BufferedReader readLine 方法挂起并阻塞程序 [英] BufferedReader readLine method hangs and block program

问题描述

我正在尝试使用 Java 学习套接字，并且我成功地将数据发送到在我自己的机器上运行的 ServerSocket.当我尝试使用 readline 从这个套接字读取时(所以我可以只回显我自己发送的消息)我的程序挂起并且不会返回.

I'm trying to learn sockets using Java and I sucessfully sent data to a ServerSocket running in my own machine. When I try to read from this socket using readline (so I can just echo my own sent message) my program hangs and won't return.

代码如下:

public static void main(String[] args) throws UnknownHostException, IOException {

    TCPClient cli = new TCPClient("127.0.0.1", "15000");
    try {
        cli.ostream.writeUTF("Teste");
        String echo = cli.istream.readLine(); //it hangs in this line
        System.out.println(echo);
    }

TCPClient 是我定义的一个类，因此我可以在我的工作中使用 Swing 之前在更简单的界面上测试我的程序.这是代码:

TCPClient is a class I defined so I can test my program on a simpler interface before using swing on my homwework. here's the code:

public class TCPClient {

public DataOutputStream ostream = null;
public BufferedReader istream = null;

public TCPClient(String host, String port) throws UnknownHostException {
    InetAddress ip = InetAddress.getByName(host);

    try {
        Socket socket = new Socket(host, Integer.parseInt(port));

        ostream = new DataOutputStream(socket.getOutputStream());
        istream = new BufferedReader(new InputStreamReader(socket.getInputStream()));


    } catch (IOException ex) {
        Logger.getLogger(TCPClient.class.getName()).log(Level.SEVERE, null, ex);
    }

}

我的服务器很简单.连接建立后，它进入这个循环并一直停留在这里直到我关闭客户端(因为无限循环).之后，一些异常处理将其返回到连接开始之前的点.

My server is pretty simple. After the connection is estabilished, it enters in this loop and stays here until I close the client (because of the infinite loop). Afterwards, some exception handling returns it to the point before the connection started.

            while(true){
                String msg = istream.readLine();
                System.out.println("Arrived on server: " + msg); //just works on debug
                ostream.writeUTF("ACK: " + msg);
                ostream.flush();
            }

我不知道我错过了什么.

I don't see what am I missing.

PS:奇怪的是，如果我调试服务器，我可以看到到达那里的消息(例如，我可以打印它)，但是如果我只运行此代码，这是不可能的.这是否有一些我忽略的并发关系?

PS: the wierd stuff is that if I debug the server, I can see the message arriving there (I can print it, for example), but this isn't possible if I just run this code. Does this have some concurrency relation I'm overlooking?

谢谢

推荐答案

问题在于 readLine 尝试读取一行.在确定到达行尾之前，它不会返回该行.这意味着它需要换行符或通信结束.由于服务器不发送任何换行符并且不关闭流，因此客户端无限期地等待.

The problem is that readLine tries reading a line. It will not return the line until it's sure that the end of line has been reached. This means that it expects either a newline character, or the end of the communication. Since the server doesn't send any newline char and doesn't close the stream, the client waits indefinitely.

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