Develop Reference

Multiple threaded socket server in Java

I recently tried creating a socket server which can connect to multiple clients... I was too lazy to write a separate program for the client so I'm just using telnet.
The first time I connect(using telnet), it works fine... but the second telnet connection just hangs and the cmd screen goes blank...
Even the first connection gets hanged after sending a string.
Any help is appreciated
Here's the code:
Chatserver.java
I would really appreciate I if someone would correct the mistakes in the code and post it
You could have a look at it if you want but it might be easier if you just clicked the hyperlink and viewed the image:
package chatserver;
import java.io.*;
import java.net.*;
import java.util.logging.Level;
import java.util.logging.Logger;
class Chat extends Thread {
#Override
public void run() {
Chat server = new Chat();
try {
server.SERVER();
} catch (Exception ex) {
Logger.getLogger(Chat.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void SERVER() throws Exception {
ServerSocket SRVSOCK = new ServerSocket(8068);
Socket SOCK = SRVSOCK.accept();
InputStreamReader IR = new InputStreamReader(SOCK.getInputStream());
BufferedReader BR = new BufferedReader(IR);
PrintStream PS = new PrintStream(SOCK.getOutputStream());
PS.println("What is your name: ");
String name = BR.readLine();
String Message = BR.readLine();
PS.println(name + " : " + Message);
}
}
public class ChatServer {
public static void main(String[] args) {
Chat c1 = new Chat();
Chat c2 = new Chat();
while (true) {
c1.start();
c2.start();
}
}
}
Guys,
Today I typed up the same code in python as I am much more familiar with it than I am with Java
I have succeeded in connecting to multiple clients but am unable to see outputs from chat() yet...
I would like to know what mistake I made in this code below and would be very grateful if someone helps me transcribe it to Java:
#!/usr/bin/env python3
import socket
import threading
import time
clients = []
addr = []
HOST = '127.0.0.1'
PORT = 8068
client_no = 0
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
print('Socket bind complete')
def connect(clnt_no):
while True:
s.listen(1)
print('searching for clients')
clnt, adr = s.accept()
clients.append(clnt)
addr.append(adr)
print('connected to: ',addr[clnt_no])
# print(len(clients))
clnt_no += 1
client_no = clnt_no
def chat():
while True:
for x in range(0, client_no):
data = clients[x] = recv(1204)
if data:
for y in range(0, client_no):
clients[y].send('from client ', x, ' ', data)
else:
print('no data recieved from any client')
def Main():
conn = threading.Thread(target=connect, args=[0])
cht = threading.Thread(target=chat)
# while True:
conn.start()
cht.start()
if(__name__ == '__main__'):
Main()
Thanks in advance

Two problems:
First, every instance of Chat is listening on port 8068. You can only have one ServerSocket listening on a particular port, though it is free to accept() multiple connections. If you paid attention to the exceptions you’re getting instead of ignoring them, you would see an exception informing you of this.
Second, since the start() method of Thread returns immediately rather than waiting for the thread to finish, your while loop is creating hundreds, if not thousands, of threads. The only reason your system isn’t overwhelmed by them is because, as I mentioned above, all but the very first instance are immediately failing to bind their ServerSockets, so they return fairly quickly.
In summary, you need to create one server, with one ServerSocket. You will need to call accept() inside a loop, but you must not create more than one ServerSocket.

Ping function returns that all pinged IP addresses is reachable

I am tring to ping IP addresses from 192.168.1.1 to 192.168.1.254. First I was using I InetAddress class but it was bugged and some IPs where not reachable even if they are. After that I tried this method and it worked very well for single ping IP but when I put it inside for-loop all pinged IPs where reachable... Can you guys tell me what's wrong here?
CODE:
public class Main {
public static void main(String[] args) {
String ip="192.168.1.";
try
{
for(int i=0;i<=254;i++){
String ip2=ip+i;
boolean reachable = (java.lang.Runtime.getRuntime().exec("ping -n 1 "+ip2).waitFor()==0);
if(reachable){
System.out.println("IP is reachable:: "+ip2);
}
else{
System.out.println("IP is not reachable: "+ip2);
}
}
}catch(Exception e)
{
e.printStackTrace();
}
}
}
EDIT 1:
I used built in Java function to preform pinging but it's not working (again)
here is code that I used
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
public class Test {
public static void main(String[] args) throws UnknownHostException, IOException {
String ip = "192.168.1.243";
InetAddress inet = InetAddress.getByName(ip);
System.out.println("Sending Ping Request to " + ip);
if (inet.isReachable(5000)){
System.out.println(ip+" is reachable");
}
else{
System.out.println(ip+" is not reachable");
}
}
}
OUTPUT IS:
Sending Ping Request to 192.168.1.243
192.168.1.243 is not reachable
Also here is ping result when I do pinging from Windows 7 built in Ping function (cmd)

