I am having problem even with this very basic client-server application. The client is not sending data/ the server is not receiving. I cannot understand where is the problem. I am even starting to think that i did not understand anything about sockets.
This is the Server code:
public class Server
{
public static void main(String args[])
{
try{
ServerSocket serverSocket = new ServerSocket(3000);
Socket socket = serverSocket.accept();
System.out.println("Client connected: "+socket.getInetAddress.toString());
Scanner scanner = new Scanner(socket.getInputStream());
while(true)
{
System.out.println(scanner.nextLine());
}
}catch(IOException e)
{
System.out.println("error");
}
}
}
This is the client code:
public class Client
{
public static void main(String args[])
{
Socket socket;
PrintWriter printWriter;
try {
socket = new Socket("127.0.0.1", 3000);
printWriter = new PrintWriter(socket.getOutputStream(), true);
while(true)
{
printWriter.write("frejwnnnnnnnnnnnnnnnnnnnnnnnnosfmxdawehtcielwhctowhg,vort,hyvorjtv,h");
printWriter.flush();
}
}catch(IOException e)
{
System.out.print("error\n");
}
}
}
If I run both on the same machine, the server prints correctly "client connected .....", but then prints no more.
What is the problem?
The server reads the next line. The client doesn't send any line ending. So the server can't possibly know that the line is supposed to be ended, and blocks until it finds an EOL in the stream. Or until the client closes its socket.
In client code, you decorate your output stream with PrintWriter, so you can use println.
Replace
printWriter.write("frejwnnnnn...rjtv,h");
printWriter.flush();
by:
printWriter.println("frejwnnnnn...rjtv,h");
Flush is useless since have request autoflush (true in PrintWriter constructor).
In server code, you can use a BuffererdReader decorator instead of Scanner:
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String inputLine;
while ((inputLine = br.readLine()) != null) {
System.out.println(inputLine);
}
Related
I am trying to set up a server with a client and a handler. The client should ask for a string from the user. This should then be written to an OutputStream, get read in by the handler which then saves the string to its own OutputStream before passing it back to the client. I know that this program is completely pointless, I am just trying to get my head around how servers, clients and handlers work.
Here is my code so far:
Server
public class Server {
public static void main (String args[]) throws IOException {
int port = 8080;
ServerSocket server = new ServerSocket(port);
while (true) {
System.out.println("Waiting for client...");
Socket client = server.accept();
System.out.println("Client from "+client.getInetAddress()+" connected.");
Handler handler = new Handler(client);
handler.run();
}
}
}
Handler
class Handler extends Thread {
private Socket client;
public Handler(Socket c) {
client = c;
}
public void run() {
try {
Thread.sleep(3000);
System.out.println("1");
PrintWriter out = new PrintWriter(new OutputStreamWriter(client.getOutputStream()));
BufferedReader in =
new BufferedReader(new InputStreamReader(client.getInputStream(),
"UTF-8"));
System.out.println("2");
String message = in.readLine();
System.out.println("4");
System.out.println("5");
out.println(message);
out.flush();
client.close();
System.out.println("Finish");
} catch (IOException e1) {
e1.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
Client
public class Client {
public static void main (String args[]) throws IOException {
Socket server = new Socket("127.0.0.1", 8080);
System.out.println("Attempting connection...");
Scanner scan = new Scanner (System.in);
System.out.println("Please enter a string:");
String message = scan.next();
PrintWriter out = new PrintWriter(new OutputStreamWriter(server.getOutputStream()));
BufferedReader in =
new BufferedReader(new InputStreamReader(server.getInputStream(),
"UTF-8"));
out.println(message);
String messageReturn = in.read();
scan.close();
System.out.println("Server said: " + messageReturn);
in.close();
out.close();
}
}
The problem is that the handler seems to hang when it tries to read the message in. This problem seems similar to the one presented here: Socket problem - readline won't work properly
But this solution isn't working for me. I have tried using objectInputStreams instead of my current solution, but this didn't work either.
I doubt whether your client code will compile. The return type for this is int.
