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create a java server socket that waits for messages from client using Thread Pool

#FXML
private TextArea textarea;
#FXML
private ImageView imagev;
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
Serverth Server = new Serverth();
Server.start();
}
class Serverth extends Thread {
#Override
public void run() {
try {
final int NUM_THREAD = 99;
ServerSocket socket = new ServerSocket(8078);
ExecutorService exec = Executors.newFixedThreadPool(NUM_THREAD);
System.out.println("SERVER SOCKET CREATED");
while (!isInterrupted()) {
Socket in = socket.accept();
Runnable r = new ThreadedHandler(in);
exec.execute(r);
}
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
}
class ThreadedHandler implements Runnable {
private Socket incoming;
public ThreadedHandler(Socket in) {
incoming = in;
}
public void run() {
try {
try {
ObjectInputStream is=new ObjectInputStream(incoming.getInputStream());
while(true) {
if (is.available() > 0) {
String line = is.readUTF();
textarea.appendText("\n" + "[" + new java.util.Date() + "] : " + line);
if (line.contains("inviato")) {
Object obj = is.readObject();
Email ema = (Email) obj;
try {
SimpleDateFormat formatter = new SimpleDateFormat("dd-M-yyyy-hh-mm-ss");
FileOutputStream fileOut = new FileOutputStream("src/Server/" + ((Email) obj).getDestinat() + "/" + formatter.format(((Email) obj).getData()) + ".txt");
ObjectOutputStream objectOut = new ObjectOutputStream(fileOut);
objectOut.writeObject(ema);
objectOut.flush();
objectOut.close();
System.out.println("The Object was succesfully written to a file");
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
}
} catch(IOException ex) {
ex.printStackTrace();
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
try {
incoming.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}
Inside the run method (in Serveth class), I create a server socket and call exec.execute method.
Inside the run method (in ThreadedHandler class), the server is waiting for messages from the client (in this specific case, it creates a new .txt file but it is not important).
Everything works but causes excessive use of the CPU and lag!!!

InputSteam.available method returns a value instantly, telling you no bytes are available to be read, so this code runs a very "hot" spin loop:
while(true) {
if (is.available() > 0) {
...
}
}
The available method is rarely useful and often gives confusing results (see for example inputstream.available() is 0 always). I would suggest you get rid of the if statement altogether:
while(true) {
String line = is.readUTF();
textarea.appendText("\n" + "[" + new java.util.Date() + "] : " + line);
...
}
There's no way for this your code to exit the loop normally. You may want to add a mechanism for the client to disconnect from the server.

Sending a json object with jetty in java

I can't figure out why nothing happens.
I'm trying to write a java program that sends a json object to a jetty server.
The server is already written(by someone else,its an project) and only excepts certain json objects. But he doesn't get anything from my program.
public class client {
final static String HOST = "localhost";
final static int PORT = 3000;
public static void main(String[] args)
{
String URIString = "ws://" + HOST + ":" + PORT + "/servlets";
URI uri = URI.create(URIString);
WebSocketClient client = new WebSocketClient();
JSONObject js = new JSONObject();
js.put("toke","hallo");
Clientsocket clientsocket = new Clientsocket();
try {
client.start();
Future<Session> fut = client.connect(clientsocket, uri);
clientsocket.getSession().getRemote().sendString(js.toJSONString());;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
public class Clientsocket extends WebSocketAdapter {
//private static final Logger LOG = Log.getLogger(Clientsocket.class);
#Override
public void onWebSocketClose(int statusCode,String reason)
{
super.onWebSocketClose(statusCode, reason);
//LOG.info("Websocket Close:{} - {} ", statusCode,reason);
}
#Override
public void onWebSocketConnect(Session session)
{
super.onWebSocketConnect(session);
//LOG.info("Websocket Connect: {}", session);
}
}
error message when started:
2018-06-22 14:26:43.789:INFO::main: Logging initialized #257ms to org.eclipse.jetty.util.log.StdErrLog
java.lang.NullPointerException
[both classes: clientsocket, client][1]

