Java Client/Server does not return UTF-8 string

Question

I tried to pass a UTF-8 String through a Java Socket.

The String contains a mix of English and Greek.

My problem is that when the message passes through the socket all Greek characters turn to "?".

I already tried to set the InputStream character set to UTF-8.

Bellow is my attempt, any help will be appreciated.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;

public class Main {
    public static void main(String[] args) {
        try {
            String msg = "This is a test - Αυτο ειναι μια δοκιμη";
            ServerSocket serverSocket = new ServerSocket(9999);

            Thread host = new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        try {
                            Socket socket = serverSocket.accept();

                            if (socket != null) {
                                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8));

                                while (true) {
                                    String line = bufferedReader.readLine();

                                    if (line != null) {
                                        System.out.println(line);
                                    } else if(bufferedReader.read() < 0) {
                                        break;
                                    }
                                }
                            }
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            });

            host.start();

            Socket socket = new Socket("127.0.0.1", 9999);
            PrintWriter printWriter = new PrintWriter(socket.getOutputStream(), true);
            printWriter.println(msg);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Edit 1

I run and build my code through IntelliJ Idea and that is where I found the problem.

But after @Ihar Sadounikau comment I updated and my JDK and tried to build and run through PowerShell but still the problem persists.

And this is my result

& 'C:\Program Files\Java\jdk-13.0.2\bin\java.exe' Main
This is a test - ??τ? ε??α? ??α δ?????

Works perfectly without any question mark. Try to recompile the class. I used Java 11 for the test, not sure it is an issue — Ihar Sadounikau
– Ihar Sadounikau, Commented Mar 8, 2020 at 22:49
javadoc of PrintWriter: "Creates a new PrintWriter from an existing OutputStream. This convenience constructor creates the necessary intermediate OutputStreamWriter, which will convert characters into bytes using the default character encoding." (assuming console can display the characters) — user85421
– user85421, Commented Mar 8, 2020 at 23:40

rzwitserloot · Accepted Answer · 2020-03-08 23:44:38Z

4

With this line: PrintWriter printWriter = new PrintWriter(socket.getOutputStream(), true); you are converting a bytestream (i.e., InputStream / OutputStream into a charstream (i.e., Reader / Writer). Anytime you do that, if you fail to specify the encoding, you get platform default, which is unlikely what you want.

You (and @IharSadounikau) are seeing different results, because the 'platform default' is switching around on you. It's one of the reasons you REALLY do not want to use it, ever. Figuring out that your code has the bug where it only works if your platform default encoding is the same as the person who developed it – is generally untestable.

Try new PrintWriter(socket.getOutputStream(), true, StandardCharsets.UTF_8).

edited Mar 8, 2020 at 23:44

answered Mar 8, 2020 at 23:34

rzwitserloot

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2 Comments

Giwrgos Gkogkas Over a year ago

OK, I updated my JDK, updated my gradle, changed all my run/builds and implemented your solution but still questions marks. Am I missing something?

rzwitserloot Over a year ago

Just print the line. A one-liner: System.out.println("Greek chars here"). Does that show the question marks? Then it's powershell which is misconfigured or incapable of printing these.

alexrnov · Accepted Answer · 2020-03-09 01:26:25Z

0

Maybe this will help:

String msgEncode = URLEncoder.encode(msg, "UTF-8");
printWriter.println(msgEncode);

And:

String line = bufferedReader.readLine();
String msgDecode = URLDecoder.decode(line, "UTF-8");

answered Mar 9, 2020 at 1:26

alexrnov

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