Am writing a Server, client chat program using Java Socket. Here is my code for the Server socket class.
import java.io.*;
import java.net.*;
public class Main {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(8085);
} catch (IOException ex) {
System.out.println("IO Error, " + ex);
System.exit(1);
}
Socket clientSocket = null;
System.out.println("Listening for incoming connections");
try {
clientSocket = serverSocket.accept();
} catch (IOException ex) {
System.out.println("Failed to accept connection " + ex);
System.exit(1);
}
System.out.println("Connection Successful");
System.out.println("Listening to get input");
PrintStream output = new PrintStream(clientSocket.getOutputStream(), true);
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String inputLine;
while ((inputLine = input.readLine()) != null) {
System.out.println(inputLine);
System.out.println("Server: ");
inputLine = input.readLine();
output.println(inputLine);
if (!inputLine.equals("exit")) {
} else {
break;
}
}
output.close();
input.close();
clientSocket.close();
serverSocket.close();
}
}
The client is able to make a connection and send a message to the server. The server can also receive the messages sent by the client. The problem is that when the message is sent from the server, the client does not receive the message. Here is my client socket code.
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.net.Socket;
public class Client {
public static void main(String [] args) throws Exception
{
BufferedReader input;
PrintStream output;
BufferedReader clientInput;
try (Socket client = new Socket("127.0.0.1", 8085)) {
input = new BufferedReader(new InputStreamReader(client.getInputStream()));
output = new PrintStream(client.getOutputStream());
clientInput = new BufferedReader(new InputStreamReader(System.in));
String line;
while(true)
{
System.out.println("Client: ");
line = clientInput.readLine();
output.println("Server: " + line );
if(line.equals("quit"))
{
break;
}
}
}
input.close();
clientInput.close();
output.close();
}
}
Server side:
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(8085);
} catch (IOException ex) {
System.out.println("IO Error, " + ex);
System.exit(1);
}
Socket clientSocket = null;
System.out.println("Listening for incoming connections");
try {
clientSocket = serverSocket.accept();
} catch (IOException ex) {
System.out.println("Failed to accept connection " + ex);
System.exit(1);
}
System.out.println("Connection Successful");
System.out.println("Listening to get input");
PrintStream output = new PrintStream(clientSocket.getOutputStream(), true);
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String inputLine;
while ((inputLine = input.readLine()) != null) {
System.out.println("Client request: " + inputLine);
String resp = "some response as you need";
output.println(resp);
System.out.println("Server response: " + resp);
if (!inputLine.equals("exit")) {
} else {
break;
}
}
output.close();
input.close();
clientSocket.close();
serverSocket.close();
}
}
Client side:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.net.Socket;
public class Client {
public static void main(String[] args) throws Exception {
BufferedReader input;
PrintStream output;
BufferedReader clientInput;
try (Socket client = new Socket("127.0.0.1", 8085)) {
input = new BufferedReader(new InputStreamReader(client.getInputStream()));
output = new PrintStream(client.getOutputStream());
clientInput = new BufferedReader(new InputStreamReader(System.in));
while (true) {
String inputStr = clientInput.readLine();
output.println(inputStr);
System.out.println("Client: " + inputStr);
if (inputStr.equals("quit")) {
break;
}
String serverResp = input.readLine();
output.println("Server: " + serverResp);
}
}
}
}
It is tested.
It's always a good idea to flush your output streams when you are done with them, the info you are sending may have buffered.
The server is expecting an extra line from the client input here:
while ((inputLine = input.readLine()) != null) {
System.out.println(inputLine);
System.out.println("Server: ");
inputLine = input.readLine(); // <--- here
The client is not reading from the InputStream called input it gets when it connects to the server. It is only reading the local console input from clientInput.
In the while loop in Client.java you need something like this after the quit block to get the server's response:
System.out.println("Server: " + input.readLine());
Related
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I'm trying to create a program where a client and server send text messages to each other (in utf-8 string format) similar to how two phones text message each other. Eventually I will need to create four lines (two to encode/decode utf-8 string on server side) (two to encode/decode utf-8 string on client side) This program uses two threads, one for the client one for the server.
