I'm creating a NetUtils class which extends thread to handle socket communications in a GUI without blocking the main thread. My code looks like the following (assume all import are accounted for):
Main method
public static void main(String[] args) {
EventQueue.invokeLater( () -> {
new Window().setVisible(true);
});
}
Window class
public class Window { // normally would extend JFrame bc this is a gui
// ...
NetUtils comms;
public Window() {
// ...
comms = new NetUtils("192.168.1.1", 288); // this ip/port info works fine
comms.start();
// ...
}
// other methods....
}
NetUtils class
public class NetUtils extends Thread {
private String ip;
private int port;
public NetUtils(String ip, int port) {
this.ip = ip;
this.port = port;
}
#Override
public void run() {
try (Socket socket = new Socket()) {
socket.connect(new InetSocketAddress(ip, port), 10000); // timeout 10s
System.out.println("Socket started: " + socket); // correctly prints
while (true) { // during the life of the thread
String line = readLine(socket); // throws SocketException here (socket closed error)
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
private String readLine(Socket socket) {
// uses inputstream to read bytes and such
String line;
boolean isDone = false;
while (!isDone) {
try (InputStreamReader isr = new InputStreamReader(socket.getInputStream))) {
if (isr.ready()) {
line += (char) isr.read();
}
if (!isr.ready() && line != "") {
isDone = true;
}
} catch (IOException e) {
e.printStackTrace();
}
}
return line;
}
}
What am I doing that would cause the socket to close? I ran the NetUtils code directly in the main method (I didnt separate out the readLine method) and it ran as I expected it to which lead me to believe the problem has to do with the socket being in a thread. Thanks for the help.
Clearly 'this part works' is closing the socket or its input or output stream.
NB You aren't checking for end of stream in the code you posted. I don't see the need for the readLine() method. Just replace your loop with this:
BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String line;
while ((line = reader.readLine()) != null)
{
System.out.println(line);
}
reader.close();
[exception handling omitted.]
Related
I am in the process of building a client that connects to a server and sends messages. I have that part down, the server is getting the messages, but the issue I have is having my client listen for messages from the server. Essentially it is like a chat room where I will have to send messages to the server, and my client also needs to receive messages from the server and print them out as the server sends them.
I did not build the server, or have access to the server code, but I do know the server works. Below is what I have for the Client, the SendThread is working just fine, but when I add a GetThread, the send thread no longer works so I can not get 2 threads working, one listening and one sending.
Client.java
public class Client {
public static void main(String[] args) throws IOException {
// String name = args[0];
String name = "Brandon";
Socket socket = new Socket("localhost", 4688);
Thread sendThread = new SendThread(socket, name);
Thread getThread = new GetThread(socket);
sendThread.start();
getThread.start();
}
}
SendThread.java
public class SendThread extends Thread {
Socket socket;
String name;
SendThread(Socket s, String n) {
socket = s;
this.name = n;
}
public void run(){
try{
String message;
PrintWriter printWriter = new PrintWriter(socket.getOutputStream(), true);
printWriter.println("connect Brandon");
BufferedReader bufferedReaderFromClient = new BufferedReader(new InputStreamReader(socket.getInputStream()));
System.out.println(bufferedReaderFromClient.readLine());
BufferedReader bufferedReader = new java.io.BufferedReader(new InputStreamReader(System.in));
while(true) {
String readerInput = bufferedReader.readLine();
printWriter.println(name + ": " + readerInput);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
GetThread.java
public class GetThread extends Thread {
Socket socket;
GetThread(Socket s) {
socket = s;
}
public void run(){
try{
String message;
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
while((message = bufferedReader.readLine()) != null) {
System.out.println("Incoming: " + message);
}
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Don't create a second BufferedReader. Use the same one for the life of the socket. You are losing data that the first reader has already buffered.
You need to break out of your read loop if readLine() returns null.