Use isReachable() instead.
InetAddress.getByName(address).isReachable(timeout);

Why it does not work:
You are using the exit status of the ping process, not the actual result of the ping itself. It will just tell you whether or not the process exited normally or not. A failed ping does not cause the process to exit abnormally, and thus an exit code of 0 (zero) is always returned.
What you could try instead:
Get the output stream of the process, which will tell you what the output is. Then try to interpret/parse this however you would like:
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Process.html#getOutputStream%28%29
(Although this also doesn't feel perfect for me, it is a much better choice than using the exit code)

Dear sir The issue why you program cannot ping systems over the loop is, the execution of the loop is faster compared to the replies from the systems.That is why some of them replies Unreachable, in order to solve such problem you are supposed to use a thread and introduce a little delay on each ping by using Thread.sleep() method.I think this will work Thank you

Run server and client application coding with java

Thank everyone to see my problem.
I'd like to explain my problem on Socket with java.
Using socket ,one for server to waiting for connection from client, the other for client to connect with server. THERE ARE TWO PROBLEM~~
(1)
+++After they all connect with each other, the two side can exchange messages to each other. I'have already finished the two Application code with server and client with each own main THREAD,but I can't let them communicate with each other. I use windows command to run this two file .class. I run server first ,and then I run client. They can't communicate with each other. I Want to know whether this is a problem about congestion.If I establish a another thread ,this problem could be solved??
(2) I attempt to run this two application on two eclipse,in other words each eclipse run one application. Why this problem can be solved??
(3)HERE is my code for client:
import java.util.*;
import java.io.*;
import java.net.*;
public class CC {
public static void main(String args[]){
Socket client=null;
DataInputStream in=null;
DataOutputStream out=null;
try{
client=new Socket("127.0.0.1",2060);
in=new DataInputStream(client.getInputStream());
out=new DataOutputStream(client.getOutputStream());
System.out.println("You are a client,you send message to server");
Scanner cin=new Scanner(System.in);
while(true){
String send=null,receive=null;
System.out.println("Please input Client message sending to server!");
send=cin.nextLine();
out.writeUTF(send);
receive=in.readUTF();
System.out.println("Message from Server is:"+receive);
Thread.sleep(500);
}
}
catch(Exception e){
System.out.println("break！"+e);
}
}
}
Here is my code for server
import java.util.*;
import java.io.*;
import java.net.*;
public class SS {
public static void main(String args[]){
ServerSocket socketServer=null;
DataInputStream in=null;
DataOutputStream out=null;
Socket server;
try{
socketServer=new ServerSocket(2060);
}
catch(Exception e1){
System.out.println("can't estblish socketServer "+e1);
}
try{
Scanner cin=new Scanner(System.in);
System.out.println("you are server ,please send message to client");
server=socketServer.accept();
in=new DataInputStream(server.getInputStream());
out=new DataOutputStream(server.getOutputStream());
while(true){
String send=null,receive=null;
receive=in.readUTF();
System.out.println("get message from client is "+receive);
System.out.println("send message from client");
send=cin.nextLine();
out.writeUTF(send);
}
}
catch(Exception e){
System.out.println("break！ "+e);
}
}
}

The server and client code deadlocks.
In the client code you have written send=cin.nextLine();, which blocks until more input is available. In the server code you have written receive=in.readUTF(); which too blocks until input is available.
That is, immediately after a connection is established, both the server and the client expects the other to send something which results in a deadlock and both of them wait indefinitely.
You have to make sure that either the server or the client first sends some output before waiting to accept input.

thank you,I have solve this problem under my friends.Because I have run this application before,the port has been occupied.Then I run this application for the second time,this result these two application can not transfer message. These two Application is totally right.

Why do I get permission denied connecting to port 338?