Screenshot of error in mac terminal (command prompt)
There were no errors before I changed the following lines of code:
String MessageFromClientEncodedUTF8 = "";
BufferedReader BufReader1 = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String MessageFromClientDecodedFromUTF8 = BufReader1.readLine();
System.out.println("The message is currently encoded UTF-8");
byte[] bytes = MessageFromClientEncodedUTF8.getBytes("UTF-8");
String MessageFromClientDecodedUTF8 = new String(bytes, "UTF-8");
System.out.println("Message received from client (decoded utf-8): "+ MessageFromClientDecodedUTF8);
There are three files: the main function file, the server file, and the client file. When the main function file runs, if the "-l" command line argument is present, the server file will run, otherwise the client will run.
Server file (DirectMessengerServer.java):
import java.io.*;
import java.net.*;
import java.util.*;
import static java.nio.charset.StandardCharsets.*;
public class DirectMessengerServer
{
private static Socket socket;
boolean KeepRunning = true;
void ServerRun(String[] args)
{
Thread Server = new Thread ()
{
public void run ()
{
System.out.println("Server thread is now running");
try
{
System.out.println("Try block begins..");
int port_number1= Integer.valueOf(args[1]);
System.out.println("Port number is: " + port_number1);
ServerSocket serverSocket = new ServerSocket(port_number1);
//SocketAddress addr = new InetSocketAddress(address, port_number1);
System.out.println( "Listening for connections on port: " + ( port_number1 ) );
while(KeepRunning)
{
//Reading the message from the client
String MessageFromClientEncodedUTF8 = "";
BufferedReader BufReader1 = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String MessageFromClientDecodedFromUTF8 = BufReader1.readLine();
System.out.println("The message is currently encoded UTF-8");
byte[] bytes = MessageFromClientEncodedUTF8.getBytes("UTF-8");
String MessageFromClientDecodedUTF8 = new String(bytes, "UTF-8");
System.out.println("Message received from client (decoded utf-8): "+ MessageFromClientDecodedUTF8);
//Shut down with zero-length message
if(MessageFromClientDecodedFromUTF8.equals(""))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8.equals(null))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8=="")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8==null)
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8=="\n")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
//creating message to server send from standard input
String newmessage = "";
try {
// input the message from standard input
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
String line = "";
System.out.println( "Standard input (press enter then control D when finished): " );
while( (line= input.readLine()) != null && KeepRunning==true )
{
newmessage += line + " \n ";
}
}
catch ( Exception e ) {
System.out.println( e.getMessage() );
}
//Writing return message back to client
String returnMessage = newmessage;
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write(returnMessage + "\n");
System.out.println("Message sent to client: "+returnMessage);
bw.flush();
}
}
catch ( Exception e )
{
e.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
};
Server.start();
}
}
Client file (DirectMessengerClient.java):
import java.io.*;
import java.net.*;
import java.util.*;
import static java.nio.charset.StandardCharsets.*;
public class DirectMessengerClient
{
boolean KeepRunning = true;
private static Socket socket;
//static String[] arguments;
//public static void main(String[] args)
//{
// arguments = args;
//}
public DirectMessengerClient()
{
//System.out.println("test.");
}
public void ClientRun(String[] args)
{
Thread Client = new Thread ()
{
public void run()
{
System.out.println("Client thread is now running");
try
{
System.out.println("Try block begins..");
String port_number1= args[0];
System.out.println("Port number is: " + port_number1);
int port = Integer.valueOf(port_number1);
System.out.println("Listening for connections..");
System.out.println( "Listening on port: " + port_number1 );
while(KeepRunning)
{
String host = "localhost";
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);
//Send the message to the server
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
//creating message to send from standard input
String newmessage = "";
try
{
// input the message from standard input
BufferedReader input= new BufferedReader(
new InputStreamReader(System.in));
String line = "";
System.out.println( "Standard input (press enter then control D when finished): " );
while( (line= input.readLine()) != null )
{
newmessage += line + " ";
}
}
catch ( Exception e )
{
System.out.println( e.getMessage() );
}
String sendMessage = newmessage;
bw.write(sendMessage + "\n"); // <--- ADD THIS LINE
bw.flush();
System.out.println("Message sent to server: "+sendMessage);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String MessageFromServer = br.readLine();
System.out.println("Message received from server: " + MessageFromServer);
if(MessageFromServer.equals(""))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer.equals(null))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer=="")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer==null)
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer=="\n")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
}
}
catch ( Exception e )
{
e.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
};
Client.start();
}
}
Main function file (DirectMessengerCombined.java):
public class DirectMessengerCombined
{
public static void main(String[] args)
{
DirectMessengerClient Client1 = new DirectMessengerClient();
DirectMessengerServer Server1 = new DirectMessengerServer();
for (int i = 0; i < args.length; i++)
{
if(!args[0].equals("-l"))
{
Client1.ClientRun(args);
}
switch (args[0].charAt(0))
{
case '-':
if(args[0].equals("-l"))
{
Server1.ServerRun(args);
}
}
i=args.length + 20;
}
}
}
My question is: How do I change the way the strings are encoded or decoded in order to send strings to the other side or how to solve the null pointer exception error?
