We Keep Coding

Getting error in client-server programming

I have created client Server program in java. While I run program I should get port number and IP address but I am getting an error while I run Client.java. Below is my both files.
Server.java
package serverpro;
import java.io.*;
import static java.lang.ProcessBuilder.Redirect.to;
import java.net.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Server extends Thread {
public static final int PORT_NUMBER = 12345;
protected Socket socket;
public static void main(String[] args) {
ServerSocket server = null;
try {
server = new ServerSocket(PORT_NUMBER);
while (true) {
new Server(server.accept());
}
}
catch(IOException ex) {
System.out.println("Unable to start server or acccept connections ");
System.exit(1);
}
finally {
try {
server.close();
}
catch(IOException ex) {
// not much can be done: log the error
// exits since this is the end of main
}
}
}
private Server(Socket socket) {
this.socket = socket;
start();
}
// the server services client requests in the run method
public void run() {
InputStream in = null;
OutputStream out = null;
BufferedReader inReader = new BufferedReader(newInputStreamReader(in));
// the constructor argument “true” enables auto-flushing
PrintWriter outWriter = new PrintWriter(out, true);
outWriter.println("Echo server: enter bye to exit.");
//outWriter.println(“Echo server: enter ‘bye’ to exit.”);
while (true) {
// readLine blocks until a line-terminated string is available
String inLine;
try {
inLine = inReader.readLine();
} catch (IOException ex) {
Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
}
// readLine returns null if the client just presses <return>
try {
in = socket.getInputStream();
out = socket.getOutputStream();
// ... do useful stuff ...
}
catch(IOException ex) {
System.out.println("Unable to get Stream from ");
}
finally {
try {
in.close();
out.close();
socket.close();
}
catch(IOException ex) {
// not much can be done: log the error
}
}
}
}
}
Client.java
package serverpro;
import java.io.*;
import java.net.*;
public class Client {
public static void main(String args[]) throws IOException {
new Client(args[0]);
}
public Client(String host) throws IOException {
Socket socket;
try {
socket = new Socket(host, Server.PORT_NUMBER);
}
catch(UnknownHostException ex) {
System.out.println(host + " is not a valid host name.");
return;
}
catch(IOException ex) {
System.out.println("Error connecting with" + host);
return;
}
// … initialize model, GUI, etc. ...
InputStream in = null;
OutputStream out = null;
try {
in = socket.getInputStream();
out = socket.getOutputStream();
// ... do useful stuff ...
}
finally {
try {
in.close();
out.close();
socket.close();
}
catch(IOException ex) {
// not much can be done ...
}
}
}
}
Here is the error code I am getting while running client.java file
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at serverpro.Client.main(Client.java:13)
/Users/Puja Dudhat/Library/Caches/NetBeans/8.2/executor- snippets/run.xml:53: Java returned: 1
BUILD FAILED (total time: 0 seconds)

Your code expects one argument passed into the main method, which appears to be your client port, stored at args[0]. Therefore, you have to provide one to the main method. An example for setting port=12345:
java Server 12345
If you'd need more arguments, (e.g. a value at args[1]), then simply add another argument when launching main:
java Server 12345 secondArg

Assuming you are not passing required command-line argument. When I ran this code it did run fine, provided the argument required is passed or hard-coded; namely:
public static void main(**String args[]**) throws IOException {
new Client(**args[0]**);
}

if you are running both server and client on same machine then you can pass localhost as command line argument
java Client localhost
Alternatively, you can hard code host value(note : this is not good practice though),
public static void main(String args[]) throws IOException {
new Client("localhost");
}
Also as a suggestion, you can use ide like eclipse or intellij to debug your code step by step. you can go through online video tutorials for java and many are available on youtube

