BufferedReader.readLine（）暂停我的应用程序？

Question

I am using this code:

while (true) {
    sendData("hi");
    System.out.println("Data sent!");
    BufferedReader inFromServer;
    try {
        inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    } catch (IOException e1) {
        inFromServer = null;
        e1.printStackTrace();
    }
    System.out.println("Recieved!"); //I see this de-bug message.
    try {
        modifiedSentence = inFromServer.readLine();
        System.out.println("FROM SERVER: " + modifiedSentence); //I do NOT see this de-bug message!
    } catch (IOException e) {
        e.printStackTrace();
    }
}

It successfully sends data to a server - And the server successfully sends data back:

public void run () {
    //handle the session using the socket (example)
    try {
        sendData("Hi");
        System.out.println("Data sent!"); //I see this de-bug message.
    } catch (Exception e) {
        e.printStackTrace();
    }
}

However for some reason, the application seems to pause at the inFromServer.readLine() method. I see the "Recieved!" de-bug message, but not the "FROM SERVER" de-bug message.

There are no errors at all. It just seems to hang there.

Why is it hanging, and how can I fix that?

Answer 1

Well this simply means that inFromServer does not receive any line.

Make sure you really send a line,

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\\n'), a carriage return ('\\r'), or a carriage return followed immediately by a linefeed.

Have a look at the readLine method :

String readLine(boolean ignoreLF) throws IOException {
    StringBuffer s = null;
    int startChar;

    synchronized (lock) {
        ensureOpen();
        boolean omitLF = ignoreLF || skipLF;

    bufferLoop:
        for (;;) {

            if (nextChar >= nChars)
                fill();
            if (nextChar >= nChars) { /* EOF */
                if (s != null && s.length() > 0)
                    return s.toString();
                else
                    return null;
            }
            boolean eol = false;
            char c = 0;
            int i;

            /* Skip a leftover '\n', if necessary */
            if (omitLF && (cb[nextChar] == '\n'))
                nextChar++;
            skipLF = false;
            omitLF = false;

        charLoop:
            for (i = nextChar; i < nChars; i++) {
                c = cb[i];
                if ((c == '\n') || (c == '\r')) {
                    eol = true;
                    break charLoop;
                }
            }

            startChar = nextChar;
            nextChar = i;

            if (eol) {
                String str;
                if (s == null) {
                    str = new String(cb, startChar, i - startChar);
                } else {
                    s.append(cb, startChar, i - startChar);
                    str = s.toString();
                }
                nextChar++;
                if (c == '\r') {
                    skipLF = true;
                }
                return str;
            }

            if (s == null)
                s = new StringBuffer(defaultExpectedLineLength);
            s.append(cb, startChar, i - startChar);
        }
    }
}

Note that this one receive a boolean, but calling readLine simply call this one with false passed, unless on Linux.

Notice the for(;;) loop, which is an infinite loop.

Try concatening to the "line" sent from the server

System.getProperty("line.separator");