String messageReturn = in.read();
Anyway, this should work:
package network;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
public class Client {
public static void main (String args[]) throws IOException {
Socket server = new Socket("127.0.0.1", 9890);
System.out.println("Attempting connection...");
Scanner scan = new Scanner (System.in);
System.out.println("Please enter a string:");
String message = scan.next();
PrintWriter out = new PrintWriter(new OutputStreamWriter(server.getOutputStream()));
BufferedReader in = new BufferedReader(new InputStreamReader(server.getInputStream(), "UTF-8"));
out.println(message);
// NOTE this
String messageReturn = in.readLine();
scan.close();
System.out.println("Server said: " + messageReturn);
in.close();
out.close();
}
}
Note Port has been changed.
Server Output
Waiting for client...
Client from /127.0.0.1 connected.
1
Client Output
Attempting connection...
Please enter a string:
Hello
The problem might be that you do not send an escape sequence with your response. ReadLine() waits till it gets an escape. Try sending a "\n" with your response. There is an article about problems using readLine() and println() with sockets. It also shows how to solve it.
ReadLine() / Println() and sockets
So this is the first Server-Client I am trying to 'setup' but it does not work as I want it to. Here is What I want:
The Client to do: (see comments in the code for the Client)
A 'user input' should be read by the Client
Send the 'user input' to the server
receive back something from the server
The server to do: (See the comments in the code for Server)
receive the 'user input' that read by the client
Do something with the 'user input'
Send what was done in (2), back to the client.
It is not working the only right thing it is doing is that it receives the input from the 'user', that is it:
public class Cli {
BufferedReader in;
PrintWriter out;
Socket s;
public Cli(int port){
try {
s = new Socket("127.0.0.1", port);
out = new PrintWriter(s.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader
(s.getInputStream()));
} catch (UnknownHostException e) {
System.out.print("fel");
} catch (IOException e) {
System.out.print("fel");
}
}
public void startaClient(){
BufferedReader stdIn = new BufferedReader (new InputStreamReader(System.in));
try {
while(true){
String userInput = stdIn.readLine();// get the user input (1)
System.out.print("from user: " + userInput);
out.write(userInput); // sends to server (2)
System.out.println(in.readLine()); // receive from server(3)
}
} catch (Exception e){
System.out.println("fel1");
}
}
public static void main(String[] args){
Cli c=new Cli(4002);
c.startaClient();
}
Here is the code for the Server:
public class Ser {
ServerSocket s;
public Ser()throws Exception{
s = new ServerSocket(4002);
}
public void startaServern()throws Exception {
while (true) {
Socket socket = s.accept(); //waits for new clients, acceptera inkommande förfrågan
Trad t = new Trad(socket);
t.start();
}
}
public static void main(String[] args)throws Exception{
Ser b = new Ser();
b.startaServern();
}
}
public class Trad extends Thread {
Socket socket;
BufferedReader in;
PrintWriter out;
public Trad(Socket s){
socket=s;
try{
in = new BufferedReader(new InputStreamReader(socket.getInputStream())); //
out=new PrintWriter(socket.getOutputStream(),true);
}catch(Exception e){System.out.println("fel");}
}
public void run(){
while(true){
try{
String theInput = in.readLine(); //read, receive message from client (1)
String res = theInput+"blabla"; // do something with the message from the client (2)
out.write(res); // send it back to the client (3)
} catch(Exception e) {
System.out.println("fel1");
}
}
}
}
When you do readLine() it will read a line i.e. until it reaches a new line.
Unless you send a new line it will wait forever. I suggest you send a newline so the reader knows the line has ended.
Since you are using a PrintWriter the simplest solution is to use
out.println(res);
instead of out.write(res);
So i'm trying to make a server/client solution using BufferedReader and BufferedWriter, but it won't work! Using only DataInputStream and DataOutputStream worked perfectly fine, but nothing printed out with the Buffered objects. Where is my error?
public class TServer {
static final int PORT = 8001;
static final int QUEUE = 50;
public static void main(String[] args) {
try (ServerSocket serverSocket = new ServerSocket(PORT, QUEUE)) {
Socket socket = serverSocket.accept();
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
BufferedWriter output = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
System.out.println(input.readLine());
output.write("this is the server!");
output.flush();
} catch (IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
}
public class TClient {
static final String HOST = "localhost";
static final int PORT = 8001;
public static void main(String[] args) {
try (Socket socket = new Socket(HOST, PORT)) {
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
BufferedWriter output = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
output.write("this is the client");
output.flush();
System.out.println(input.readLine());
} catch (IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
}
Using only DataInputStream and DataOutputStream worked perfectly fine, but nothing printed out with the Buffered objects.
