I have a socket client sending text to a socket server but the ReadLine doesnt seem to wait to receive a line before proceeding. Here is the of the server receiving the text:
public void run() {
try {
serveurSocket = new ServerSocket(PORT_ID);
connexionSocket = serveurSocket.accept();
BufferedReader reader = new BufferedReader(new InputStreamReader(connexionSocket.getInputStream()));
PrintWriter writer = new PrintWriter(connexionSocket.getOutputStream(), true);
messageRecu = "";
while (true) {
messageRecu = reader.readLine();
messageRecu = messageRecu.toUpperCase();
writer.println(messageRecu);
}
//reader.close();
//writer.close();
} catch (IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
After establishing the socket between client and server, the execution halts at reader.readLine until I send manually a string thru the socket. Which is normal and wanted. Codes resumes and its fine until its loops back to reader.ReadLine() where it will read a "null" line instead of waiting for input from the socket like it did the first time... this will obviously mess up the next command to uppercase. So how can I fix this?
EDIT: I'll add the client side if that can help understand.
public class ClientSocket {
private Socket clientSocket;
public boolean isClosed() { return clientSocket.isClosed(); }
public boolean connectToSocket (String ip, int port) {
try {
clientSocket = new Socket(ip, port);
return true;
}
catch (IOException e) {
System.out.println(e);
return false;
}
}
public String sendToServer(String messageClient) {
String messageRecu = "";
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
PrintWriter writer = new PrintWriter(clientSocket.getOutputStream(), true);
writer.println(messageClient);
messageRecu = reader.readLine();
reader.close();
writer.close();
return messageRecu;
}
catch (IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
return messageRecu;
}
}
}
A button press will call "connectTosocket" to initiate the socket. A second button when pressed will send the content of a textfield using "sendToServer".
Server does receive the message and return it capitalized but I wish for the socket to remain open with the server and if I send an other string for the same sequence to happen. Not even sure it can be done :(
According to the documentation of BufferedReader#readLine
, a null is returned if the end of stream has been reached.
Change your reading loop to :
while ((messageRecu = reader.readLine()) != null) {
messageRecu = messageRecu.toUpperCase();
writer.println(messageRecu);
}
//Get out of the loop when the end of stream is reached.
As per Reading from and Writing to a Socket chapter of the Java tutorial.
As a side note, while(true)
loops are not really appreciated .
The "null" signals for end of connection from the client side - which is why the connection disconnects. If you want to support multiple requests, you should run a new ServerSocket.accept()
each time and wait for a new client to connect.
import java.net.*;
import java.io.*;
public class KKMultiServer {
public static void main(String[] args) throws IOException {
if (args.length != 1) {
System.err.println("Usage: java KKMultiServer <port number>");
System.exit(1);
}
int portNumber = Integer.parseInt(args[0]);
boolean listening = true;
try (ServerSocket serverSocket = new ServerSocket(portNumber)) {
while (listening) {
new KKMultiServerThread(serverSocket.accept()).start();
}
} catch (IOException e) {
System.err.println("Could not listen on port " + portNumber);
System.exit(-1);
}
}
}
import java.net.*;
import java.io.*;
public class KKMultiServerThread extends Thread {
private Socket socket = null;
public KKMultiServerThread(Socket socket) {
super("KKMultiServerThread");
this.socket = socket;
}
public void run() {
try (
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
) {
String inputLine, outputLine;
KnockKnockProtocol kkp = new KnockKnockProtocol();
outputLine = kkp.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = kkp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye"))
break;
}
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
You can read more about sockets in Oracle tutorials
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