Android Java-发送一个时的两个套接字消息

Question

I send a message over sockets from an android app to a java program. This message is sent with a printwriter.

here is how I send my message from android to java program:

out.println("Hello there");
out.flush();

This is how I receive the message:

while(true){
String msg = in.readLine();

System.out.println("MSG: " + msg);

...some if-statements...
}

The output of the System.out.println is: MSG: Hello there * MSG: null *

How come I get null there? I'm only sending "hello there"..

Help would be appreciated, thanks!

EDIT: Actual code of the java program.

while (run) {
            String msg = in.readLine();
            String[] parts;  
            String username;
            String password = null;

            System.out.println("MSG: " + msg);

            parts = msg.split("\\*");
            username = parts[0];
            password = parts[1];

            boolean validUser = false;

            validUser = db.authenticate(username, password);

            if (validUser) {
                        db.updateIP(username,                     socket.getInetAddress().getHostAddress());
                        out.println("done");
                        out.flush();
            } else {
                        out.println("loginfail");
                        out.flush();
                        closeSocketConnection();
                }
            }
        }

    private void closeSocketConnection() throws IOException {
        in.close();
        out.close();
        socket.close();
        run = false;
    }

Answer 1

What is your exit condition for your while loop?

It looks to me like it is repeating and readLine will return null when the end of the stream has been reached causing MSG: null to be printed.

Updated given new information:

Assuming user*123 is a valid username/password combo then closeSocketConnection() is never called, the loop returns to the top, readLine returns null and you see your erroneous output. Followed by a NullPointerException on parts = msg.split("\\\\*");

Answer 2

Your loop should read:

while ((line = in.readLine()) != null)
{
    // ...
}

At the moment you're processing the null that indicates end of stream inside the loop, hence you're printing it as a message when it isn't.