java - 如何在没有客户端提示的情况下接收从服务器到客户端的消息

Question

所以我正在制作一个基本的聊天应用程序。这是来自客户端的代码片段。这里我向服务器发送信息，然后得到回复。

但是，有时服务器会向客户端发送消息，而不需要客户端先向服务器发送信息。我该如何实现这个？

while (true){    
        String sentence;
        BufferedReader inFromUser =
            new BufferedReader(new InputStreamReader(System.in));
        sentence = inFromUser.readLine();

        // send to server
        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
        outToServer.writeBytes("\n");

        // create read stream and receive from server
        BufferedReader FromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        System.out.println(FromServer.readLine());


    }

例如，服务器可能会以随机间隔向我发送随机信息。但只有当我先向服务器发送一些东西时我才能收到它们。但如果我实现类似的东西(如下所示)，我将不再能够向服务器发送信息，只能充当接收者。但我希望能够在必要时发送信息和接收信息，而不必先发送某些内容。

while (true){    

        // receive from server only
        BufferedReader FromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        System.out.println(FromServer.readLine());


    }

我在回复第一条评论时更改了什么。我遵循了你的代码，所以这就是我所做的。但是，我似乎仍然无法自发地接收消息，即我仍然需要按 Enter 或键入输入来接收随机发送的任何服务器信息:

BufferedReader FromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    while (true) {  
        // Check if there's anything to receive
        while (FromServer.ready()) {
            // receive from server
            System.out.println(FromServer.readLine());
        }

        String sentence;
        BufferedReader inFromUser =
        new BufferedReader(new InputStreamReader(System.in));
        sentence = inFromUser.readLine();

        // write to server
        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
        outToServer.writeBytes(sentence + '\n');

// Send data to the server here if required.
    }

Answer 1

将其更改为这样的内容:-

BufferedReader FromServer = 
    new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromUser =
    new BufferedReader(new InputStreamReader(System.in));

while (true) {  
    // Check if there's anything to receive
    while (FromServer.ready()) {
        // receive from server
        System.out.println(FromServer.readLine());
    }
    if (inFromUser.ready()) {
        int ch = inFromUser.read();

        // write to server
        outToServer.writeChar(ch);
    }


}

现在客户端将读取任何要读取的内容，并且可以在需要时发送数据。