I think you didn't wait for the connect to complete.
Future<Session> fut = client.connect(clientsocket, uri);
Session session = fut.get(); // wait for connect to complete (or throw exception)
session.getRemote().sendString(js.toJSONString());

Handling multi Java TCP clients with Threads

I have been working with TCP server/client stuff for a while. I am actully good at UDP programming when it comes to connecting more than one user that is multiple clients. I tried to do the same on a TCP server that i made using Threads but whenever the Thread gets to this piece of code
String reader = (String)in.readObject();
an error is generated and the thread stops executing the code but the thread still runs the program keeping it alive.
Anyway here is the entire source code :
public class TestServer implements Runnable {
private Thread run, streams, connect, receive, send;
private ServerSocket socket;
private Socket conn;
private ObjectInputStream in;
private ObjectOutputStream out;
private boolean running, incomingMessage = false;
private int port;
public TestServer(int port) throws IOException {
this.port = port;
socket = new ServerSocket(port);
console("Server stated on : " + InetAddress.getLocalHost() + " : " + port);
run = new Thread(this, "Run");
run.start();
}
public void run() {
running = true;
connect();
receive();
}
private void connect() {
connect = new Thread("Connect") {
public void run() {
while(running) {
try {
conn = socket.accept();
} catch (IOException e) {
e.printStackTrace();
}
console("You are now connected" + conn.getInetAddress().toString() + " : " + conn.getPort());
try {
setupStreams();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}; connect.start();
}
private void setupStreams() throws IOException {
streams = new Thread("Streams") {
public void run() {
try {
console("Setting up Streams");
out = new ObjectOutputStream(conn.getOutputStream());
out.flush();
in = new ObjectInputStream(conn.getInputStream());
console("Streams are now setup");
incomingMessage = true;
receive.start();
} catch(IOException e) {
e.printStackTrace();
}
}
}; streams.start();
}
private void receive() {
receive = new Thread("Receive") {
public void run() {
while(incomingMessage) {
String message = "";
try {
message = (String) in.readObject();
//This is the only flaw the program
} catch (ClassNotFoundException | IOException e) {
e.printStackTrace();
}
console("Client : " + message);
}
}
};
}
private void console(String message) {
System.out.println(message);
}
public static void main(String[] args) {
try {
new TestServer(1234);
} catch (IOException e) {
e.printStackTrace();
}
}
}
FYI am not new to this. The error is caused because the server starts receiving packets even when there are no packets to be received. But because the thread forces it to receive it, i generates the error in the thread and dont know any other way to counter this. So please help. Thanks in Advance.

You shouldn't need 2 threads per connection. One thread is all that's required. After the connection is accepted, pass it to a worker thread to start reading. This can be done in a while loop in the worker thread.
Even though the socket's input stream can be read, the ObjectInputStream() class is more sensitive. If there is any error, its state is corrupted and it can't be used.
while (true) {
try {
Object input = in.readObject();
message = (String) input;
} catch (IOException e) {
e.printStackTrace();
break; //unrecoverable
} catch (ClassNotFoundException e) {
e.printStackTrace();
break; //unrecoverable
}
console("Client : " + message);
}
It's a better design to use a specific message protocol instead of sending serialized Java objects. For example if you are sending Strings like your sample, an InputStreamReader can be used to convert bytes to characters more easily and with less error handling.
These resources would be helpful to you:
https://docs.oracle.com/javase/tutorial/networking/sockets/clientServer.html#later
Java - Listening to a socket with ObjectInputStream
ObjectInputStream(socket.getInputStream()); does not work

