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Java Socket Programming frame not responsive and loopy request

I'm trying socket programming for the first time and try codes from https://www.oracle.com/webfolder/technetwork/tutorials/obe/java/SocketProgramming/SocketProgram.html and implement it to a frame. Clients can connect to the server, but there are some problem with my server frame like it's not responsive. And the request handler is ok for the first use per client, and not working for the next request. I notice that the handler looks like having a loop which I don't know why it's happening.
How the server react when the request made
This is how I start the server
private void btnStartActionPerformed(java.awt.event.ActionEvent evt) {
try {
server = new ServerSocket(8005);
executor = Executors.newFixedThreadPool(5);
System.out.println("Waiting for clients");
while (true) {
socket = server.accept();
Runnable worker = new RequestHandler(socket);
executor.execute(worker);
System.out.println("check executor");
}
} catch (Exception e) {
System.out.println(e);
} finally{
if(executor!=null){
executor.shutdown();
}
}
}
The request handler
public class RequestHandler implements Runnable {
private Socket socket;
ServerSocket server = null;
public RequestHandler(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
try {
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
String userInput = in .readLine();
while (userInput != null) {
System.out.println("Received Message from " + Thread.currentThread().getName() + ": " + userInput);
jtaLog.append("Received Message from " + Thread.currentThread().getName() + ": " + userInput);
writer.write("You write : " + userInput);
writer.newLine();
writer.flush();
}
} catch (Exception e) {
System.out.println(e);
}
}
}
And from the client program the request made like this
private void btnSendActionPerformed(java.awt.event.ActionEvent evt) {
try {
String message = tfMessage.getText();
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out.println(message);
jtaLog.append( in .readLine() + "\n");
} catch (Exception e) {
System.out.println(e);
}
}

Multithreading with client server program

I am trying to implement multi threading with a client/server program I have been working on. I need to allow multiple clients to connect to the server at the same time. I currently have 4 classes: a Client, a Server, a Protocol and a Worker to handle the threads. The following code is what I have for those classes:
SocketServer Class:
public class SocketServer {
public static void main(String[] args) throws IOException {
int portNumber = 9987;
try (
ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
) {
Thread thread = new Thread(new ClientWorker(clientSocket));
thread.start(); //start thread
String inputLine, outputLine;
// Initiate conversation with client
Protocol prot = new Protocol();
outputLine = prot.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = prot.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("quit"))
break;
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
}
SocketClient Class:
public class SocketClient {
public static void main(String[] args) throws IOException
{
String hostName = "localhost";
int portNumber = 9987;
try (
Socket socket = new Socket(hostName, portNumber);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
) {
BufferedReader stdIn =
new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("quit"))
break;
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
} catch (UnknownHostException e) {
System.err.println("Don't know about host " + hostName);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to " +
hostName);
System.exit(1);
}
}
}
Protocol Class:
public class Protocol {
private static final int waiting = 0;
private static final int sentPrompt = 1;
private int status = waiting;
public String processInput(String theInput) {
String theOutput = null;
if (status == waiting) {
theOutput = "Please enter what you would like to retrieve: 'customer' or 'product' ";
status = sentPrompt;
}
else if ( status == sentPrompt ) {
if ( theInput.equalsIgnoreCase("product")) {
File f = new File("product.txt");
Scanner sc = null;
try {
sc = new Scanner(f);
} catch (FileNotFoundException ex) {
Logger.getLogger(Protocol.class.getName()).log(Level.SEVERE, null, ex);
}
while ( sc.hasNextLine() ) {
String line = sc.nextLine();
theOutput = "The current product entries are : " + line;
}
return theOutput;
}
else if ( theInput.equalsIgnoreCase("customer")) {
File f = new File("customer.txt");
Scanner sc = null;
try {
sc = new Scanner(f);
} catch (FileNotFoundException ex) {
Logger.getLogger(Protocol.class.getName()).log(Level.SEVERE, null, ex);
}
while ( sc.hasNextLine() ) {
String line = sc.nextLine();
theOutput = "The current customer entries are : " + line;
}
return theOutput;
}
else if ( theInput.equalsIgnoreCase("quit")) {
return "quit";
}
else {
return "quit";
}
}
return theOutput;
}
}
The ClientWorker Class:
public class ClientWorker implements Runnable {
private final Socket client;
public ClientWorker( Socket client ) {
this.client = client;
}
#Override
public void run() {
String line;
BufferedReader in = null;
PrintWriter out = null;
try {
System.out.println("Thread started with name:"+Thread.currentThread().getName());
in = new BufferedReader(new InputStreamReader(client.getInputStream()));
out = new PrintWriter(client.getOutputStream(), true);
} catch (IOException e) {
System.out.println("in or out failed");
System.exit(-1);
}
while (true) {
try {
System.out.println("Thread running with name:"+Thread.currentThread().getName());
line = in.readLine();
//Send data back to client
out.println(line);
//Append data to text area
} catch (IOException e) {
System.out.println("Read failed");
System.exit(-1);
}
}
}
}
When I run the server and client, everything works fine as expected. Then when I try to run another client, it just hangs there and does not prompt the client to give a response. Any insight into what I am missing is greatly appreciated!

