I am trying to send two numbers via Socket. The Server receive the numbers and I make some calculation, but when I send back to Client the result, the Client receive a number which he send it.
Where I doing wrong beceause I don't understand?
Client.java
public class Client {
private static Socket socket;
public static void main(String args[]) {
try {
String host = "localhost";
int port = 25010;
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);
String number = "2";
String number2 = "5";
String sendMessage = number + "\n";
String sendMessage2 = number2 + "\n";
bw.write(sendMessage);
bw.write(sendMessage2);
bw.flush();
System.out.println("Message sent to the server:\n" + sendMessage + sendMessage2);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " + message);
} catch (Exception exception) {
exception.printStackTrace();
} finally {
//Closing the socket
try {
socket.close();
} catch(Exception e) {
e.printStackTrace();
}
}
}
}
Server.java
public class Server {
private static Socket socket;
public static void main(String[] args) {
try {
int port = 25010;
ServerSocket serverSocket = new ServerSocket(port);
System.out.println("Server Started and listening to the port " + port);
ArrayList<String> arr = new ArrayList<String>();
//Server is running always. This is done using this while(true) loop
while(true) {
//Reading the message from the client
socket = serverSocket.accept();
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream())); // primeste mesaj de la client
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); // transmite raspuns catre client
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
String inputLine;
while ((inputLine = br.readLine()) != null) {
out.println(inputLine);
arr.add(inputLine.trim());
}
System.out.println("Message received from client is:");
for (int i = 0; i < arr.size(); i++) {
System.out.println(arr.get(i));
}
//Return message
String returnMessage = null;
try {
int numberInIntFormat = 0;
int num = 1;
for (int i = 0; i < arr.size(); i++) {
System.out.println(arr.get(i));
numberInIntFormat = Integer.parseInt(arr.get(i));
num = num * numberInIntFormat;
}
arr.clear();
returnMessage = String.valueOf(num);
} catch(NumberFormatException e) {
//Input was not a number. Sending proper message back to client.
returnMessage = "Please send a proper number\n";
}
//Sending the response back to the client.
bw.write(returnMessage);
bw.flush();
System.out.println("returnMessage = " + returnMessage);
System.out.println("Message sent to the client is "+ returnMessage);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
socket.close();
} catch(Exception e) {}
}
}
}
Your server code echoes everything it reads from the client back to the client before it does anything else with it:
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream())); // primeste mesaj de la client
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); // transmite raspuns catre client
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
String inputLine;
while ((inputLine = br.readLine()) != null) {
out.println(inputLine); // <-- HERE
arr.add(inputLine.trim());
}
It is unsurprising that the client receives what the server sent.
Try this:
Client:
public class Client {
private static Socket socket;
public static void main(String args[]) {
try {
String host = "localhost";
int port = 25010;
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);
String number = "2";
String number2 = "5";
String sendMessage = number + "\n";
String sendMessage2 = number2 + "\n";
bw.write(sendMessage);
bw.write(sendMessage2);
bw.newLine(); // You need to send a special line for say to the server: "Hey, I have done";
bw.flush();
System.out.println("Message sent to the server:\n" + sendMessage + sendMessage2);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " + message);
} catch (Exception exception) {
exception.printStackTrace();
} finally {
//Closing the socket
try {
socket.close();
} catch(Exception e) {
e.printStackTrace();
}
}
}
}
Server:
public class Server {
private static Socket socket;
public static void main(String[] args) {
try {
int port = 25010;
ServerSocket serverSocket = new ServerSocket(port);
System.out.println("Server Started and listening to the port " + port);
ArrayList<String> arr = new ArrayList<String>();
//Server is running always. This is done using this while(true) loop
while(true) {
//Reading the message from the client
socket = serverSocket.accept();
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream())); // primeste mesaj de la client
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); // transmite raspuns catre client
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
String inputLine;
while ((inputLine = br.readLine()) != null && inputLine.length() > 0) { // You need to stop loop when you get empty line
// out.println(inputLine);
arr.add(inputLine.trim());
System.out.println("Message received from client is:"+inputLine.trim());
}
System.out.println("Message received from client is:");
//Return message
String returnMessage = null;
try {
int numberInIntFormat = 0;
int num = 1;
for (int i = 0; i < arr.size(); i++) {
System.out.println(arr.get(i));
numberInIntFormat = Integer.parseInt(arr.get(i));
num = num * numberInIntFormat;
}
arr.clear();
returnMessage = String.valueOf(num);
} catch(NumberFormatException e) {
//Input was not a number. Sending proper message back to client.
returnMessage = "Please send a proper number\n";
}
//Sending the response back to the client.
bw.write(returnMessage+"\n"); // You need to add '\n' otherwise readLine never gets;
bw.flush();
System.out.println("returnMessage = " + returnMessage);
System.out.println("Message sent to the client is "+ returnMessage);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
socket.close();
} catch(Exception e) {}
}
}
}
String inputLine;
while ((inputLine = br.readLine()) != null) {
arr.add(inputLine.trim());
}
With this change, the output is:
Server:
Server Started and listening to the port 25010
Client:
Message sent to the server:
2
5
And now the Server is 'blocked' in while loop and the Client don't recive any feedback.
I found a better method:
while (br.ready() && (inputLine = br.readLine()) != null)
This tell that to read the buffer if it is something to read.
With the response from #John Bollinger, the buffer read only up to first line break, so if you try to parse a String which contains a line break, you will get out when appear the line break.
With br.ready() it will parse all the String and will get out at the end of buffer.
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.
I have made a socket in Java.
This socket connects with a server.
When I start my program, the server sends a message that my socket is connected with the AEOS.