Server Client multithread

I'm doing my assignment with Chat Server-client. Here is how i start server
public static void StartServer(){
// Create socket
try {
serversocket = new ServerSocket(ServerPort);
} catch (Exception e) {
isError = true;
ERRORCODE = "ERROR! Cannot create a new socket! " + e.getMessage();
return;
}
// A new thread to wait for connection
Thread TH_Wait4Connection = new Thread(){
public void run(){
while(true){
String ERRORHere = "-1"; // To specify whre the Errors are
try {
Connection = new Socket();
Connection = serversocket.accept();
} catch (Exception e) {
ERRORCODE = ERRORHere + " : " + e.getMessage();
return;
}
// Another Thread to handle a connection
try {
ERRORHere = "1";
Thread Client = new Thread(new ConnHandler(Connection));
ERRORHere = "2";
threadList.add(Client);
ERRORHere = "3";
Client.start();
ERRORHere = "4";
} catch (Exception e) {
ERRORCODE = ERRORHere + " : " + e.getMessage();
return;
}
try {Thread.sleep(10);} catch (Exception e) {}
} // End why loop
} // End run()
};
TH_Wait4Connection.start();
}
When i debug in eclipse, my clients can connect to server and everything is fine, server creates threads and no exception catched. But if i Run, it goes into the last catch and my ERRORCODE
ERRORCODE = ERRORHere + " : " + e.getMessage();
is
1 : 6 > 4
What are those errors? And how to fix it?
Thank for read.
Update class ConnHandler
public class ConnHandler implements Runnable{
public ConnHandler(Socket Connection) throws Exception{
InputStream IS = Connection.getInputStream();
byte[] InData = new byte[1024];
int bytesCount = IS.read(InData);
// Remove first 6 bytes
byte[] NewInData = Arrays.copyOfRange(InData, 6, bytesCount);
}
public void run(){}
}

Your problem is this line in ConnHandler:
byte[] NewInData = Arrays.copyOfRange(InData, 6, bytesCount);
When calling this line bytesCount is 4. Since argument FROM is bigger then argument TO (6 > 4), it throws an IllegalArgumentException. See here for more information about this method.
In general it is not advisable to catch the type Exception instead of the subtypes in different catch-blocks. Your current implementation could hide unchecked Exceptions. Further if you catch the subtypes, you will know what type occurred (without manually checking) and debug faster, like in your current case.

send a file to a client after long wait

i've a java servlet that makes some reports. When a user choose a report it makes a query on a db and stream the xls report to the client. All in synchronous way. The problem is that sometimes i've a lot of records to fetch from the db and i would like to give a better user experience, allowing the user to do something else while the report is processing and popping out in some way the link when the process is finished. Is there a java library or some techniques to avoid the long waiting and achieve that goal?
Right now i've prepared a piece of code that in a asynchronous way completes the report and sends an email to the registered client, with the url from wich download the file, but it has to be replaced with something else because i can no longer communicate by email.
Thanks in advance

heres my take on this, i dont know of a single library that will exactly match you needs, youd probably need some custom development here.
I believe you have implemented async service that on completion sends
out an email for notification. Instead of sending out an email, let
that thread update a job table of some sort -- an entry in a db table
or some application/session scoped map.
Have a servlet/restful ws
expose that job table at some url. Poll the url at regular
intervals. Ajax poll is a standard feature in js libraries JQuery,
Prototype.
When you get a response that some report is complete, show
some popup or may be a facebook you-have-notification kind of thing
on the client side.
i have not considered authentication/authorization issues here, you need to take care of that as well.
Hope this helps

