Let's say I got System.in
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
result = br.readLine();
while (!result.isEmpty()) {
if (result.equalsIgnoreCase("exit")) {
userStr="exit";
System.exit(0);
} else if (result.equalsIgnoreCase("list")) {
userStr="list";
} else if (result.equalsIgnoreCase("kill")) {
userStr="kill";
} else if (result.equalsIgnoreCase("help")) {
userStr="help";
}
and
ServerSocket socketListener = new ServerSocket(port);
while (true) {
Socket client = socketListener.accept();
new ServerThread(client,userStr); //pass userStr to Thread
}
i don't understand how can i "wait for console commands" and pass them to active Thread. I need to accept() clients, pass them to thread. If I entered a command into the server console like for example; "kill Username"(disconnect user) or "list"(list of Usernames)
my server should pass commands to threads.
p/s I need manage server, manage implemented by entering the console commands.
As easy solution you can block you thread untill it will recieve a task to execute :
class Task implements Runnable {
AtomicReference<String> atomicReference = new AtomicReference<String>(null);
#Override
public void run() {
while (true) {
String command = atomicReference.getAndSet(null);
if (command != null) {
//do staff with command
}
}
}
public void executeCommand(String command) {
atomicReference.set(command);
}
}
Use it like this:
ServerSocket socketListener = new ServerSocket(port);
Task task = new Task();
new Thread(task).start();
while (true) {
Socket client = socketListener.accept();
task.executeCommand(userCommand);
}
But if you need more complex solution I can advice you to read about Java Concurrency package:
Avesome book about that
Good article
Related
I am writing a Java client/server GUI application using sockets and here is the problem:
I have a button to start listening for a specified port:
button actionPerformed method
private void listenButtonActionPerformed(java.awt.event.ActionEvent evt) {
int port = Integer.parseInt(portTextfield.getText(), 10);
try {
socket.listen(port);
} catch (IOException ex) {
}
}
Here is the socket.listen method
public static void listen() throws IOException {
ServerSocket ss = new ServerSocket(port);
while (true)
new socket(ss.accept());
}
"socket" class extends "Thread"
So after ss.accept() returns a value it creates new socket instance in separate thread.
After clicking the button the GUI freezes because inside the socket.listen method there is an infinite loop. How can I avoid that?
You have two pitfalls in your design:
ss.accept() is a blocking call so your UI will freeze until there is an incoming connection
Never run while(true) loops in the EDT.
Instead do the following:
When the button is clicked create a thread that will start listening for incoming connections.
Whenever you have an incoming connection, create another thread that will take the incoming client connection and deal with it.
as long as your
new socket(ss.accept());
returns immediately, you only need to change your
while (true)
this puts the EDT (Event Dispatch Thread) into an infinite loop and your GUI becomes irresponsive. So, delete this line.
If you can't then use the SwingWorker class ( http://docs.oracle.com/javase/7/docs/api/javax/swing/SwingWorker.html#process(java.util.List)
Create a nested class that extents SwingWorker. Just call a swingWoker.execute(); (after you have created its object) in your listenButtonActionPerformed(java.awt.event.ActionEvent evt) method.
See the tutorial: http://docs.oracle.com/javase/tutorial/uiswing/concurrency/worker.html
Never create a new thread and run it from from the Swing EDT
Check this out: http://javarevisited.blogspot.ro/2012/02/what-is-blocking-methods-in-java-and.html
1) If you are writing GUI application may be in Swing never call
blocking method in Event dispatcher thread or in the event handler.
for example if you are reading a file or opening a network connection
when a button is clicked don't do that on actionPerformed() method,
instead just create another worker thread to do that job and return
from actionPerformed(). this will keep your GUI responsive, but again
it depends upon design if the operation is something which requires
user to wait than consider using invokeAndWait() for synchronous
update.
Using multiple threads: http://javarevisited.blogspot.ro/2011/02/how-to-implement-thread-in-java.html
You will need to use Multi-Threading. If I where you, I would separate the GUI code and the server code and when the button is pressed, I simply launch the Server code as a new Thread.
Your code is freezing the GUI basically because all events are executed on the Event Dispatcher Thread (EDT) which is the thread which takes care of all your GUI stuff and respective events. If you either block it, stop it or throw in loops it will affect on its performance.
Try these...
1. During getting the initial connection delay can occur, so first create and empty socket,then try to connect to the server.