It is because you are trying to get the inputstream of a socket before it exists:-
BufferedReader BufReader1 = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
socket = serverSocket.accept();
These two lines should be the other way around. :)
EDIT: Looking further at your code, you are creating BufReader1 (which is causing the error) and then creating br in exactly the same way, i.e. both are a BufferedReader of the socket. You only need one; having two will probably cause problems for the readers.
Apologies as I asked something similar last night, but I have narrowed my problem down. I am wondering how to make my Java TCP Socket Server read in the data sent using the printWriter(out) in the Client code from a GUI as it does from the command line stdin.
I have the following classes as an example and everything works fine until the GUI comes into the equation. The data is being sent over to the Server from the GUI as I can echo it on the server side, but it is not being read and parsed properly as the stdin is. Nothing is being sent back to the client. I have tried flushing, using different streams and adding line separators all over the place to no avail. There is also a Protocol class that handles the data on the Server side.
public class KnockKnockServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(4444);
System.out.println("Waiting for client...");
} catch (IOException e) {
System.err.println("Could not listen on port: 4444.");
System.exit(1);
}
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
} catch (IOException e) {
System.err.println("Accept failed.");
System.exit(1);
}
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String inputLine, outputLine;
KnockKnockProtocol kkp = new KnockKnockProtocol();
outputLine = kkp.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
System.out.println(inputLine);
outputLine = kkp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye.")) {
break;
}
}
out.close();
in.close();
clientSocket.close();
serverSocket.close();
}
}
.
public class KnockKnockClient {
public static PrintWriter out = null;
public static String sendAnswer;
public static void Client() {
//JButton Action Listener
saveAnswer.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
ButtonModel b = group.getSelection();
if (b.getActionCommand() == "A") { sendAnswer = radioA.getText(); }
String data = "รท" + sendAnswer;
out.println(data);
}
});
}
public static void main(String[] args) throws IOException {
KnockKnockClient.Client();
Socket kkSocket = null;
//PrintWriter out = null;
BufferedReader in = null;
try {
kkSocket = new Socket("localhost", 4444);
out = new PrintWriter(kkSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(kkSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: localhost.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: localhost.");
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromServer, fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("Bye."))
break;
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
out.close();
in.close();
stdIn.close();
kkSocket.close();
}
}
I am writing a client-server program in java using TCP/IP. For the purpose, I wrote the following codes:
serversock.java:
import java.net.*;
import java.io.*;
public class serversock {
public static void main(String[] args) throws IOException
{
ServerSocket sersock = null;
try
{
sersock = new ServerSocket(10007);
}
catch (IOException e)
{
System.out.println("Can't listen to port 10007");
System.exit(1);
}
Socket clientSocket = null;
System.out.println("Waiting for connection....");
try
{
clientSocket = sersock.accept();
}
catch ( IOException ie)
{
System.out.println("Accept failed..");
System.exit(1);
}
System.out.println("Conncetion is established successfully..");
System.out.println("Waiting for input from client...");
PrintWriter output = new PrintWriter(clientSocket.getOutputStream());
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String inputLine = input.readLine();
while ( inputLine != null)
{
output.println(inputLine);
System.out.println("Server: " + inputLine);
inputLine = input.readLine();
}
input.close();
clientSocket.close();
sersock.close();
}
}
clientsock.java:
import java.util.*;
import java.io.*;
import java.net.*;
public class clientsock
{
public static void main(String[] args) throws IOException
{
Socket sock = new Socket("localhost",10007);
// Scanner scan = new Scanner(System.in);
PrintWriter output = new PrintWriter(sock.getOutputStream(),true);
BufferedReader input = new BufferedReader( new InputStreamReader(sock.getInputStream()));
String line = null;
BufferedReader stdInput = new BufferedReader( new InputStreamReader(System.in));
System.out.println("Enter data to send to server: ");
line = stdInput.readLine();
while ( (line) != "bye")
{
output.println(line.getBytes());
line = stdInput.readLine();
System.out.println("Server sends: " + input.read());
}
sock.close();
}
}
Now on running the programs I got the following output:
server:
shahjahan#shahjahan-AOD270:~/Documents/java$ java serversock
Waiting for connection....
