I'm working on a java server-client based file transfer over socket project, I'll sum up the project shortly, I have text files related to server and client, server related text contains which ports are going to be opened and client text contains the IP and port to be connected on(server side is like 4444 and client side is like 4444 localhost) The file transfer on a single client is running pretty ok, now I'm working on second client connection and transfer, what I'm trying to do is; when a second client is run, it will read the first line of the text file (which is already in use by the first client), I thought a recursion will solve the problem but seems I couldn't figure out what I've done wrong, below are the code snippet from client side
boolean connected = false;
private void connection() {
while (!connected) {
try {
FileReader fr = new FileReader("c_input.txt");
BufferedReader br = new BufferedReader(fr);
String line = br.readLine();
String delims = "[ ]";
String[] elements = new String[8];
elements = line.split(delims);
serverPort = Integer.parseInt(elements[portIndex]);
hostIP = elements[ipIndex];
clientSocket = new Socket(hostIP, serverPort);
is = clientSocket.getInputStream();
if (is != null) {
connected = true;
System.out.println("connected to " + hostIP + " from port "
+ serverPort);
br.close();
fr.close();
} else {
System.out.println("The port " + serverPort
+ " is occupied, now trying another port.");
portIndex = portIndex + 2;
ipIndex = ipIndex + 2;
connection();
}
} catch (NumberFormatException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
System.exit(0);
}
}
}
I used recursion there, because if a port is bound by another client it has to read another line from text file and split and retry connection with the new line's inputs.(in terms short the whole method will run again) But when it comes to running, the first client connects and when second one tries to connect from same port with client1 the code still gets in if loop instead of getting in else block (I get the message from the if check's println on the console and by the way is in the if check stands for InputStream) which means there is a stream coming from server, is this normal? if so how can I achieve the whole thing connection method does all over again if the port is bound by another client?
Related
I was given the below code by my teacher for a class. I ran it one or twice and it worked fine. However I suddenly cannot get it to run from the command prompt on Windows 8 anymore. No matter what port I specify it just prints "Opening port..." and never continues. No exception is ever thrown. I have disabled my firewall and antivirus and it does not seem to work. I have added a print statement as the first line of the try catch block and it will print but it just will not create the new Socket. I am sure it is something in my Windows settings but I am unsure as to what or how to resolve it.
// Server program
// File name: "TCPServer.java"
import java.io.*;
import java.net.*;
public class TCPServer
{
private static ServerSocket servSock;
public static void main(String[] args)
{
System.out.println("Opening port...\n");
try{
// Create a server object
servSock = new ServerSocket(Integer.parseInt(args[0]));
}
catch(IOException e){
System.out.println("Unable to attach to port!");
System.exit(1);
}
do
{
run();
}while (true);
}
private static void run()
{
Socket link = null;
try{
// Put the server into a waiting state
link = servSock.accept();
// Set up input and output streams for socket
BufferedReader in = new BufferedReader(new InputStreamReader(link.getInputStream()));
PrintWriter out = new PrintWriter(link.getOutputStream(),true);
// print local host name
String host = InetAddress.getLocalHost().getHostName();
System.out.println("Client has estabished a connection to " + host);
// Receive and process the incoming data
int numMessages = 0;
String message = in.readLine();
while (!message.equals("DONE"))
{
System.out.println(message);
numMessages ++;
message = in.readLine();
}
// Send a report back and close the connection
out.println("Server received " + numMessages + " messages");
}
catch(IOException e){
e.printStackTrace();
}
finally{
try{
System.out.println("!!!!! Closing connection... !!!!!\n" + "!!! Waiting for the next connection... !!!");
link.close();
}
catch(IOException e){
System.out.println("Unable to disconnect!");
System.exit(1);
}
}
}
}
This code works fine. The problem is the code for the client. The answer to your problem is already written in a comment in your code.