`Socket s = new Socket();`
`s.connect(new InetSocketAddress("ip_addr",port_nos),1000);`
2. And Secondly always keep the Non-UI work out of Your UI thread..
Here is my Example of Server - Client Communication..
Client side code:
public class ClientWala {
public static void main(String[] args) throws Exception{
Boolean b = true;
Socket s = new Socket();
s.connect(new InetSocketAddress("127.0.0.1", 4444),1000);
System.out.println("connected: "+s.isConnected());
OutputStream output = s.getOutputStream();
PrintWriter pw = new PrintWriter(output,true);
// to write data to server
while(b){
if (!b){
System.exit(0);
}
else {
pw.write(new Scanner(System.in).nextLine());
}
}
// to read data from server
InputStream input = s.getInputStream();
InputStreamReader isr = new InputStreamReader(input);
BufferedReader br = new BufferedReader(isr);
String data = null;
while ((data = br.readLine())!=null){
// Print it using sysout, or do whatever you want with the incoming data from server
}
}
}
Server side code:
import java.io.*
import java.net.*;
public class ServerTest {
ServerSocket s;
public void go() {
try {
s = new ServerSocket(44457);
while (true) {
Socket incoming = s.accept();
Thread t = new Thread(new MyCon(incoming));
t.start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
class MyCon implements Runnable {
Socket incoming;
public MyCon(Socket incoming) {
this.incoming = incoming;
}
#Override
public void run() {
try {
PrintWriter pw = new PrintWriter(incoming.getOutputStream(),
true);
InputStreamReader isr = new InputStreamReader(
incoming.getInputStream());
BufferedReader br = new BufferedReader(isr);
String inp = null;
boolean isDone = true;
System.out.println("TYPE : BYE");
System.out.println();
while (isDone && ((inp = br.readLine()) != null)) {
System.out.println(inp);
if (inp.trim().equals("BYE")) {
System.out
.println("THANKS FOR CONNECTING...Bye for now");
isDone = false;
s.close();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
try {
s.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
e.printStackTrace();
}
}
}
public static void main(String[] args) {
new ServerTest().go();
}
}
I am writing a Java client application(Basic Java Net package with TCP/IP). The client must take input from the system.in and at the same time must listen to any messages coming from server through socket inputstream.
Once an input from the system.in is received, the client will get that input, do some processing and send it to the server as a request.
So basically 2 processes run,
-listening to client request
-listning to server responses.
I implemented 2 threads for this and ran the processing of messages in the main thread.
Is this good enough design.?
And is there a way to return the message received from the system.in to the main thread. The threads run() method returns void. I used a volatile variable to return the string received but its said that volatile is very costly since it doesn't use cpu cache to store the variable.
You can review these two projects I've written for an example of java sockets and multithreading.
Client
Server
I guess the ClientExample is the one you are searcing for but you can take a look at the server part too.
Basically the idea is to start two separate threads that listen for the different inputs - socket and console.
final Thread outThread = new Thread() {
#Override
public void run() {
System.out.println("Started...");
PrintWriter out = null;
Scanner sysIn = new Scanner(System.in);
try {
out = new PrintWriter(socket.getOutputStream());
out.println(name);
out.flush();
while (sysIn.hasNext() && !isFinished.get()) {
String line = sysIn.nextLine();
if ("exit".equals(line)) {
synchronized (isFinished) {
isFinished.set(true);
}
}
out.println(line);
out.flush();
disconnect();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (out != null) {
out.close();
}
}
};
};
outThread.start();
and another thread for the socket input:
final Thread inThread = new Thread() {
#Override
public void run() {
// Use a Scanner to read from the remote server
Scanner in = null;
try {
in = new Scanner(socket.getInputStream());
String line = in.nextLine();
while (!isFinished.get()) {
System.out.println(line);
line = in.nextLine();
}
} catch (Exception e) {
// e.printStackTrace();
} finally {
if (in != null) {
in.close();
}
}
};
};
inThread.start();
I hope this will help you :)
I'm using a server socket to accept clients on the main thread, when a thread is accepted,the clients socket is given to a handler which is started in a new thread to process communications. However, before I start running my server to access clients, it connects to a second server which it must list to and be able to respond to and pass on the messages it gets to it's clients.
Hopefully this image illustrate what I mean:
The small server must be continuously listening for input from the big server, and also able to output responses.
