even though I have created two separate threads for both input and output.
Example if I fire a request on port 8086 from any device within the same network everything gets blocked (mabye a deadlock) nothing is printed onto the console unless the client who made the request itself cancels the request.
similarly if I terminate the connection from server ie: terminate the java application then on the client side I get this response string "success".
I don't know why the streams are not getting closed after the process even though I have closed them.
I thought if we write onto outputstream and read in from inputstream in two different threads it would solve the problem but still no luck.
Can anybody help?
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
public class Notification {
private Socket clientSocket;
private BufferedReader buffInputStream;
private InputStreamReader inputStreamReader;
private OutputStreamWriter outputStreamWriter;
private OutputStream outputstream;
private InputStream inputstream;
public Notification(){
}
public void start() {
Thread listenThread = new Thread(listen);
listenThread.start();
}
Runnable listen = new Runnable() {
#Override
public void run() {
try {
ServerSocket serverSocket = new ServerSocket(8086);
while(true){
clientSocket = serverSocket.accept();
Thread t2 = new Thread(inStream);
t2.start();
Thread t1 = new Thread(outStream);
t1.start();
t1.join();
t2.join();
buffInputStream.close();
inputStreamReader.close();
outputStreamWriter.close();
clientSocket.close();
}
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}
}
};
Runnable outStream = new Runnable() {
#Override
public void run() {
try {
outputstream = clientSocket.getOutputStream();
outputStreamWriter = new OutputStreamWriter(outputstream);
outputStreamWriter.write("success");
outputStreamWriter.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
};
Runnable inStream = new Runnable() {
#Override
public void run() {
try {
inputstream = clientSocket.getInputStream();
inputStreamReader = new InputStreamReader(inputstream);
buffInputStream = new BufferedReader(inputStreamReader);
List<String> response = new ArrayList<>();
String line;
while ((line = buffInputStream.readLine()) != null) {
response.add(line);
}
String arr[] = response.toArray(new String[response.size()]);
for (String re : arr) {
System.out.println(re);
}
}
catch (IOException e){
e.printStackTrace();
}
}
};
}

There is no deadlock here. Your read thread simply isn't printing anything until the peer disconnects. Print each line as you read it, not after end-of-stream is received. You don't have any need for the list, or the array, or the second loop.
But this will never work. You're sharing a single clientSocket reference among all clients. You need to create Runnables that take the client socket as a parameter and store it as an instance variable.