The Client is sending the following:
output.write("this is the client");
The Server is trying to read a line with the BufferedReader:
System.out.println(input.readLine());
But no line will be received as the end of line terminator is not sent (hence, the method will block (same goes for the Server, which does not send the end of line terminator)). See the API for BufferedReader, which states:
Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.
You are using readLine method of BufferedReader, so you should write newline-terminated string in corresponding BufferedWriter. Like:
output.write("this is the client");
output.newLine();
I am trying to create a multiclient chat sort of server in which we have multiple clients connecting to server and whatever message a client enters, it gets displayed to all the clients(including the client who sent the message). I am not getting this output, instead the message just echoes only on the sender client and no other client. Code is quite long, hence i am displaying snippets of whichever code i think will help you understand error. In case, it is not enough, just comment which part you require. Thanks in advance. I am stuck on this since about hour and half, so i appreciate whatever help i would get.
The Server Class
public class Multiserver {
ServerSocket serversocket;
Socket socket;
ArrayList<Socket> al = new ArrayList<Socket>();
DataInputStream dis;
DataOutputStream dos;
Multiserver() throws IOException
{
serversocket = new ServerSocket(1036);
System.out.println("Server started on port 1036");
while(true)
{
socket = serversocket.accept();
System.out.println(socket);
al.add(socket);
Mythread thread = new Mythread(socket, al);
thread.start();
}
}
Thread used in server class
public class Mythread extends Thread{
Socket socket;
ArrayList al;
DataInputStream dis;
DataOutputStream dos;
Mythread(Socket socket, ArrayList al)
{
this.socket = socket;
this.al = al;}
public void run()
{
try{
String data ="";
dis = new DataInputStream(socket.getInputStream());
data = dis.readUTF();
if(!data.equals("stop"))
{
broadcast(data);
}
else
{
dos = new DataOutputStream(socket.getOutputStream());
// data = dos.readUTF();
dos.writeUTF(data);
dos.flush();
//dos.close();
}
}
catch(Exception e){
System.out.println("Run "+e);
}
}
public void broadcast(String data)
{
try{
Iterator it = al.iterator();
while(it.hasNext())
{
Socket socket1 = (Socket)it.next();
dos = new DataOutputStream(socket1.getOutputStream());
dos.writeUTF(data);
dos.flush();
}
}
catch(Exception e){
System.out.println("Broadcast running "+ e);
}
}
}
The client class
public class Multiclient {
Socket socket;
DataInputStream dis;
DataOutputStream dos;
Multiclient() throws IOException
{
socket = new Socket("127.0.0.1", 1036);
System.out.println(socket);
Mythreadc my = new Mythreadc(socket);
my.start();
}
Thread used in client class
public class Mythreadc extends Thread{
DataInputStream dis;
DataOutputStream dos;
Socket socket;
Mythreadc(Socket socket)throws IOException
{
this.socket = socket;}
public void run()
{
BufferedReader br = null;
try{
br = new BufferedReader(new InputStreamReader (System.in));
dos = new DataOutputStream(socket.getOutputStream());
String data = "";
do{
data = br.readLine();
dos.writeUTF(data);
System.out.println(data);
dos.flush();
}
while(!data.equals("stop"));
}
catch(Exception e)
{
System.out.println("Client input "+e);
}
finally{
try{
br.close();
dis.close();
dos.close();
}
catch(Exception e)
{
System.out.println("Closing "+e);
}
}
}
}
I am sorry i have put on such a long code, almost all the program. But i feel it is necessary to understand where the problem lies.I have tried and i think it lies in the part where we display data written in the client's socket in the client thread class but i don't know what it is ???
#EDIT: Forgot to mention. The client stops when he sends the message "Stop"!
There are two problems with your code that are preventing the clients from displaying more than one message.