//Default constructor
private smallServer(){}
//method to initialise and start the server
public static void StartServer(int port) throws IOException {
smallServer ss = new smallServer();
ss.bs= new bigServerClient(ss);
Thread nsc_Thread = new Thread(ss.bsc);
bsc_Thread.start();
//accepts clients and starts new thread for them
ss.ServerRun(port);
}
private void ServerRun(int port) throws IOException {
ServerSocket server = new ServerSocket(port);
server.setSoTimeout(50);
while (run) {
Socket client = null;
try {
client = server.accept();
} catch (SocketTimeoutException e) {
}
if (client != null) {
ClientHandler handler = new ClientHandler(client, this);
Thread handleThread = new Thread(handler);
handleThread.start();
}
}
if (!run) {
synchronized (ClientHandler.handlers) {
for (ClientHandler handler : ClientHandler.handlers) {
handler.terminateHandler();
}
}
System.exit(0);
}
}
public void processBigServerCommand(String toProcess) {
System.out.println("RESEAVED: " + toProcess);
}
The big server client(on the small server) then does this:
public class bigServerClient implements Runnable {
private smalsServer ss;
private PrintWriter printer;
private BufferedReader reader;
private Socket socket;
public bigServerClient(smallServer _ss) throws IOException {
ss = _ss;
socket = new Socket("Localhost", 5000);
printer = new PrintWriter(socket.getOutputStream());
reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
printer.flush();
SendBigServerMessage("Starting String");
}
private void SendBigServerMessage(String toSend) {
printer.print(toSend);
printer.flush();
}
#Override
public void run() {
try {
while (ss.state()) {
String inputLine;
while ((inputLine = reader.readLine()) != null) {
ss.processBigServerCommand(inputLine);
System.out.println(inputLine);
}
}
} catch (IOException e) {
} finally {
try {
socket.close();
} catch (IOException ex) {
}
}
}
}
From what's above, can anyone see why the big server client isn't responding to the big server when a message is sent? I'm guessing it's something to do with the main thread blocking the second thread, but I'm not sure... Any help would be greatly appreciated.
You lost me in your code...
Simplify it.
Your smallServer (see class names conventions) should have persistent connection to BigServer (effectively it is BigServer client) - you can implement it in your smallServer class, it should connect (once) and open I/O to BigServer (once) and close everything once the connection is terminated.
As your smallServer will handle multiple clients and pass their requests to BigServer there is no guarantee of the order of BigServer responses - you should do something to handle that (maybe pass UUID with requests?)
Simplify your smallServer and make sure that it runs...
I'm trying to make a networking application, for a proof of concept project.
I need to keep the connection open, the joined clients, but the while loop I'm running never gets out of the first loop.
Code:
public class comm implements Runnable {
private Socket socket;
private String line, input;
boolean sending = true;
boolean connected = false;
private int me;
private BufferedReader br;
private PrintWriter pw;
doComms(Socket server) {
socket = server;
me = Main.connected;
}
public void run() {
try {
br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
pw = new PrintWriter(socket.getOutputStream(), true);
while (true) {
System.out.println("Waiting");
readCommand();
}
} catch (Exception ex) {
System.out.println(ex);
}
}
private void readCommand() throws Exception {
String str;
while (br.readLine() != null) {
if (!connected) {
pw.println("connect");
}
str = br.readLine();
System.out.println(str);
if (str.startsWith("!START!")) {
System.out.println("User connected");
connected = true;
String[] split = str.split("#");
Main.jTable1.getModel().setValueAt(split[1], me, 2);
Main.jTable1.getModel().setValueAt(split[2], me, 3);
Main.jTable1.getModel().setValueAt("Connected...", me, 4);
}
}
}
}
Starting that code is fine, all it does is makes a new thread for each connected users, and the client software runs fine too. what am I doing wrong?
My best guess. It never gets out of the first readCommand call because readCommand itself is in an infinite loop:
while (br.readLine() != null) {
br.readLine will block until the next line from the socket input arrives. So the only way for the loop to exit is for the remote client to disconnect.
But the while loop I'm running never gets out of the first loop.
The first loop you are referring to is:
while(true) { ... }
This will never exit because true is always true.
I am writing a Java client/server GUI application using sockets and here is the problem:
I have a button to start listening for a specified port:
button actionPerformed method
private void listenButtonActionPerformed(java.awt.event.ActionEvent evt) {
int port = Integer.parseInt(portTextfield.getText(), 10);
try {
socket.listen(port);
} catch (IOException ex) {
}
}
Here is the socket.listen method
public static void listen() throws IOException {
ServerSocket ss = new ServerSocket(port);
while (true)
new socket(ss.accept());
}
"socket" class extends "Thread"
So after ss.accept() returns a value it creates new socket instance in separate thread.