Looks like a race condition. readLine() is blocking until a message is sent, and when that happens, either GetThread or SendThread will grab it, leaving the other waiting once more. If you need the message in both threads, to avoid concurrency problems you should consider a monitor:
public class Monitor {
private String msg;
private boolean hasMsg = false;
public synchronized void newMsg(String msg) {
this.msg = msg;
hasMsg = true;
notifyAll();
}
public synchronized String getMsg() {
try {
while (!hasMsg) wait();
} catch (InterruptedException e) {};
hasMsg = false;
return msg;
}
}
public class Client {
// ...
Monitor m = new Monitor();
Thread sendThread = new SendThread(m, socket, name);
Thread getThread = new GetThread(m, socket);
// ...
}
public class GetThread extends Thread {
private Monitor monitor;
private Socket socket;
public GetThread(Monitor m, Socket s) {
monitor = m;
socket = s;
}
public void run() {
// ...
while((message = bufferedReader.readLine()) != null) {
monitor.newMsg(message);
System.out.println("Incoming: "+message);
}
// ...
}
}
public class SendThread extends Thread {
private Socket socket;
private Monitor monitor;
private String name;
public SendThread(Monitor m, Socket s, String n) {
monitor = m;
socket = s;
name = n;
}
public void run() {
// ...
String readerInput = monitor.getMsg();
printWriter.println(name + ": "+readerInput);
// ...
}
}
I have a socket client sending text to a socket server but the ReadLine doesnt seem to wait to receive a line before proceeding. Here is the of the server receiving the text:
public void run() {
try {
serveurSocket = new ServerSocket(PORT_ID);
connexionSocket = serveurSocket.accept();
BufferedReader reader = new BufferedReader(new InputStreamReader(connexionSocket.getInputStream()));
PrintWriter writer = new PrintWriter(connexionSocket.getOutputStream(), true);
messageRecu = "";
while (true) {
messageRecu = reader.readLine();
messageRecu = messageRecu.toUpperCase();
writer.println(messageRecu);
}
//reader.close();
//writer.close();
} catch (IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
After establishing the socket between client and server, the execution halts at reader.readLine until I send manually a string thru the socket. Which is normal and wanted. Codes resumes and its fine until its loops back to reader.ReadLine() where it will read a "null" line instead of waiting for input from the socket like it did the first time... this will obviously mess up the next command to uppercase. So how can I fix this?
EDIT: I'll add the client side if that can help understand.
public class ClientSocket {
private Socket clientSocket;
public boolean isClosed() { return clientSocket.isClosed(); }
public boolean connectToSocket (String ip, int port) {
try {
clientSocket = new Socket(ip, port);
return true;
}
catch (IOException e) {
System.out.println(e);
return false;
}
}
public String sendToServer(String messageClient) {
String messageRecu = "";
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
PrintWriter writer = new PrintWriter(clientSocket.getOutputStream(), true);
writer.println(messageClient);
messageRecu = reader.readLine();
reader.close();
writer.close();
return messageRecu;
}
catch (IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
return messageRecu;
}
}
}
A button press will call "connectTosocket" to initiate the socket. A second button when pressed will send the content of a textfield using "sendToServer".
Server does receive the message and return it capitalized but I wish for the socket to remain open with the server and if I send an other string for the same sequence to happen. Not even sure it can be done :(
According to the documentation of BufferedReader#readLine, a null is returned if the end of stream has been reached.
Change your reading loop to :
while ((messageRecu = reader.readLine()) != null) {
messageRecu = messageRecu.toUpperCase();
writer.println(messageRecu);
}
//Get out of the loop when the end of stream is reached.
As per Reading from and Writing to a Socket chapter of the Java tutorial.
As a side note, while(true) loops are not really appreciated.
The "null" signals for end of connection from the client side - which is why the connection disconnects. If you want to support multiple requests, you should run a new ServerSocket.accept() each time and wait for a new client to connect.