Problem one: Your client code never actually displays or prints out the messages it receives from the server. The line
dos = new DataOutputStream(socket.getOutputStream());
creates an OutputStream you can use to write data to the socket, i.e. send messages to the server. But you never use the socket's InputStream, which is what you need to do to read data from the socket, i.e. receive messages from the server. When you see a message printed out on the client, you're actually just seeing the result of
System.out.println(data);
which has your client print the message it just sent.
In order for the client to accept input from the user and read messages from the server at the same time, you should probably use two threads on the client. One thread can just be the client thread you already wrote, since it takes care of accepting input from the user. The other thread should look something like this:
public class ClientReaderThread extends Thread {
Socket socket;
ClientReaderThread(Socket socket) {
this.socket = socket;
}
public void run() {
try (BufferedReader serverReader = new BufferedReader(
new InputStreamReader(socket.getInputStream()))){
String fromServer = serverReader.readLine();;
while(fromServer != null) {
if (fromServer.equals("stop"))
break;
System.out.println(fromServer);
fromServer = serverReader.readLine();
}
} catch (IOException e) {
System.out.println("Client error! Got exception: " + e);
}
}
}
(Note that I use the try-with-resources statement to construct the reader, which takes care of closing it when the client stops).
Then in your main client class, start both threads with the same socket:
Multiclient() throws IOException
{
socket = new Socket("127.0.0.1", 1036);
System.out.println(socket);
Mythreadc my = new Mythreadc(socket);
ClientReaderThread reader = new ClientReaderThread(socket);
my.start();
reader.start();
}
Problem two: Your server only reads and echoes a single line from each client, because the socket thread that handles each client (Mythread) doesn't contain a loop. With your setup of creating a single thread per client, run() only gets called once per client, so that run() method needs to handle every message that client sends.
Here's how the run() method in the server's thread should look:
public void run() {
try (BufferedReader inStream = new BufferedReader(
new InputStreamReader(socket.getInputStream()))){
String data = inStream.readLine();
while(data != null) {
if(data.equals("stop"))
break;
broadcast(data);
data = inStream.readLine();
}
}
catch(Exception e){
System.out.println("Run exception "+e);
} finally {
al.remove(socket); //This is important to do
}
}
I made an additional important change here: at the end of the run() method, when either the client disconnected or an exception happened, the thread removes its socket from the ArrayList. This ensures that other server threads, which all reference the same ArrayList, don't try to broadcast to the socket of a client that has disconnected. If you neglect to do this, you'll get an exception when a client sends a message to the server after another client has disconnected.
Miscellaneous notes
As I mentioned in my comment, you should give al a type of ArrayList<Socket> inside the thread class, and use a for-each loop instead of an Iterator to iterate over it in broadcast().
I'm using BufferedReader instead of DataInputStream to read from the socket. That's because DataInputStream.readUTF() and writeUTF() are deprecated, and have been replaced with BufferedReader.readLine() and PrintWriter.println().
The streams like dis and dos don't need to be instance variables in your thread classes, since they are only ever used inside the run() method. They can be local variables inside run(), like I did with inStream in my new run() method.
I think you just missed passing the ArrayList of Sockets Users Currently Connected to The Server to the thread
and Instead of Posting your Server Class You have just posted Client Program 2 times anyway ,
Your ServerClass should be build in this way : -
As soon as ServerClass recieves the request from any client, Server Class should add the Socket into ArrayList and create New Thread and just pass both to the MyThread Class
Edit :
It seems you haven't written code for Displaying the data you will get from the server .