After clicking the button the GUI freezes because inside the socket.listen method there is an infinite loop. How can I avoid that?
You have two pitfalls in your design:
ss.accept() is a blocking call so your UI will freeze until there is an incoming connection
Never run while(true) loops in the EDT.
Instead do the following:
When the button is clicked create a thread that will start listening for incoming connections.
Whenever you have an incoming connection, create another thread that will take the incoming client connection and deal with it.
as long as your
new socket(ss.accept());
returns immediately, you only need to change your
while (true)
this puts the EDT (Event Dispatch Thread) into an infinite loop and your GUI becomes irresponsive. So, delete this line.
If you can't then use the SwingWorker class ( http://docs.oracle.com/javase/7/docs/api/javax/swing/SwingWorker.html#process(java.util.List)
Create a nested class that extents SwingWorker. Just call a swingWoker.execute(); (after you have created its object) in your listenButtonActionPerformed(java.awt.event.ActionEvent evt) method.
See the tutorial: http://docs.oracle.com/javase/tutorial/uiswing/concurrency/worker.html
Never create a new thread and run it from from the Swing EDT
Check this out: http://javarevisited.blogspot.ro/2012/02/what-is-blocking-methods-in-java-and.html
1) If you are writing GUI application may be in Swing never call
blocking method in Event dispatcher thread or in the event handler.
for example if you are reading a file or opening a network connection
when a button is clicked don't do that on actionPerformed() method,
instead just create another worker thread to do that job and return
from actionPerformed(). this will keep your GUI responsive, but again
it depends upon design if the operation is something which requires
user to wait than consider using invokeAndWait() for synchronous
update.
Using multiple threads: http://javarevisited.blogspot.ro/2011/02/how-to-implement-thread-in-java.html
You will need to use Multi-Threading. If I where you, I would separate the GUI code and the server code and when the button is pressed, I simply launch the Server code as a new Thread.
Your code is freezing the GUI basically because all events are executed on the Event Dispatcher Thread (EDT) which is the thread which takes care of all your GUI stuff and respective events. If you either block it, stop it or throw in loops it will affect on its performance.
Try these...
1. During getting the initial connection delay can occur, so first create and empty socket,then try to connect to the server.
`Socket s = new Socket();`
`s.connect(new InetSocketAddress("ip_addr",port_nos),1000);`
2. And Secondly always keep the Non-UI work out of Your UI thread..
Here is my Example of Server - Client Communication..
Client side code:
public class ClientWala {
public static void main(String[] args) throws Exception{
Boolean b = true;
Socket s = new Socket();
s.connect(new InetSocketAddress("127.0.0.1", 4444),1000);
System.out.println("connected: "+s.isConnected());
OutputStream output = s.getOutputStream();
PrintWriter pw = new PrintWriter(output,true);
// to write data to server
while(b){
if (!b){
System.exit(0);
}
else {
pw.write(new Scanner(System.in).nextLine());
}
}
// to read data from server
InputStream input = s.getInputStream();
InputStreamReader isr = new InputStreamReader(input);
BufferedReader br = new BufferedReader(isr);
String data = null;
while ((data = br.readLine())!=null){
// Print it using sysout, or do whatever you want with the incoming data from server
}
}
}
Server side code:
import java.io.*
import java.net.*;
public class ServerTest {
ServerSocket s;
public void go() {
try {
s = new ServerSocket(44457);
while (true) {
Socket incoming = s.accept();
Thread t = new Thread(new MyCon(incoming));
t.start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
class MyCon implements Runnable {
Socket incoming;
public MyCon(Socket incoming) {
this.incoming = incoming;
}
#Override
public void run() {
try {
PrintWriter pw = new PrintWriter(incoming.getOutputStream(),
true);
InputStreamReader isr = new InputStreamReader(
incoming.getInputStream());
BufferedReader br = new BufferedReader(isr);
String inp = null;
boolean isDone = true;
System.out.println("TYPE : BYE");
System.out.println();
while (isDone && ((inp = br.readLine()) != null)) {
System.out.println(inp);
if (inp.trim().equals("BYE")) {
System.out
.println("THANKS FOR CONNECTING...Bye for now");
isDone = false;
s.close();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
try {
s.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
e.printStackTrace();
}
}
}
public static void main(String[] args) {
new ServerTest().go();
}
}