I was given this sample code from college today and it worked fine inside the college but when I run it (using Eclipse) on my home machine I get permission denied. The machine in college is Windows (7) and my computer at home is Linux (Ubuntu).
Why am I getting the following error?
Error in I/O
Permission denied
I'm using port 338.
Copy of the code :
import java.io.*;
import java.net.*;
import java.util.*;
public class Server
{
public static void main(String[] args)
{
try
{
// First create the input from the keyboard
BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Server Program");
// Get the port to listen on
System.out.print("Enter port number to listen on: ");
String port_string = input.readLine();
// The port number needs to be an int, so convert the String to an int
int port = Integer.parseInt(port_string);
// Create a ServerSocket to listen on this address
ServerSocket server = new ServerSocket(port);
// Accept an incoming client connection on the server socket
Socket sock = server.accept();
// Create the output stream to the client
DataOutputStream network = new DataOutputStream(sock.getOutputStream());
// Send message
network.writeUTF("Welcome " + sock.getInetAddress().getHostName() + ". We are " + new Date() + "\n");
// Close sockets. This will cause the client to exit
sock.close();
server.close();
}
catch (IOException ioe)
{
System.err.println("Error in I/O");
System.err.println(ioe.getMessage());
System.exit(-1);
}
}
}

Ports under 1024 are on most modern OS's (Ubuntu included) privileged, and require you to run the program as administrator/root or with elevated privileges.
Try a higher port for testing at home and you should be ok.

You say your home machine is running Ubuntu.
On Ubuntu (and other Unix-like operating systems) normal users are not allowed to listen on ports less than port 1024.
Try running it with a port number >= 1024.

Using sockets with PHP and Java

I attempted to create a PHP script which determines if the server (the computer which hosts the java program listed below) is running or not, If it is, the php funciton should return true, if not it returns false.
Here is the server:
package darestium.minecraft.server;
import java.io.BufferedReader;
import java.net.*;
import java.io.*;
public class Server {
private static ServerSocket socket;
private static Socket connection;
private static String command = new String();
private static String responseStr = new String();;
private static int port = 4343;
public static void main(String args[]) {
System.out.println("Signal Server is running.");
try {
socket = new ServerSocket(port);
while (true) {
connection = socket.accept();
InputStreamReader inputStream = new InputStreamReader(connection.getInputStream());
DataOutputStream response = new DataOutputStream(connection.getOutputStream());
BufferedReader input = new BufferedReader(inputStream);
command = input.readLine();
response.writeBytes(responseStr);
response.flush();
//response.close();
System.out.println("Running");
}
} catch (IOException e) {
System.out.println("Fail!: " + e.toString());
}
System.out.println("Closing...");
}
}
And here is the client:
<?
function isRunning() {
$address = 'darestium.dyndns-free.com';
$port = 4343;
$socket = socket_create(AF_INET, SOCK_STREAM, getprotobyname('tcp'));
$message = 'loolololol';
try {
socket_connect($socket, $address, $port);
$status = socket_sendto($socket, $message, strlen($message), MSG_EOF, $address, $port);
if ($status != false) {
return true;
}
return false;
} catch (Exception $e) {
return false;
}
}
?>
The following are the error messages that show up on the php page that echos out the result of the function like so:
include('server.php');
echo isRunning();
Then the error messages:
Warning: socket_connect() [function.socket-connect]: unable to connect [0]: No connection could be made because the target machine actively refused it. in C:\Users\darestium\Documents\Portables\xampp\htdocs\darestium\minecraftserver.php on line 9
Notice: Use of undefined constant MSG_EOF - assumed 'MSG_EOF' in C:\Users\darestium\Documents\Portables\xampp\htdocs\darestium\minecraftserver.php on line 11
Warning: socket_sendto() expects parameter 4 to be long, string given in C:\Users\darestium\Documents\Portables\xampp\htdocs\darestium\minecraftserver.php on line 11
I was wondering how I could fix this issue. Also, I would like to be able to send messages to the server, any ideas how I could do this? I am basing this off Simple Java TCP Server and PHP Client Problems
Note: that I am very new to Sockets, and Server/Client communication.
Edit:
#VideanuAdrian OK, just port forwarded the port 4343 and it no longer shows up with the first error, but the function always seems to return false, and the last two errors still show.

You should not close the DataOutputStream object in your server.
Just comment the line response.close(); in your server and the program should work.

When running a Client/Server you need to know if the user that runs the app has access to the port. Ports to 1024 are reserved by the system know apps/services. That´s point 1.
Point 2: One of the best ways is to run the server inside a connection-thread approach. Running in this way, when a new client request arrives, the server can delegate the request handle to the connection thread.
Point 3: The message is related to the protocol. If you are using a built protocol like HTTP or FTP, you must use the protocol rules. If not, you could built your own rules for the message request/response.
I recomend you to read the Java Networking Tutorial before continue. Run all Java examples. Later, you could mix with PHP. The more information about sockets and protocols you have, the better your programm will be.
http://docs.oracle.com/javase/tutorial/networking/
Hope this can help you.