Your server code should address implement below functionalities.
Keep accepting socket from ServerSocket in a while loop
Create new thread after accept() call by passing client socket i.e Socket
Do IO processing in client socket thread e.g ClientWorker in your case.
Have a look at this article
Your code should be
ServerSocket serverSocket = new ServerSocket(portNumber);
while(true){
try{
Socket clientSocket = serverSocket.accept();
Thread thread = new ClientWorker(clientSocket);
thread.start(); //start thread
}catch(Exception err){
err.printStackTrace();
}
}

How many times does serverSocket.accept() get called?
Once.
That's how many clients it will handle.
Subsequent clients trying to contact will not have anybody listening to receive them.
To handle more clients, you need to call serverSocket.accept() in a loop.

Production ready Socket server in Java

There are many tutorials where explains about socket server/client sides, but all them are very trivial. Is there any tutorial for production ready code? I'm new in sockets. There is a client, that sends strings to server. I must create the server side. in server side I read string from client and after some manipulation saves them in db. I must response to client only IF I get string like "Error" for example. and if there are no any daya from client in 30 secs, I must close client connection, but server side must works. this is my test Client side:
public class ClientSideSocket2 {
public static void main(String[] args) {
String serverName = "localhost";
int port = 5555;
String line = "";
Socket client = null;
try {
System.out.println("Connecting to " + serverName + " on port " + port);
client = new Socket(serverName, port);
System.out.println("Just connected to " + client.getRemoteSocketAddress());
PrintWriter toServer = new PrintWriter(client.getOutputStream(), true);
BufferedReader fromServer = new BufferedReader(new InputStreamReader(client.getInputStream()));
List<String> messages = new ArrayList<>();
for (int i = 0; i < 6; i++) {
messages.add("Message " + i+1);
}
messages.add("abc");
for (int i = 0; i < messages.size(); i++) {
toServer.println(messages.get(i));
if ((line = fromServer.readLine()) != null) {
System.out.println("Responce from server: " + line);
}
}
toServer.close();
fromServer.close();
} catch (IOException ex) {
ex.printStackTrace();
} finally {
try {
client.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
and my server side:
public class TRSServerInterface implements Runnable {
private ServerSocket serverSocket = null;
private Socket socket = null;
boolean runner = true;
String message = "";
public TRSServerInterface() {}
#Override
public void run() { // default run method of Thread class and Runnable interface
try {
int serverPort = 5555;
ServerSocket serverSocket = new ServerSocket(serverPort);
while(true) {
System.out.println("Waiting for connection...");
socket = serverSocket.accept();
System.out.println("Connected to " + socket.getRemoteSocketAddress());
//get the input and output streams
PrintWriter toClient = new PrintWriter(socket.getOutputStream(), true);
BufferedReader fromClient = new BufferedReader(new InputStreamReader(socket.getInputStream()));
do {
message = fromClient.readLine();
System.out.println("From client > " + message);
if (message.equals("abc")) {
toClient.println("Message from server");
}
else {
toClient.println("");
}
} while (!message.equals(""));
}
} catch (IOException ex) {
ex.printStackTrace();
} finally {
// try {
// objectOut.close();
// objectIn.close();
// socket.close();
// } catch (IOException e) {
// e.printStackTrace();
// }
}
}
}
is my solution corrent and how I can close connection with client if there are no any data in 30 secs.