A multithreaded client server program to download my image files.
Since there are four files to download the client makes 4 connection attempts. This is not limited to 4 but the files sent by the FileServer will get repeated after the fourth attempt. The save dialog and file saving is done in different threads so as to not hamper the file downloading.
Here is the FileServer...
public class FileServer {
private final ExecutorService exec = Executors.newCachedThreadPool();
final String[] fileNames = {
"C:\\Users\\clobo\\Pictures\\Arpeggios\\Ex 1.jpg",
"C:\\Users\\clobo\\Pictures\\Arpeggios\\Ex 2.jpg",
"C:\\Users\\clobo\\Pictures\\Arpeggios\\Ex 3.jpg",
"C:\\Users\\clobo\\Pictures\\Arpeggios\\Ex 4.jpg"
};
public void start() throws IOException {
ServerSocket socket = new ServerSocket(7777);
System.out.println("Waiting for client message...");
while (!exec.isShutdown()) {
try {
for (final String fileName : fileNames){
final Socket conn = socket.accept();
exec.execute(new Runnable() {
public void run() {
sendFile(conn,fileName);
}
});
}
} catch (RejectedExecutionException e) {
if (!exec.isShutdown())
log("task submission rejected", e);
}
}
}
public void stop() {
System.out.println("Shutting down server...");
exec.shutdown();
}
private void log(String msg, Exception e) {
Logger.getAnonymousLogger().log(Level.WARNING, msg, e);
}
public void sendFile(Socket conn, String fileName) {
File myFile = new File(fileName);
if (!myFile.exists()) {
log("File does not exist!",null);
}
// file does exist
System.out.println(Thread.currentThread().getName());
System.out.println("AbsolutePath:" + myFile.getAbsolutePath());
System.out.println("length: " + myFile.length());
if (myFile.exists()) {
try {
ObjectOutputStream oos = new ObjectOutputStream(
conn.getOutputStream());
oos.writeObject(myFile);
oos.close();
} catch (IOException e) {
log("IOException Error", e);
e.printStackTrace();
}
}
}
public static void main(String[] args) throws IOException {
FileServer fs = new FileServer();
fs.start();
}
}
here is the FileServerClient...
public class FileServerClient {
private final ExecutorService exec = Executors.newCachedThreadPool();
Frame myFrame = new Frame();
List<File> fileList = new ArrayList<File>();
public void receiveFileFromServer() throws Exception{
Socket sock = null;
InputStream socketInputStream = null;
String host = "localhost";
int port = 7777;
for (int i=0;i<4;i++) {
sock = new Socket(host, port);
socketInputStream = sock.getInputStream();
System.out.println("Connection successful...");
// recieve the file
ObjectInputStream ois = new ObjectInputStream(socketInputStream);
// file from server is deserialized
final File myfile = (File) ois.readObject();
fileList.add(myfile);
// deserialized file properties
System.out.println("AbsolutePath: " + myfile.getAbsolutePath());
System.out.println("FileName:" + myfile.getName());
System.out.println("length" + myfile.length());
exec.execute(new Runnable() {
public void run() {
saveFile(myfile);
}
});
}
}
private void saveFile(File myfile) {
FileDialog fileDialog = new FileDialog(myFrame,
"Choose Destination for "+ myfile.getName(), FileDialog.SAVE);
fileDialog.setDirectory(null);
fileDialog.setFile("enter file name here");
fileDialog.setVisible(true);
String targetFileName = fileDialog.getDirectory()
+ fileDialog.getFile() + ".jpg";
System.out.println("File will be saved to: " + targetFileName);
copyBytes(myfile, targetFileName);
}
private void copyBytes(File originalFile, String targetFileName) {
try {
FileInputStream in = new FileInputStream(originalFile);
FileOutputStream out = new FileOutputStream(targetFileName);
int c;
while ((c = in.read()) != -1) {
out.write(c);
}
out.close();
in.close();
} catch (Exception e) {
log("IOException Error", e);
}
}
private void log(String msg, Exception e) {
Logger.getAnonymousLogger().log(Level.WARNING, msg, e);
}
public static void main(String[] args) throws Exception {
FileServerClient client = new FileServerClient();
client.receiveFileFromServer();
}
}

You could make an asynchronous request from the client. Lets assume that you client is an html page. When the user selects a report and clicks on 'submit' you could fire an ajax request with the report parameters (jquery can be useful for this). It would be good to keep a section on the user homepage that says something like 'prepared reports'. The client can then goto the prepared report section to download the report. As specified in the comments above, you may also have to implement a popup that informs the user that the requested report is ready. the popup is shown when the ajax requests returns successfully. However, the client may have logged out by the time the report finishes, so it may be a good idea to make the download link available again in the 'prepared reports' section when the user logs in.