At Client Side for Sending the Message You can simple write that in Main Thread that is under Your Client Class's Main Mehtod
You actually needed Thread at client side not for sending the message but rather for Listening the Message from the server,
because you never known when anyone can send you the message but you will always know when you want to send message to anybody connected to this chat App
Now coming to the Coding Part :
Client Class
public class Multiclient {
Socket socket;
DataInputStream dis;
DataOutputStream dos;
Multiclient() throws IOException
{
socket = new Socket("127.0.0.1", 1036);
System.out.println(socket);
Mythreadc my = new Mythreadc(socket);
my.start();
/**
* Here write out the code for taking input from Standard Console
*/
BufferedReader br = null;
try{
br = new BufferedReader(new InputStreamReader (System.in));
dos = new DataOutputStream(socket.getOutputStream());
String data = "";
do{
data = br.readLine();
dos.writeUTF(data);
System.out.println(data);
dos.flush();
}
while(!data.equals("stop"));
}
catch(Exception e)
{
System.out.println("Client input "+e);
}
}
Client Thread
try{
String data ="";
dis = new DataInputStream(socket.getInputStream());
while(data.equalsIgnorCase("stop")){
data = dis.readUTF();
System.out.println("Server Message : "+data);
}
}
catch(Exception e){
System.out.println("Run "+e);
}
Client Thread is not complete but i think this information is sufficient enough .
Hope It help you out , Your problem do remind me of College Days :)
I'm new to the network communication and I'm trying to build client-server application.
protected void init(){
Server myServer = new Server();
Client myClient = new Client();
}
That's my Client class:
public class Client {
public Client() {
init();
}
private void init() {
Socket echoSocket = null;
DataOutputStream os = null;
DataInputStream is = null;
DataInputStream stdIn = new DataInputStream(System.in);
try {
echoSocket = new Socket("localhost", 1234);
os = new DataOutputStream(echoSocket.getOutputStream());
is = new DataInputStream(echoSocket.getInputStream());
os.writeInt(stdIn.readInt());
echoSocket.getOutputStream().close();
echoSocket.getInputStream().close();
echoSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
And that's server:
public class Server {
public Server() {
init();
}
private void init() {
try {
boolean run = true;
ServerSocket ss = new ServerSocket(1234);
Socket s = ss.accept();
DataInputStream dis = new DataInputStream(s.getInputStream());
System.out.println(dis.readInt());
s.getInputStream().close();
s.getOutputStream().close();
s.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
First of all:
Can I initialize client and server simply like i did? new Server() and new Client()?
Question 2:
Is it important what i initialize at first? client or server?
Question 3:
When i compile this code with client first initialized, i become Connection refused: connect. I know it means that there is no listening socket running on the port you are trying to connect to. That's why server must go first, i think. Is it so? can i fix it using setSoTimeout and how?
Question 4:
When i compile it with server and then client, output is nothing. And i think it has nothing to do with client, because if i try to print "1", for example, it doesn't work either. I think it just waits for the client and does nothing that goes after. How can i fix this? maybe setSoTimeout goes here too?
You can't have both client and server in the same thread.
As you already have observed, the server accepts the connection and tries to read something. It doesn't know that the client is running in the very same thread.
Either make a multi-threaded application, where client and server have their own thread. Or make two prgrams that run independently of each other. The latter would be also the "normal case".
Make two different projects, first run server than client.
Server will write on console "Server started" than run client it will ask your name, type your name press ok . Your name will be sent to server and server will reply saying hello to you.
Here is server code
import java.net.*;
import java.io.*;
import javax.swing.*;
public class Server {
public static void main(String[] args) {
try{
ServerSocket ss= new ServerSocket(2224);
System.out.println("Serever started");
while(true)
{
Socket s=ss.accept();
InputStream is=s.getInputStream();
InputStreamReader isr=new InputStreamReader(is);
BufferedReader br=new BufferedReader(isr);
OutputStream os=s.getOutputStream();
PrintWriter pw=new PrintWriter(os);
String name=br.readLine();
String message="Hello "+name+"from server";
pw.println(message);
pw.flush();
}
}
catch(Exception exp)
{
System.out.println("Excepttion occured");
}
}
}
Here is client code
import java.net.*;
import java.io.*;
import java.util.Scanner;
import javax.swing.*;
public class Client {
public static void main(String[] args) throws IOException {
Socket s=new Socket("localhost",2224);
InputStream is=s.getInputStream();
InputStreamReader isr=new InputStreamReader(is);
BufferedReader br=new BufferedReader(isr);
OutputStream os=s.getOutputStream();
PrintWriter pw=new PrintWriter(os,true);
String message = JOptionPane.showInputDialog("Give your name");
pw.println(message);
pw.flush();
String servermessage = br.readLine();
JOptionPane.showMessageDialog(null, servermessage);
s.close();
}
}