Implementation of a simple file transfer client server

Hi I have the following code to the client - server through the thread, I have a errors,
Can't setup server on this port number.
Can't setup server on this port number.
but why?
class client:
import java.io.*;
import java.net.Socket;
// create class client
public class Client extends Thread {
Socket socket = null;
Socket socket1 = null;
// create send method
public void sendFile() throws IOException {
String host = "127.0.0.1";
String host1 = "127.0.0.2";
socket = new Socket(host, 4444);
socket1 = new Socket(host1, 444);
File file = new File("/home/reza/Desktop/link help");
File file1 = new File("/home/reza/Desktop/hi");
long length = file.length();
long length1 = file1.length();
byte[] bytes = new byte[(int) length];
byte[] bytes1 = new byte[(int) length1];
FileInputStream fis = new FileInputStream(file);
FileInputStream fis1 = new FileInputStream(file1);
BufferedInputStream bis = new BufferedInputStream(fis);
BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());
BufferedInputStream bis1 = new BufferedInputStream(fis1);
BufferedOutputStream out1 = new BufferedOutputStream(socket1.getOutputStream());
int count;
int count1;
while ((count = bis.read(bytes)) > 0) {
out.write(bytes, 0, count);
}
while ((count1 = bis1.read(bytes1)) > 0) {
out1.write(bytes1, 0, count1);
}
Thread t = new Thread(new Runnable() {
public void run()
{
while(socket.isConnected())
{
Wait2();
try {
sendFile();
} catch (IOException e) {
e.printStackTrace();
}
}
}
});
Thread t1 = new Thread(new Runnable() {
public void run() {
while(socket1.isConnected())
{
Wait2();
try {
sendFile();
} catch (IOException e) {
e.printStackTrace();
}
}
}
});
t.start();
t1.start();
fis.close();
fis1.close();
out.close();
bis.close();
out1.close();
bis1.close();
socket.close();
socket1.close();
}
public void Wait2()
{
try {
Thread.currentThread().sleep(3000);
} catch (InterruptedException x) {
System.out.println("Interrupted!");
}
}
}
// class server
import java.io.*;
import java.net.*;
public class Server {
public void recivefile() throws IOException {
ServerSocket serverSocket = null;
ServerSocket serverSocket1 = null;
try {
serverSocket = new ServerSocket(4444);
//serverSocket1 = new ServerSocket(444);
} catch (IOException ex) {
System.out.println("Can't setup server on this port number. ");
}
try {
serverSocket1 = new ServerSocket(444);
} catch (IOException ex) {
System.out.println("Can't setup server on this port number. ");
}
Socket socket = null;
Socket socket1 = null;
InputStream is = null;
InputStream is1 = null;
FileOutputStream fos = null;
FileOutputStream fos1 = null;
BufferedOutputStream bos = null;
BufferedOutputStream bos1 = null;
int bufferSize = 0;
int bufferSize1 = 0;
try {
socket = serverSocket.accept();
socket1 = serverSocket1.accept();
} catch (IOException ex) {
System.out.println("Can't accept client connection. ");
}
try {
is = socket.getInputStream();
is1 = socket1.getInputStream();
bufferSize = socket.getReceiveBufferSize();
bufferSize1 = socket1.getReceiveBufferSize();
System.out.println("Buffer size: " + bufferSize);
System.out.println("file recieved");
System.out.println("Buffer size1: " + bufferSize1);
System.out.println("file recieved");
System.out.println("file recieved");
} catch (IOException ex) {
System.out.println("Can't get socket input stream. ");
}
try {
fos = new FileOutputStream("/home/reza/Desktop/reza");
bos = new BufferedOutputStream(fos);
fos1 = new FileOutputStream("/home/reza/Desktop/ali");
bos1 = new BufferedOutputStream(fos1);
} catch (FileNotFoundException ex) {
System.out.println("File not found. ");
}
byte[] bytes = new byte[bufferSize];
int count;
while ((count = is.read(bytes)) > 0) {
bos.write(bytes, 0, count);
}
byte[] bytes1 = new byte[bufferSize1];
int count1;
while ((count1 = is1.read(bytes1)) > 0) {
bos1.write(bytes1, 0, count1);
}
bos.flush();
bos.close();
bos1.flush();
bos1.close();
is.close();
is1.close();
socket.close();
serverSocket.close();
socket1.close();
serverSocket1.close();
}
public static void main(String[] args) throws IOException
{
System.out.println("server is run, please send file");
Server s = new Server();
s.recivefile();
}
}
error is :
Can't setup server on this port number.
Can't setup server on this port number.

You can't start a server on 127.0.0.2 - therein lies your problem.

netstat -ano | find "1024"
try above command if you are running your java files on windows environment that will help you to find any process using same port no as yours and also use
ex.printStackTrace() along with
System.out.println("Can't setup server on this port number.");

Assuming that your code runs on a unix platform, your server code is trying twice to open a socket on port 444, which is a system reserved port. In order to be able to succeed, your programme must run with administrative priviledges, and you must ensure that the port is not already used by another process.
A possible workaround is to:
use a port above 1024. These ports are free to use for userland programmes
in case of failure have a backup port, also above 1024. You must amend both server and client codes to try both ports, and of course your communication protocol must include some form of handshaking to make sure they are talking to the right interlocutor.
There are many other problems with your code listed in other answers.
you don't need to make every objects twice. Only one instance is enough in most cases,
if your server is running continuously and must accept many connections, you should not close the accepting socket at the end of one receiving session.
also the server is supposed to run a loop on the server socket accept call, and start a new thread for each incoming connection, whose job is to handle that connection.
While I understand your willingness to learn and experiment, there are existing solutions to what you are trying to achieve. For instance, you could simply use a FTP server for your purpose.

The way you have written client - server program is wrong I guess.
Following are the mistakes you have done...
1) In Client class, you have sendFile function in which you've created two threads - t & t1. In run function you are again calling the same sendFile function.
So it keeps creating threads under threads just like recursion.
2) In Server class, you are listening to two port within the same recieveFile function. As the socket = serverSocket.accept() is a blocking call, It wont excecute the rest of the code untill it finds a single client to connect.
So what exactly happens here is.. Once the first client connects, thenafter immediately it expects second client to connect.
In the mean time your client thread may try to access the port on which connection has not been established.
In short, your SERVER SHOULD BE IN A THREADING ENVIRONMENT NOT THE CLIENT.
And I would suggest that for different port you should use different server.
i.e. create different server class for both 1024 & 1025 port.