java - Python 客户端 Java 服务器 服务器接收到 null

Question

顾名思义，客户端向服务器发送空值。我想不通为什么

Python 客户端

import socket

HOST = "localhost"
PORT = 5000

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((HOST, PORT))

dict = {
    0: "doug",
    1: "korg",
    2: "stefan",

}
for x in range(0, 3):
    if x == 3:
        sock.sendall("Bye\n")
        print(sock.recv(1024))
    sock.sendall(b"{}\n".format(dict.get(x)))
    print(dict.get(x))
    print(sock.recv(1024))

Java 服务器:

    public void run() {
        String fromClient;
        String toClient;
        try {
            ServerSocket server = new ServerSocket(5000);
            System.out.println("wait for connection on port 5000");

            boolean run = true;
            Socket client = server.accept();

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


            while (run) {
                System.out.println("got connection on port 5000");
                fromClient = in.readLine();
                System.out.println("received: " + fromClient);


                if (fromClient.equals("Bye")) {
                    toClient = "Aight later man";
                    System.out.println("send eyB");
                    out.println(toClient);
                    client.close();
                    System.out.println("socket closed");
                    break;
                }
                out.println("cool next User Please");
            }
            System.exit(0);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

当前 3 个字符串从客户端发送到服务器并且服务器响应时，当发送 Bye 时，服务器接收到 null 并抛出 nullpointerexception。

我的代码基于这篇文章。 Communication between python client and java server

问题存在于 String as ByteString 形式。

服务器输出:

wait for connection on port 5000
got connection on port 5000
received: doug
got connection on port 5000
received: korg
got connection on port 5000
received: stefan
got connection on port 5000
Exception in thread "Thread-0" java.lang.NullPointerException
    at Jserver.run(Jserver.java:28)
received: null

Process finished with exit code 0

客户端输出:

doug
cool next User Please

korg
cool next User Please

stefan
cool next User Please

Answer 1

您的问题是由 python 代码引起的，它从不发送“再见”命令。

python代码中的错误:

您的 python 代码从 0(含)循环到 3(不含)，因为 3 被排除在外，代码永远不会进入“再见” block ，也永远不会发送它。 (打印 x 以确认这一点)

在循环之后放置“bye”代码。

for x in range(0, 3):
    sock.sendall(b"{}\n".format(dict.get(x)))
    print(dict.get(x))
    print(sock.recv(1024))
sock.sendall("Bye\n")
print(sock.recv(1024))

Java代码中的错误

是的，Java 代码中也有一个错误，主要是它没有正确处理流关闭。

当 Python 程序在代码末尾关闭时，Java 程序将收到一个干净的退出，这是一种无异常的关闭套接字的方式，并将导致 readLine返回空值。

此 null 然后导致以下异常:

Exception in thread "Thread-0" java.lang.NullPointerException

由于看到 null 值意味着套接字已关闭，您还可以将其作为适当的“再见”响应或作为错误条件进行线程处理。

            if (fromClient == null || fromClient.equals("Bye")) {