Java socket readLine() 方法异常行为

Question

I have the following code snippet in a socket server for testing.

try (BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
    PrintWriter out = new PrintWriter(client.getOutputStream(), true)){

    String input;
    while ((input = in.readLine()) != null) {
        if (input.equalsIgnoreCase("exit")) {
            System.out.println("Received `exit`... closing client " + client.getRemoteSocketAddress());
            break;
        }

        System.out.println("Received: " + input);
        out.println("OK");
    }
} catch(IOException e) {
    e.printStackTrace();
}

When i send a line to it with white space eg Hello World , it only prints Hello . It seems that readLine() method behaves like the line is terminated when reading white space.

Is it a character encoding issue or what? Any help would be much appreciated.

Answer 1

In the comments, you mentioned how you send the data:

Scanner keyboard = new Scanner(System.in);
out.println(keyboard.next());

And indeed the Scanner.next() call returns each word separately, as described in the documentation :

A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace .

Naively, you might expect that you'd see Hello on the server immediately after you type the space. That doesn't happen because the input stream is line-buffered by default, so the Scanner doesn't see any input until you press Enter.

To read input line by line, you don't need a Scanner ; simply wrap System.in in a BufferedReader and use its readLine() method.