There are several production ready frameworks that should be used instead of rolling your own. Socket timeouts can be used to control how long different operations are allowed to take before an exception is thrown.

Java, Sockets, BufferedReader and StringBuilder

Yestarday I wrote a post about Java and Sockets, and today I'm still here because I'm having an issue with BufferedReaders.
I searched some questions here in StackOverflow and I understand the problem, but I can't fix it
My "application" has got two parts: a server and a client, and the scope of the application is to execute MS-DOS commands on the machine where the server is running (the commands are sent by the client).
Now the code (I will post the total code because it's easier to understand, I will put a comment in non-working part of the code) Server:
import java.net.*;
import java.io.*;
public class TCPCmdServer {
public int port;
public ServerSocket server;
public final String version = "Beta 1.0";
TCPCmdServer(int port) {
this.port = port;
if (!createServer())
System.out.println("Cannot start the server");
else {
System.out.println("**********************************************");
System.out.println("Command executer, server version: " + version);
System.out.println("Server running on port " + port);
System.out.println("Code by luc99a alias L99");
System.out.println("**********************************************");
}
}
public boolean createServer() {
try {
server = new ServerSocket(port);
} catch (IOException e) {
e.printStackTrace();
return false;
}
return true;
}
public static void main(String[] args) {
TCPCmdServer tcp = new TCPCmdServer(5000);
while (true) {
Socket socket = null;
BufferedReader in = null;
BufferedWriter out = null;
try {
socket = tcp.server.accept();
System.out.println("A client has connected");
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
out.write("Welcome on the server... type the commands you like, type END to close the connection\n");
out.flush();
} catch (IOException exc) {
exc.printStackTrace();
}
if (socket != null && in != null && out != null) {
try {
String cmd = null;
while (!(cmd = in.readLine()).equals("END")) {
System.out.println("Recieved: " + cmd);
Process p = Runtime.getRuntime().exec(cmd);
BufferedReader pRead = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line;
StringBuilder builder = new StringBuilder();
while ((line = pRead.readLine()) != null) {
builder = builder.append(line + "\n");
}
out.write(builder.toString() + "\n");
//here is sent "EnD"
out.write("EnD \n");
out.flush();
System.out.println(builder.toString());
pRead.close();
}
} catch (IOException ex) {
ex.printStackTrace();
} finally {
System.out.println("Closing connection...");
try {
socket.close();
in.close();
out.close();
} catch (IOException excp) {
excp.printStackTrace();
}
}
}
}
}
}
And now the code for the client part
import java.net.*;
import java.io.*;
public class TCPCmdClient {
public Socket socket;
public int port;
public String ip;
public final String version = "Beta 1.0";
TCPCmdClient(String ip, int port) {
this.ip = ip;
this.port = port;
if (!createSocket())
System.out.println("Cannot connect to the server. IP: " + ip + " PORT: " + port);
else {
System.out.println("**********************************************");
System.out.println("Command executer, client version: " + version);
System.out.println("Connected to " + ip + ":" + port);
System.out.println("Code by luc99a alias L99");
System.out.println("**********************************************");
}
}
public boolean createSocket() {
try {
socket = new Socket(ip, port);
} catch (IOException e) {
return false;
}
return true;
}
public static void main(String[] args) {
TCPCmdClient client = new TCPCmdClient("127.0.0.1", 5000);
try {
BufferedReader sysRead = new BufferedReader(new InputStreamReader(System.in));
BufferedReader in = new BufferedReader(new InputStreamReader(client.socket.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(client.socket.getOutputStream()));
String response = in.readLine();
System.out.println("Server: " + response);
boolean flag = true;
while (flag) {
System.out.println("Type a command... type END to close the connection");
String cmd = sysRead.readLine();
out.write(cmd + "\n");
out.flush();
if (cmd.equals("END")) {
client.socket.close();
sysRead.close();
in.close();
out.close();
flag = false;
} else {
//The loop doesn't finish because the reader
//listens for a new line
//so I used the string "EnD", sent by the server to
//stop the loop, anyway it doesn't seem to work
//I put a comment in the server where "EnD" is sent
String output;
while (((output = in.readLine()) != null)) {
if (output.equals("EnD")) {
break;
} else {
System.out.println(output);
}
}
System.out.println(" *************************************** ");
}
}
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
The problem is that the BufferedReader waits for a new line forever in the while loop (I wrote a comment in the code). I tryed to stop it using a "special string", but it doesn't seem to work.
I can't change the while in
String output;
while (((output = in.readLine()) != null) && output.length > 0)
{
//code here...
}
because in the output of the MS-DOS command (think on "ipconfig") are also present empty lines.
How could I correct it?
Thank you for your help!