When I try to login to the server for sending some commands, then the server responds again with: status connected to AEOS version
This is not the message that I expect, normally my server must send a "response true".
Can you help me?
Thanks.
import java.io.*;
import java.net.*;
class TCPClient {
public static void main(String argv[]) throws Exception {
while(true) {
String sentence;
String modifiedSentence;
Socket clientSocket = new Socket("127.0.0.1", 1201);
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + '\n');
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close();
}
}
}
output socket
Why don't you try to read everything that server had sent? Also, need to open a new Socket every-time? Depends on your implementation. Try this:
public static void main(String[] args) {
Socket clientSocket = null;
try {
clientSocket = new Socket("127.0.0.1", 1201);
BufferedReader inFromUser = new BufferedReader(
new InputStreamReader(System.in));
DataOutputStream outToServer = new DataOutputStream(
clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
String initialMessageFromServer = null;
while ((initialMessageFromServer = inFromServer
.readLine()) != null) {
System.out.println(initialMessageFromServer);
}
while (true) {
String sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + '\n');
StringBuilder modifiedSentence = new StringBuilder();
String responseFromServer = null;
while ((responseFromServer = inFromServer.readLine()) != null) {
modifiedSentence.append(responseFromServer);
modifiedSentence.append('\n');
}
System.out
.println("FROM SERVER: " + modifiedSentence.toString());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (clientSocket != null) {
try {
clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
I'd like to make a client that sends strings to a server occasionally, for example: when application closed it sends a message to server- sendToServer("Client[" + IP + "]Closed")
I have a problem in my code :
Server :
try{
int port = 25000;
ServerSocket serverSocket = new ServerSocket(port);
System.out.println("Server Started and listening to the port 25000");
//Server is running always. This is done using this while(true) loop
while(true)
{
//Reading the message from the client
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String received = br.readLine();
System.out.println("Message received from client is "+received);
//Multiplying the number by 2 and forming the return message
String returnMessage;
try
{
returnMessage = "You send : " + received;
}
catch(NumberFormatException e)
{
//Input was not a number. Sending proper message back to client.
returnMessage = "Please send a proper number\n";
}
//Sending the response back to the client.
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write(returnMessage);
System.out.println("Message sent to the client is "+returnMessage);
bw.flush();
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
try
{
socket.close();
}
catch(Exception e){
}
}
CLIENT :
try {
String host = IP;
int port = Port;
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);
String number = "2";
String sendMessage = number + "\n";
bw.write(sendMessage);
bw.flush();
System.out.println("Message sent to the server : "+sendMessage);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " +message);
}
catch (Exception exception)
{
exception.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
There are lot of close_wait connection, when ever a client client sends the message to the server and comes out the TCP FSM stuck in the CLOSE_WAIT STATE
This the Client code,
public class Client1
{
private static Socket socket;
public static void main(String args[])
{
try
{
String host = "localhost";
int port = 25000;
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);
String number = "2";
String sendMessage = number + "\n";
bw.write(sendMessage);
bw.flush();
System.out.println("Message sent to the server : "+sendMessage);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " +message);
}
catch (Exception exception)
{
exception.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
}
This the Server code which listen to the upcoming connection
public class Server1
{
private static Socket socket;
public static void main(String[] args)
{
try
{
int port = 25000;
ServerSocket serverSocket = new ServerSocket(port);
System.out.println("Server Started and listening to the port 25000");
//Server is running always. This is done using this while(true) loop
while(true)
{
//Reading the message from the client
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String number = br.readLine();
System.out.println("Message received from client is "+number);
//Multiplying the number by 2 and forming the return message
String returnMessage;
try
{
int numberInIntFormat = Integer.parseInt(number);
int returnValue = numberInIntFormat*2;
returnMessage = String.valueOf(returnValue) + "\n";
}
catch(NumberFormatException e)
{
//Input was not a number. Sending proper message back to client.
returnMessage = "Please send a proper number\n";
}
//Sending the response back to the client.
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write(returnMessage);
System.out.println("Message sent to the client is "+returnMessage);
bw.flush();
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
try
{
socket.close();
}
catch(Exception e){}
}
}
}
The output TCP FSM
-bash:~$ netstat -an | grep 25000
tcp4 0 0 127.0.0.1.25000 127.0.0.1.56459 CLOSE_WAIT
tcp46 0 0 *.25000 *.* LISTEN
You're closing the accepted socket in the wrong place. It needs to be inside the accept loop.
I would like to create a Java server socket application that receives a TCP packet and reads the content of it. Based on the contents of the packet it will perform several actions. I managed to get to the point where it reads some content and prints a string System.out.println(sb.toString());
But (a) not all the content is printed and (b) I am not sure how to process the content as they arrive in network order. An example would be to receive an HTTP packet and from the header to report the "Content-Length" or the "User-Agent". Any example would be appreciated.
public static void main(String[ ] args){
PrintWriter out = null;
BufferedReader in = null;
int bufferSize = 0;
try{
String message = args[0];
int count = 0;
ServerSocket connectionSocket = null;
try {
connectionSocket = new ServerSocket(4444);
System.out.println("Server started");
} catch (IOException e) {
System.err.println("Could not listen on port: 4444.");
System.exit(1);
}
Socket clientSocket = null;
try {
while(true){
count++;
clientSocket = connectionSocket.accept();
System.out.println("TCP packet received… " + count);
InputStream is = clientSocket.getInputStream();
out = new PrintWriter(clientSocket.getOutputStream());
in = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = in.readLine()) != null) {
sb.append(line + "\n");
}
System.out.println(sb.toString());
clientSocket.close();
}
} catch (IOException e) {
System.err.println("Accept failed.");
System.exit(1);
}
}
catch(Exception e){
e.printStackTrace();
}
}