英文:
How does a BufferedReader interact with a Socket? About how Sockets work
问题
我一直在按照教程学习如何在Java中构建简单的聊天应用程序。我已经基本了解了服务器和客户端如何通信的原理。到目前为止，我使用了PrintWriter来发送信息，并使用BufferedReader来接收双方的信息。但是我不明白的是为什么这不会导致错误？
Socket soc = new Socket(ipAddress, port);
BufferedReader in = new BufferedReader(new InputStreamReader(soc.getInputStream));
while (true) {
String str = in.readLine();
}
我的问题是，in.readLine()语句是否在“等待”输入？如果不是，如果使用str而它没有值，程序不应该抛出错误吗？或者一般来说，像Socket soc = serverSocket.accept();这样的Socket特定函数，或者像上面例子中读取InputStream一样，是否会“等待”任何信号？我是否漏掉了关于Socket的一些基本概念？如果有人能帮助我进一步理解这个主题，我会非常感谢。
提前感谢您的帮助，
Appa
英文:
I have been following a tutorial on how to build a simple chat application in Java. I get the basic principle of how sever and client communicate. So far I used a PrintWriter to send, and a BufferedReader to recieve information for both sides. But what I don´t get is how this does not lead to errors?
Socket soc = new Socket(ipAddress, port);
BufferedReader in = new BufferedReader( new InputStreamReader(soc.getInputStream));
while(true) {
String str = in.readLine();
}
My question would be the following. Is the in.readLine() statement "waiting" for input? If it does not, shouldn´t the program throw Errors if using the str since it has no value? Or in general terms, do Socket specific functions like Socket soc = serverSocket.accept(); or as in the example given above the reading of an InputStream "wait" for a signal whatsoever? Did I miss some essential concept about Sockets? It would be great if someone could help me understand this topic further.
Thank you in advance,
Appa
答案1
得分: 1
我的问题是这样的。
in.readLine()语句是否在等待输入？
是的，它在等待输入，因为.readLine()是一个阻塞方法。
如果不等待，如果使用字符串（str）而它又没有值，程序不应该抛出错误吗？
我无法解析这个问题 —— 这个陈述没有意义。你期望会有什么错误或异常？
或者用更通俗的话说，像
Socket soc = serverSocket.accept();这样的套接字特定函数，或者如上面给出的从输入流读取，在等待信号吗？
再次地，我担心这个问题不太清楚（至少对我来说是这样）。ServerSocket#accept() 是一个阻塞方法，会等待直到可以建立套接字连接，如果这就是你的问题。
注意，这段代码：
while (true) {
String str = in.readLine();
}
虽然有效，但可能不是特别有用，因为你会读取一个字符串然后丢弃它，没有对它进行任何操作。最好要么打印获取到的字符串，要么将它传递到一个方法中，在方法中可以以某种方式使用它。另一方面，我想如果你只想“吞掉”流以防止操作系统的缓冲区溢出，这可能是有用的。
英文:
> My question would be the following. Is the in.readLine() statement "waiting" for input?
Yes, it is "waiting for input" since .readLine() is a blocking method
> If it does not, shouldn´t the program throw Errors if using the str since it has no value?
I cannot parse this -- the statement doesn't make sense. What error / exception would you be expecting?
> Or in general terms, do Socket specific functions like Socket soc = serverSocket.accept(); or as in the example given above the reading of an InputStream "wait" for a signal whatsoever?
Again, I'm afraid that this is not too clear (at least to me). ServerSocket#accept() is a blocking method and will wait until a socket connection can be made, if that is what you are asking.
Note that thiscode:
while(true) {
String str = in.readLine();
}
while valid, would not be particularly useful, since you would be reading a String and then discarding it, doing nothing with it. Better to either print the String obtained, or pass it into a method where it can be used in some way. On the other hand, I suppose this could be useful if all you wanted to do was to "gobble" the stream to prevent the OS's buffers from overflowing.
答案2
得分: 0
是的，readLine实际上会阻塞。它会等待直到读取到回车符/换行符或套接字关闭。
英文:
Yes readLine does in fact block. It waits till you read a carriage return/line feed, or the socket closes.
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