Java - ServerSocket error

I'm attempting to receive a message from another computer, with a simple chat client.
I'm getting this error in the Console:
Starting Listener.......
Could not listen on that port
error: null
I get this in the Console when I send text over.
Here's my code
import java.io.*;
import java.net.*;
class TCPServer
{
public static void main(String argv[]) throws Exception
{
System.out.println("Starting Listener.......");
try{
ServerSocket welcomeSocket = new ServerSocket(5060);
while(true)
{
//
// Read a message sent by client application
//
Socket clientSocket = welcomeSocket.accept();
ObjectInputStream ois = new ObjectInputStream(clientSocket.getInputStream());
String message = (String) ois.readObject();
System.out.println("Message Received: " + message);
}
}
catch (IOException e) {
System.out.println("Could not listen on that port");
System.out.println("error: "+e.getMessage());
System.exit(-1);
}
}
}
Can anyone see what I'm doing that's causing that null value? For that matter, what's causing the catch exception when I send a text string over.

Use System.out.println("error: "+e) to see the exception type which should provide more detail on what exactly went wrong - Java's class library exceptions are notorious for not including a message detailing the problem (and have only started getting better about this in recent releases).
Also, your catch of IOException will include any errors using the socket, including your attempt to read from a listen socket, so your error handling is misleading and insufficient.

Trying to get a java socket program to work, but getting "java.net.BindException: Address already in use 6666 "

Here is the code
I have written a server and client. But when i run them, (as you can see in the last program), I get the following error:
Whoop s! java.net.BindException: Address already in use 6666
6666 is the port no. i specified.
import java.net.*;
import java.io.*;
import java.lang.*;
public class processSendHelper
{
Process p;
String address;
int port;
long msg_data;
processSendHelper(int pid, int current_round, long address, long msg_data, int port)
{
try
{
ServerSocket sSoc = new ServerSocket(port);
Socket inSoc = sSoc.accept();
msg_Thread msgT = new msg_Thread(inSoc, msg_data);
msgT.start();
Thread.sleep(5000);
sSoc.close();
}
catch(Exception e)
{
System.out.println("Whoop s! " + e.toString());
}
}
}
/* sends out (or rather just makes available) the provided msg
* */
class msg_Thread extends Thread
{
Socket threadSoc;
long msg_data;
msg_Thread (Socket inSoc, long msg_data)
{
threadSoc = inSoc;
this.msg_data = msg_data;
}
public void run()
{
try
{
PrintStream SocOut = new
PrintStream(threadSoc.getOutputStream());
SocOut.println(msg_data);
}
catch (Exception e)
{
System.out.println("Whoops!" + e.toString());
}
try
{
threadSoc.close();
}
catch (Exception e)
{
System.out.println("Oh no! " +
e.toString());
}
}
}
import java.net.*;
import java.io.*;
public class processReceiveHelper
{
Socket appSoc;
BufferedReader in;
String message;
String host;
int port;
processReceiveHelper(String host,int port)
{
try
{
appSoc = new Socket(host,port);
in = new BufferedReader(new InputStreamReader(appSoc.getInputStream()));
message = in.readLine();
System.out.println(message);
/* Tokenizer code comes here
* Alongwith the code for
* updating the process object's
* data
* */
}
catch (Exception e)
{
System.out.println("Died... " +
e.toString());
}
}
}
public class Orchestrator
{
public static void main(String[] args)
{
processSendHelper psh = new processSendHelper(1, 2, 1237644, 6666, 2002);
processReceiveHelper prh = new processReceiveHelper("localhost", 2002);
}
}
EDIT:
I found the problem. The reason was that i was running both the server and client from the same main program.
the following worked:

That means there is already an application operating on port 6666 preventing your Java application using it. However, it is equally possible there is a running process of your Java application still holding onto 6666. Terminate any running java processes and try re-running the code - if it still fails then you have some other application using 6666 and you would be better using a different port.

That means that the port 6666 is already being used. There are two main causes/solutions for this:
Some other program is using that port. Solution: Choose a different port.
Your old Java program is hanging and still "using" that port. Close all of your hanging Java programs and try again. If that doesn't solve your problem, choose a different port.

