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();
}
}
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/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 have a basic GUI in Java where there is a JButton,I have given a functionality to start the Server with that button. But when I click the button the program freezes. Is it because of the while loop? If so how can I overcome this?
Server Code
void connect_clients()
{
try {
ServerSocket listener = new ServerSocket(7700);
try {
while (true) {
Socket socket = listener.accept();
try {
PrintWriter out =
new PrintWriter(socket.getOutputStream(), true);
out.println(new Date().toString());
}
finally {
socket.close();
}
}
}
finally {
listener.close();
}
}
catch (IOException ex) {
Logger.getLogger(Test_Frame.class.getName()).log(Level.SEVERE, null, ex);
}
}
Your program is freezing because you are blocking the UI thread. You need to post this on a separate thread:
public void postListen()
{
new Thread(new Runnable()
{
public void run()
{
connect_clients();
}
}).start();
}
Call that method instead and it should run the connect_clients() method on a separate thread. The new thread will block until a client connects.
Here is method explanation of ServerSocket.accept():
Listens for a connection to be made to this socket and accepts it. The
method blocks until a connection is made.
Until there is data input to socket, your program will freeze. If it's another problem, please check your logs. There may be another problem.
I've got an UDP server class which implements Runnable interface. I start it in the thread.
The problem is that I can't stop it. Even in Debug it stops on pt.join() method.
Here is my server class
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
public class Network implements Runnable {
final int port = 6789;
DatagramSocket socket;
byte[] input = new byte[1024];
byte[] output = new byte[1024];
public Network() throws SocketException{
socket = new DatagramSocket(6789);
}
#Override
public void run() {
while(true){
DatagramPacket pack = new DatagramPacket(input,input.length);
try {
socket.receive(pack);
} catch (IOException e) {
e.printStackTrace();
}
input = pack.getData();
System.out.println(new String(input));
output = "Server answer".getBytes();
DatagramPacket sendpack = new DatagramPacket(output,output.length,pack.getAddress(),pack.getPort());
try {
socket.send(sendpack);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
This is the main class
public class Main {
static Network network = null;
public static void main(String[] args) throws IOException{
network = new Network();
System.out.println("Try to start server");
Thread pt = new Thread(network);
pt.start();
pt.interrupt();
try {
pt.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Stop server");
}
}
How to stop server?
java.net reads are non-interruptible. You would have to either close the DatagramSocket or have it read with a timeout (setSoTimeout()), and when you get the resulting SocketTimeoutException check the interrupt status: if set, exit the thread.
Calling interrupt doesn't actually stop the thread, it just sets a flag.
Inside your loop, check for isInterrupted(). e.g., a quick and dirty way would be change
while(true)
to
while (!Thread.currentThread().isInterrupted())
But you should consult some more documentation if you get more serious about this project.
As mentioned by #EJP, if you are hanging in the Socket IO, you'll need to close the Socket or have a timeout.
In addition to what EJP said, you probably should have a local boolean called running (or whatever), and set it to true before you enter your while loop. Have your while loop be conditioned on this local boolean. And provide methods (stopServer() and isRunning()) to set and check the status of the boolean. You also might want to remove the try-catch from inside the while loop and put the entire while loop within a try-catch-finally and in the finally statement perform clean-up (set running=false; close the connection, etc)
here's a little code I wrote. This next class waits for a connection and creates a new thread upon receiving one:
ServerSocket serverSocket = null;
ExecutorService serv = Executors.newCachedThreadPool();
serv.execute(new UserThread());
try {
serverSocket = new ServerSocket(FMDataManager.getPort());
serverSocket.setSoTimeout(0);
while (_listening){
System.out.println("Listening on port "+FMDataManager.getPort());
System.out.println("Waiting for connections.");
serv.execute(new UploadThread(serverSocket.accept()));
}
} catch (IOException e) {
System.err.println("Could not listen on port: "+FMDataManager.getPort()+".");
System.exit(-1);
}
as you can see i am using ServerSocket.accept() method to wait for a connection.
The thread is indeed created, but it won't run. I put a little "thread created" in its constructor and another message "starting thread" in run(), but I only got the first message. After that it didn't do anything, I didn't even get "thread created".
Any ideas please?
I've add the implementation of the UploadThread I am trying to start, maybe It'll help
public class UploadThread extends Thread{
Socket _socket;
public UploadThread(Socket socket) {
super("UserThread");
_socket = socket;
}
public void run(Socket socket) {
System.out.println("entred upload thread");
DataOutputStream out = null;
DataInputStream in = null;
try {
out = new DataOutputStream(_socket.getOutputStream());
in = new DataInputStream(_socket.getInputStream());
FileMessage inputMessage;
SendFile outputMessage;
inputMessage = (FileMessage) CommandEnum.readMessage(in);
System.out.println("F: "+inputMessage.getCaption());
File file = null;
Iterator<File> itr = FMDataManager.getFiles().iterator();
while (itr.hasNext()){
File temp = itr.next();
if (temp.getName().equals(inputMessage.getFile()))
file = temp;
}
outputMessage = new SendFile(file);
outputMessage.send(out);
} catch (IOException e) {
e.printStackTrace();
} finally{
try {
_socket.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
Try serv.submit instead of serv.execute.
EDIT
Looks like UploadThread isn't overriding run() correctly. That being said, your run method declaration should look like this:
#Override
public void run(){
//do stuff
}
There's no need to pass socket as an argument.
As indicated by sthupahsmaht's comment your UploadThread implementation is wrong. The signature for the run() method is public void run(). Currently you are creating a new method with the signature public void run(Socket). As run() doesn't take any arguments you have to pass all parameters via the constructor or setters.
There are two best practices that can help you avoid such mistakes in the future:
Whenever you implement or override a method, annotate it with #Override. If you create a new method with #Override, the compiler signals an error.
Don't extend Thread but implement Runnable. Thread has a default implementation for run() which does nothing. This is what happens with your code currently.
Without seeing the part of the code that actually constructs the thread, I'll guess you're NOT calling the 'start()' method on the thread object.
Needs to be something like this:
Thread thr = new Thread(new Runnable() { void run() { /* do stuff */ }) ;
thr.start() // GO!