your client Sends "EnD " (with a whitespace at the end) and you are comparing to "EnD" without a whitespace. So the two strings are not equal. try to send it without the white space:
out.write("EnD\n");

Space is missing. In TCPCmdClient.java change
if (output.equals("EnD")) {
to
if (output.equals("EnD ")) {

Android TCP Client/Server not passing messages properly (Only first received)

I have created two android applications, a client and a server, utilizing TCP to communicate across devices. On the server, I have this code to listen for TCP communication:
private class StartServer implements Runnable {
public void run() {
getState(); // This just refreshes the server state
try {
serverSocket = new ServerSocket(5000);
appendLog("Server successfully listening ["+getLocalIpAddress() + ":5000]"); //appendLog function just uses runOnUiThread() to update the log textview
} catch (IOException e) {
appendLog("Could not listen on port: 5000");
//System.exit(-1);
}
BufferedReader in = null;
BufferedWriter out = null;
String input = null;
try {
clientSocket = serverSocket.accept();
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
out = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
while (serverState) { //variable set by our getState() function
input = in.readLine();
appendLog("Received: " + input);
this.gotMessage(out, input);
}
in.close();
out.close();
} catch (IOException e) {
//appendLog(e.toString());
appendLog("Accept failed: 5000");
//System.exit(-1);
}
}
Which calls this function to actually parse the recieved messages:
private void gotMessage(BufferedWriter output, String msg) {
if (msg != null) {
String sString = msg;
int to_do = 0;
if (msg.matches("^(?i)(exit|quit|close)$")) {
appendLog("Exiting");
sString = "Goodbye";
to_do=1;
} else if (msg.matches("^(?i)(launch|run|open)\\s(.+)")) {
appendLog("Launching application");
sString = "Launching application";
} else if (msg.matches("^(?i)(turn off|server off|deactivate)$")) {
appendLog("Turning off server due to remote command.");
sString = "Turning off...";
to_do=2;
} else if (msg.matches("^(?i)(restart|reboot)$")) {
appendLog("Resetting server");
sString = "Rebooting now...";
to_do=3;
}
try {
output.write("S: " + sString);
output.newLine();
output.flush();
} catch (IOException e) {
appendLog("Cannot parse message");
}
switch(to_do) {
case 0:
break;
case 1:
System.exit(0);
break;
case 2:
serverOff();
break;
case 3:
serverOff();
serverOn();
break;
default:
break;
}
}
}
}
The thread itself for the server is started using Thread t = new Thread(new StartServer()); t.start(). And to the best of my knowledge, this works fine. I can open up a terminal and telnet to the IP and port, and pass communication back and forth without error. But when I try to do the same from the client code below. I only get the first message, and anything else I pass in just dissappears into the void.
public void sendToServer(View v) {
try {
String ip = ((TextView)findViewById(R.id.ip_box)).getText().toString(); //User entered IP address
String to_send = ((EditText)findViewById(R.id.send_to_server)).getText().toString(); //User entered text to send
this.s = new Socket(ip, 5000);
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
appendLog("Sending: " + to_send);
out.write(to_send);
out.newLine();
out.close();
} catch (Exception e) {
Log.d("error", e.toString());
}
}

Do you have line-end character in your to_send string? if no, just add out.newLine() to your client code:
appendLog("Sending: " + to_send);
out.write(to_send);
out.newLine();
You server code should look like this to support multiple clients:
// main server loop
while (serverIsActive) {
clientSocket = serverSocket.accept();
// spawn new thread for each client
ClientThread ct = new ClientThread(clientSocket);
ct.start();
}
ClientThread should work with client socket and have its own loop for reading lines. It should stop as soon as client closes socket:
class ClientThread {
...
public void run() {
....
while ((inputLine = in.readLine()) != null) {
// process client message
}
in.close();
}
}