KKMultiServer class:
import java.net.*;
import java.io.*;
public class KKMultiServer {
public static void main(String[] args) throws IOException {
if (args.length != 1) {
System.err.println("Usage: java KKMultiServer <port number>");
System.exit(1);
}
int portNumber = Integer.parseInt(args[0]);
boolean listening = true;
try (ServerSocket serverSocket = new ServerSocket(portNumber)) {
while (listening) {
new KKMultiServerThread(serverSocket.accept()).start();
}
} catch (IOException e) {
System.err.println("Could not listen on port " + portNumber);
System.exit(-1);
}
}
}
KKMultiServerThread class:
import java.net.*;
import java.io.*;
public class KKMultiServerThread extends Thread {
private Socket socket = null;
public KKMultiServerThread(Socket socket) {
super("KKMultiServerThread");
this.socket = socket;
}
public void run() {
try (
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
) {
String inputLine, outputLine;
KnockKnockProtocol kkp = new KnockKnockProtocol();
outputLine = kkp.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = kkp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye"))
break;
}
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
You can read more about sockets in Oracle tutorials
I am very new to sockets and was hoping someone could help me. I had something working but it was not sending information very quickly so i have refactored and now cannot get back to anything which works. The issue seems to be that only the first message that is published is read and then the receiver sits on client = listener.accept(); even though im pretty sure the sender is still sending messages
Can anyone see what i might be doing wrong here please?
Thanks
public class Sender {
Socket server = null;
DataInputStream inp = null;
PrintStream outp = null;
public Sender(){
server = new Socket("127.0.0.1" , 3456);
outp = new PrintStream(server.getOutputStream());
}
private void connectAndSendToServer(String message) {
outp = new PrintStream(server.getOutputStream());
outp.print(message + "\n");
outp.flush();
}
}
Receiver class
public class Receive{
public String receiveMessage(int port) {
String message= null;
ServerSocket listener = null;
Socket client = null;
try{
listener = new ServerSocket(port);
client = listener.accept();
BufferedReader br = new BufferedReader(new InputStreamReader(client.getInputStream()));
return br.readLine();
}
...
finally{
try {
if(client!=null && listener!=null){
client.close();
listener.close();
}
}
catch (IOException e) {
}
}
return message;
}
}
This because a ServerSocket is used as an entry point for a normal Socket. accept() is a blocking operation that is usually done on a different thread compared to the one that receives/sends data to normal Socket. It sits there and waits for a new connection to spawn a new Socket which is then used for data.
This means that while receiving messages you should call just readLine() to read from the specific Socket. Having an accept inside the receiveMessage is wrong just because it's a different operation and it's even blocking.
Socket socket = serverSocket.accept();
ClientThread thread = new ClientThread(socket);
class ClientThread extends Thread {
Socket socket;
public void run() {
while (!closed) {
String line = reader.readLine();
...
}
}
You don't need to have a thread for every client though, but you need at least two for sure if you want to make your server accept a number of connections greater than 1.
You are not using ServerSocket correctly. You shouldn't create a new instance for every message but use it as a data member maybe and run an infinite loop to get a new client socket connection. Because you create it locally, the socket is closed since the object is no longer used and referenced (and so GC'ed), when you return from the method.
Something like (< condition met > is pseudo-code defines your condition to accept new connections):
while(< condition met >) {
try {
client = listener.accept();
BufferedReader br = new BufferedReader(new InputStreamReader(client.getInputStream()));
String str = br.readLine();
//do something with str
} finally {
//close client socket
}
}
Better approach will be to handle client socket in a different thread so the main thread is back to accept while you can do anything with the client socket in parallel.