Conncetion is established successfully..
Waiting for input from client...
Server: [B#4e25154f
shahjahan#shahjahan-AOD270:~/Documents/java$
client:
shahjahan#shahjahan-AOD270:~/Documents/java$ java clientsock
Enter data to send to server:
qwe
sdf
^Cshahjahan#shahjahan-AOD270:~/Documents/java$
The server is recieving different symbols, and client receives nothing. Please help me to solve it.
In the client replace:
output.println(line.getBytes());
with
output.println(line);
I am using Socket and ServerSocket classes to communicate on local host
client sends a no. to server and server computes square of no. and sends back to the client
// Client Class
import java.net.*;
import java.io.*;
class SocketDemo
{
public static void main(String...arga) throws Exception
{
Socket s = null;
PrintWriter pw = null;
BufferedReader br = null;
System.out.println("Enter a number one digit");
int i=(System.in.read()-48); // will read only one character
System.out.println("Input number is "+i);
try
{
s = new Socket("127.0.0.1",10101);
pw = new PrintWriter(s.getOutputStream());
br = new BufferedReader(new InputStreamReader(s.getInputStream()));
System.out.println("Connection established, streams created");
}
catch(Exception e)
{
System.out.println("Exception in Client "+e);
}
pw.println(i);
System.out.println("Data sent to server");
String str = br.readLine();
System.out.println("The square of "+i+" is "+str);
}
}
// Server Side
import java.io.*;
import java.net.*;
class ServerSocketDemo
{
public static void main(String...args)
{
ServerSocket ss=null;
PrintWriter pw = null;
BufferedReader br = null;
int i=0;
try
{
ss = new ServerSocket(10101);
}
catch(Exception e)
{
System.out.println("Exception in Server while creating connection"+e);
}
System.out.print("Server is ready");
while (true)
{
System.out.println (" Waiting for connection....");
Socket s=null;
try
{
s = ss.accept();
System.out.println("Connection established with client");
pw = new PrintWriter(s.getOutputStream());
br = new BufferedReader(new InputStreamReader(s.getInputStream()));
i = new Integer(br.readLine());
System.out.println("i is "+i);
}
catch(Exception e)
{
System.out.println("Exception in Server "+e);
}
System.out.println("Connection established with "+s);
i*=i;
pw.println(i);
try
{
pw.close();
br.close();
}
catch(Exception e)
{
System.out.println("Exception while closing streams");
}
}
}
}
Please Help
On client side do this after sending data to server
pw.println(i);
pw.flush();
I have a problem when the client send data to the server. When I send data from the server to the client everything is okay. I received this message: "client receive: message" but then when I send "client's message", my server do not receive it.
import java.io.IOException;
import java.net.*;
import java.io.*;
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(4444);
} catch (IOException e) {
System.err.println("Could not listen on port: 4444.");
System.exit(1);
}
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
} catch (IOException e) {
System.err.println("Accept failed.");
System.exit(1);
}
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(
clientSocket.getInputStream()));
String inputLine, outputLine;
outputLine = "message";
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
System.out.println("server receive: " + inputLine);
outputLine = "second message";
out.println(outputLine);
}
out.close();
in.close();
clientSocket.close();
serverSocket.close();
}
}
public void actionPerformed(ActionEvent e) {
if (e.getSource() == startButton) {
this.main.getContentPane().remove(homePanel);
String name = this.name.getText();
String result;
try {
connectionToServer();
if ((result = in.readLine()) != null) {
System.out.println("client receive: " + result);
out.println("client's message");
}
} catch(IOException err) {
System.out.println("error");
}
}
}
public void connectionToServer() throws IOException {
try {
this.socket = new Socket("localhost", 4444);
this.in = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
this.out = new PrintWriter(this.socket.getOutputStream(), true);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: taranis.");
System.exit(1);
}
}
your actionPerformed method just link the server and do nothing.
The server closed after send a message.
watch: while ((inputLine = in.readLine()) != null)
if client don't send any message,code will break,then you closed the server.