// Put the server into a waiting state
link = servSock.accept();
The server goes into a waiting state until it gets a connection. The client is the one that would be getting the error since it did not connect. If the client was working correctly the code would continue and you would get the additional output.
I have developed a simply video game and I want to update it with the multiplayer functionality using websockets. I want to have two versions of the game. The first one to work as server and the other version as a client. I want to initialize the game from the server and to wait for the reaction of the client. My first question: is it possible to run server and client in the same machine (give as an input the same ip)? Secondly I am using the following code in order to create the sockets from the server side:
try {
serverSocket = new ServerSocket(10007);
}
catch (IOException e)
{
System.err.println("Could not listen on port: 10007.");
System.exit(1);
}
System.out.println ("Waiting for connection.....");
try {
clientSocket = serverSocket.accept();
}
catch (IOException e)
{
System.err.println("Accept failed.");
System.exit(1);
}
System.out.println ("Connection successful");
When I am trying to connect from the client it seems that the whole thing its not working as i am receiving the message waiting for connection.... My code for connecting the client is the following:
String serverHostname = new String("ip");
if (args.length > 0)
serverHostname = args[0];
System.out.println("Attemping to connect to host " +
serverHostname + " on port 10007.");
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
echoSocket = new Socket(serverHostname, 10007);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(
echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: " + serverHostname);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for "
+ "the connection to: " + serverHostname);
System.exit(1);
}
What can it be the issue here?
Your Server Side Code is fine. just a little note here, the ServerSocket.accept(); method is ablocking call, meaning that program execution will halt there until a client connects to it.
Secondly i can see an issue from the first line of your client code below
if (args.length > 0)
serverHostname = args[0];
args[0] may not be an ip address, i'm not too sure about how java command line applications behave but in c++ for instance, args[0] in the right context is always the absolute path of the program executable. this may be the case in java too.
So you may be passing an ip address but will actually be passed in as args[1].
I have a method which takes an IP, receives data and stores it in a List. At the end of the method it returns this List. However when this method is called, the list is empty. I think it is a really simple fix and it's me being stupid but could anyone point me to where I have gone wrong so I dont do it again?
public List<String> receiveDataFromOperator(){
List<String> dataRec = new ArrayList<String>();
try
{
System.out.println("Client Program");
//Hard coded IP Address
String ip = "146.176.226.147";
//Hard coded port
int port = 500;
// Connect to the server
Socket sock = new Socket(ip, port);
// Create the incoming stream to read messages from
DataInputStream network = new DataInputStream(sock.getInputStream());
// Display our address
System.out.println("Address: " + sock.getInetAddress());
String line;
// Loop until the connection closes, reading from the network
while ((line = network.readUTF()) != null)
{
dataRec.add(line);
}
sock.close();
}
catch (IOException ioe)
{
//Test output for the arraylist size
System.out.println(dataRec.size());
for(int i = 0; i<dataRec.size(); i++){
System.out.println("Line " + i + dataRec.get(i) + "\n");
}
}// End of catch
return dataRec;
}//End of method
If the server is writing binary data with DataOutputStream.writeUTF() it should work.
If you are sending text from the server you need to read text from the socket with BufferedReader.readLine().
BTW: When you get an IOException you generally shouldn't ignore it and pretend it didn't happen esp. when the program is not behaving as you expect.
In the code below, what determines what will be sent back to the client (the PHP page). I am trying to alter this so that it sends a variable back to the PHP page with an error message that is defined based on actions made in my java code.
Edit: To answer some questions, what I am trying to do is this.