Try this basic Chatting Server written by me. This server simply keeps running in loop and broadcast the message send by the clients to all the other clients associated with this server.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
public class Server {
// ///----------------------------------------Instance Variable Fields
ServerSocket ss = null;
Socket incoming = null;
// ///----------------------------------------Instance Variable Fields
// ///---------------------------------------- static Variable Fields
public static ArrayList<Socket> socList = new ArrayList<Socket>();
// ///---------------------------------------- static Variable Fields
public void go() {
try {
ss = new ServerSocket(25005);
while (true) {
incoming = ss.accept();
socList.add(incoming);
System.out.println("Incoming: " + incoming);
new Thread(new ClientHandleKaro(incoming)).start();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
ss.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
class ClientHandleKaro implements Runnable {
InputStream is = null;
OutputStream os = null;
InputStreamReader isr = null;
BufferedReader br = null;
PrintWriter pw = null;
boolean isDone = false;
Socket sInThread = null;
public ClientHandleKaro(Socket sxxx) {
this.sInThread = sxxx;
}
#Override
public void run() {
if (sInThread.isConnected()) {
System.out.println("Welcamu Clienta");
System.out.println(socList);
}
try {
is = sInThread.getInputStream();
System.out.println("IS: " + is);
isr = new InputStreamReader(is);
br = new BufferedReader(isr);
os = sInThread.getOutputStream();
pw = new PrintWriter(os, true);
String s = new String();
while ((!isDone) && (s = br.readLine()) != null) {
String[] asx = s.split("-");
System.out.println("On Console: " + s);
// pw.println(s);
Thread tx = new Thread(new ReplyKaroToClient(s,
this.sInThread));
tx.start();
if (asx[1].trim().equalsIgnoreCase("BYE")) {
System.out.println("I am inside Bye");
isDone = true;
}
}
} catch (IOException e) {
System.out.println("Thanks for Chatting.....");
} finally {
try {
Thread tiku = new Thread(new ByeByeKarDo(sInThread));
tiku.start();
try {
tiku.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Accha to hum Chalte hain !!!");
System.out.println(socList);
br.close();
pw.close();
sInThread.close();
} catch (IOException e) {
}
}
}
}
class ReplyKaroToClient implements Runnable {
public String mString;
public Socket mSocket;
public ReplyKaroToClient(String s, Socket sIn) {
this.mString = s;
this.mSocket = sIn;
}
#Override
public void run() {
for (Socket sRaW : socList) {
if (mSocket.equals(sRaW)) {
System.out.println("Mai same hun");
continue;
} else {
try {
new PrintWriter(sRaW.getOutputStream(), true)
.println(mString);
} catch (IOException e) {
System.out.println("Its in Catch");
}
}
}
}
}
class ByeByeKarDo implements Runnable {
Socket inCom;
public ByeByeKarDo(Socket si) {
this.inCom = si;
}
#Override
public void run() {
try {
new PrintWriter(inCom.getOutputStream(), true)
.println("You have Logged Out of Server... Thanks for your Visit");
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
new Server().go();
}
}
I've just started with this section of the tutorial. I only have a basic understanding of what ports are, etc.
I tried to run this code:
import java.io.*;
import java.net.*;
public class EchoClient {
public static void main(String[] args) throws IOException {
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
echoSocket = new Socket("taranis", 7);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(
echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: taranis.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for "
+ "the connection to: taranis.");
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(
new InputStreamReader(System.in));
String userInput;
while ((userInput = stdIn.readLine()) != null) {
out.println(userInput);
System.out.println("echo: " + in.readLine());
}
out.close();
in.close();
stdIn.close();
echoSocket.close();
}
}
"Don't know about host: taranis.
Java Result: 1"
Is the error catch I get. From my limited understanding; is the echo-server something which exists on my machine? If that's the case, what do I need to do to get this running? Or am I way off?
Also why have they chosen "taranis" as a parameter?
Ive also replaced "taranis" with "localhost" to see what happened.
It ended up catching an IOException this time.
EDIT: So I've found that the echo server is disabled by default in win7 and have activated it. However I cant even connect to it on telnet. I think I may just be in over my head. I've also tried the sockets you have recommended with no success.
From the same tutorial:
... The Socket constructor used here requires the name of the machine and the port number to which you want to connect. The example program uses the host name taranis. This is the name of a hypothetical machine on our local network. When you type in and run this program on your machine, change the host name to the name of a machine on your network. Make sure that the name you use is the fully qualified IP name of the machine to which you want to connect. The second argument is the port number. Port number 7 is the port on which the Echo server listens.`
In any case, you will probably want to change taranis to "localhost" and make sure an echo service is running on your machine. If it's not, you could use something like the following code to simulate an echo server.