Does it happen when you run the program for the second time? You may want to setReuseAddress(true) on this socket.

Listen to port via a Java socket

A server software my client communicates with regularly sends transaction messages on port 4000. I need to print those messages to the console line by line. (Eventually I will have to write those values to a table, but I’m saving that for later.)
I tried this code but it doesn’t output anything:
package merchanttransaction;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.ClassNotFoundException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
public class MerchantTransaction {
public static void main(String[] args) {
try {
InetAddress host = InetAddress.getLocalHost();
Socket socket = new Socket("192.168.1.104", 4000);
ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
String message = (String) ois.readObject();
System.out.println("Message: " + message);
ois.close();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
By the way, I need to be able to monitor that port until the program terminates. I’m not sure if the code above will be able to do that because I don’t see any iteration to the code.
I’m using Java version 1.6.0_24, SE Runtime Environment (build 1.6.0_24-b07) running on Ubuntu.

You need to use a ServerSocket. You can find an explanation here.

What do you actually want to achieve? What your code does is it tries to connect to a server located at 192.168.1.104:4000. Is this the address of a server that sends the messages (because this looks like a client-side code)? If I run fake server locally:
$ nc -l 4000
...and change socket address to localhost:4000, it will work and try to read something from nc-created server.
What you probably want is to create a ServerSocket and listen on it:
ServerSocket serverSocket = new ServerSocket(4000);
Socket socket = serverSocket.accept();
The second line will block until some other piece of software connects to your machine on port 4000. Then you can read from the returned socket. Look at this tutorial, this is actually a very broad topic (threading, protocols...)

Try this piece of code, rather than ObjectInputStream.
BufferedReader in = new BufferedReader (new InputStreamReader (socket.getInputStream ()));
while (true)
{
String cominginText = "";
try
{
cominginText = in.readLine ();
System.out.println (cominginText);
}
catch (IOException e)
{
//error ("System: " + "Connection to server lost!");
System.exit (1);
break;
}
}

Help me to fix a bug in this thread example

I am trying to create a thread to simply send the text to client. However, if you copy this code to IDE, you will see that there is a red underline under client.getOutputStream(). I do not know what is wrong here. The IDE says "Unhandled exception type IOException". Could anybody tell me?
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
public class ServerStudentThread extends Thread {
Socket client;
public ServerStudentThread(Socket x) {
client = x;
}
public void run() {
// create object to send information to client
PrintWriter out = new PrintWriter(client.getOutputStream(),true);
out.println("Student name: ");//send text to client;
}
}
For reference, here is the code that calls the thread.
import java.io.*;
import java.net.*;
import java.util.*;
public class Server2 {
public static void main(String args[]) throws Exception {
int PORT = 5555; // Open port 5555
//open socket to listen
ServerSocket server = new ServerSocket(PORT);
Socket client = null;
while (true) {
System.out.println("Waiting for client...");
// open client socket to accept connection
client = server.accept();
System.out.println(client.getInetAddress()+" contacted ");
System.out.println("Creating thread to serve request");
ServerStudentThread student = new ServerStudentThread(client);
student.start();
}
}
}

It's probably that getOutputStream() can throw an exception and you're not catching it, try putting a try / catch (IOException e) around the block of code.
public void run() {
try {
// create object to send information to client
PrintWriter out = new PrintWriter(client.getOutputStream(),true);
out.println("Student name: ");//send text to client;
} catch (IOException e) {
throw new RuntimeException("It all went horribly wrong!", e);
}
}

So you need to add a try/catch block to handle the I/O exception.
Read the section on Exceptions from the Java tutorial.

From the javadoc:
public OutputStream getOutputStream() throws IOException
IOException is a checked exception. You need to use a try/catch block to handle that possibility.

Kalla,
You need to either put the line in between try/catch block or declare run to throw IOException