Send a string to the java script with a socket and convert it to a variable to be used in the java script. It will run through some if statements and I need to set the error statements to a variable lets say "reply". I need to send "reply" then back to the PHP file.
public class MyJavaServer {
public static void main(String[] args) {
int port = 20222;
ServerSocket listenSock = null; //the listening server socket
Socket sock = null; //the socket that will actually be used for communication
try {
listenSock = new ServerSocket(port);
while (true) { //we want the server to run till the end of times
sock = listenSock.accept(); //will block until connection recieved
BufferedReader br =
new BufferedReader(new InputStreamReader(sock.getInputStream()));
BufferedWriter bw =
new BufferedWriter(new OutputStreamWriter(sock.getOutputStream()));
String line = "";
while ((line = br.readLine()) != null) {
bw.write("PHP said: " + line + "\n");
bw.flush();
}
//Closing streams and the current socket (not the listening socket!)
bw.close();
br.close();
sock.close();
}
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
If I get your question right, the line where the answer gets sent to the peer is
bw.write("PHP said: " + line + "\n");
which writes the given string to bw.
i have a java client-server app in java, both using the same connection class that contains both send/receive messages.
for some reason, some of the messages i send are received in a malformed order:
here's the code
//set up
_in = new BufferedReader(new InputStreamReader(this._socket.getInputStream()));
_out = new BufferedWriter(new OutputStreamWriter(this._socket.getOutputStream()));
this._socket.setSoTimeout(S_TIMEOUT);
public synchronized boolean send(String message){
try {
_out.write(message);
_out.write(Connection.DELIMITER);
_out.flush();
return true;
} catch (IOException e) {
}
return false;
}
public String receive(){
int c;
try {
String message = "";
System.out.println("Getting message:");
c = _in.read();
while(c != -1 && c != Connection.DELIMITER) {
message += (char) c;
c = _in.read();
}
if (c == -1) {
return null;
}
return message;
} catch (IOException e) { }
return null;
}
some messages, for example "new_order" will might return with "ew_ord".
some characters are lost, others are sent separately. this seems odd as its TCP
could this be an encoding related issue?
Delimiter is (char) 0
socket timeout is 20000 (ie 20 senconds). every 10 seconds i send an empty message to make sure socket does not close
EDIT:
although it was solved using the Scanner, i must say that the original code worked fine for many messages/various machines for a very long time (a few weeks), and then suddenly failed to work with one specific message on one specific machine (other messages went through just fine). i've done socket data transfer in java MANY times and i've written many read/write methods to handle the sockets. it's the first time i ran into this.
although in the original code i set the encoding (in the posted code i didn't), i believe that the problem was encoding related. at one point, the message that was received had every second character missing. afterwards i changed it a bit, and the first/second character of the message were received in a separate message. from my understanding, it's either an encoding issue or some firewall/other security program that was running on the message sender machine, that decided to filter outgoing packets.
Try replacing your receive with a Scanner and let it do the work for you.
// in your setup
Scanner sc = new Scanner(_in).useDelimiter(Connection.DELIMETER);
public String receive() {
try {
return sc.next();
} catch(IOException e) {
return "";
}
}
For starters, I would make sure you're printing exceptions in those catch blocks.
Then, you're using the platform default encoding for converting characters to bytes. If these two processes are running on different machines, it's possible they're using different encodings. I would make sure you're specifying an encoding when you set up the Reader and Writer.
You can use UTF encoding for getting Full String of Message.
U can try this code and I am Sure About this code because i used it in My Chat Application.
String data=" ";
socket = new Socket("localhost",999);
while(true)
{
dos = new DataOutputStream(socket.getOutputStream());
dis = new DataInputStream(socket.getInputStream());
data = dis.readUTF();
jta.append(data +"\n");
}
Where jta is JTextArea.
It's for Client Side
Now For Server Side:
try
{
server = new ServerSocket(999);
Socket soc = server.accept();
while(true)
{
String data="";
try
{
dis = new DataInputStream(soc.getInputStream());
dos = new DataOutputStream(soc.getOutputStream());
data = dis.readUTF();
}
catch(Exception e)
{ }
jta.append(data + "\n");
}
}
catch (IOException e)
{
JOptionPane.showMessageDialog(this, e);
System.exit(-1);
}