import java.net.Socket;
import java.util.Formatter;
import java.util.Scanner;
import java.io.IOException;
import java.net.ServerSocket;
import java.util.ArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class EchoServer {
public static void main(String[] args) {
try {
new EchoServer(INSERTPORT).execute();
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
}
private ServerSocket serverSocket;
private int port;
private ArrayList<Client> clientList;
private ExecutorService clientRunner;
public EchoServer(int port) throws IOException {
this.port = port;
serverSocket = new ServerSocket(port);
clientRunner = Executors.newCachedThreadPool();
clientList = new ArrayList<>();
}
public void sendMessageToAll(String message) {
for (Client c : clientList) {
c.displayMessage(message);
}
}
public void execute() throws IOException {
while (true) {
clientList.add(new Client(serverSocket.accept(), this));
clientRunner.execute(clientList.get(clientList.size()-1));
}
}
private class Client implements Runnable {
private Socket clientSocket;
private Scanner input;
private Formatter output;
public Client(Socket s) throws IOException {
clientSocket = s;
input = new Scanner(clientSocket.getInputStream());
output = new Formatter(clientSocket.getOutputStream());
}
public void displayMessage(String s) {
output.format(s + "\n");
output.flush();
}
#Override
public void run() {
while(clientSocket.isConnected()) {
if(input.hasNextLine()) {
sendMessageToAll(input.nextLine());
}
}
}
}
}
Edit: Just for completeness, as you mentioned some problems running the code, you run the server (this code) and leave it running in the background, then run the client (the code you posted). I tested it, works fine.
Try this,
Use the loopback address of 127.0.0.1 instead of taranis.
Use port higher than 1024, something like 4444, 8333 etc....
I am also adding my code that i used to learn Client Server Commnu
Client Side Code:
public class ClientWala {
public static void main(String[] args) throws Exception{
Boolean b = true;
Socket s = new Socket("127.0.0.1", 4444);
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:
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'm trying to write a little SocketServer and a fitting ClientApplet. The connection works (I echo out incoming/closing connections), but the server does not get any InputStream.
I just can't fix the problem and feel a bit lost :/
The complete project is here.
Here is the responsible part of my server:
MessageService.java
public class MessageService implements Runnable {
private final Socket client;
private final ServerSocket serverSocket;
MessageService(ServerSocket serverSocket, Socket client) {
this.client = client;
this.serverSocket = serverSocket;
}
#Override
public void run() {
PrintWriter out = null;
BufferedReader in = null;
String clientName = client.getInetAddress().toString();
try {
out = new PrintWriter(new OutputStreamWriter(client.getOutputStream()));
in = new BufferedReader(new InputStreamReader(client.getInputStream()));
String line;
System.out.println("Waiting for "+clientName);
/* HERE I TRY TO GET THE STREAM */
while((line = in.readLine()) != null) {
System.out.println(clientName + ": " + line);
out.println(line);
out.flush();
}
}
catch (IOException e) {
System.out.println("Server/MessageService: IOException");
}
finally {
if(!client.isClosed()) {
System.out.println("Server: Client disconnected");
try {
client.close();
}
catch (IOException e) {}
}
}
}
}
Part of Client
QueueOut.java
public class QueueOut extends Thread {
Socket socket;
public ConcurrentLinkedQueue<String> queue;
PrintWriter out;
public QueueOut(Socket socket) {
super();
this.socket = socket;
this.queue = new ConcurrentLinkedQueue<String>();
System.out.print("OutputQueue started");
}
#Override
public void start() {
try {
out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
System.out.println("Running outputqueue");
while(true) {
if(this.queue.size() > 0) {
String message = this.queue.poll();
System.out.println("Sending "+message);
out.println(message+"\n");
}
}
}
catch (IOException ex) {
System.out.println("Outputqueue: IOException");
}
}
public synchronized void add(String msg) {
this.queue.add(msg);
}
}
I have reduced my post to the (as i think) necessary parts :)
Try getting your input stream before you get the output stream, even though you're not using it, you should match the inverse order on your client and your server (as discussed in another similar threads).
Edit:
Also see Socket programming
Good Luck!