Java 套接字 - 读和写

Question

问题:客户端没有收到任何消息。

这是客户端和服务器的完整代码:

客户

public class Client extends Socket{


public Client(String hostName, int port) throws UnknownHostException, IOException {
    super(hostName,port);

    BufferedReader in = new BufferedReader(new InputStreamReader(getInputStream()));

    while(true) {
        String line = in.readLine();
        System.out.println("Text received: " + line);
    }

}

服务器

public final class Server extends ServerSocket{

public Server(int port) throws IOException {
    super(port);

    System.out.println("Server waiting for client 1");
    Socket client1 = accept();
    PrintWriter writer = new PrintWriter(client1.getOutputStream(), true);
    writer.write("Hello user 1");

    System.out.println("Server waiting for client 2");
    Socket client2 = accept();
    PrintWriter writer2 = new PrintWriter(client2.getOutputStream(), true);
    writer2.write("Hello user 2");

    System.out.println("Clients connected");

}

• 我启动服务器来监听端口 4444
• 我使用主机名“localhost”和端口 4444 启动客户端

Answer 1

您必须在消息末尾包含一个换行符，如果连接没有立即更改，还必须刷新 PrintWriter，强制自动刷新:

writer.write("Hello user 1\n");
writer.flush();

编辑:

可以使用构造函数在 PrintWriter 上启用自动刷新new PrintWriter(someOutputStream, true)

但是，正如文档中所解释的:

if automatic flushing is enabled it will be done only when one of the println, printf, or format methods is invoked, rather than whenever a newline character happens to be output

这意味着即使使用自动刷新，在调用 write 后仍需要手动刷新 PrintWriter，并且换行符 (\n) 仍将具有包含在字符串的末尾。

编辑2:

这是一个功能齐全的客户端/服务器应用程序的小示例:

客户:

public static void main(String[] args){
    try{
        Socket socket = new Socket(HOST_ADDRESS, PORT);
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        System.out.println(bufferedReader.readLine());
        bufferedReader.close();
        socket.close();
    }catch(IOException e){}
}

服务器:

public static void main(String[] args){
    try{
        ServerSocket serverSocket = new ServerSocket(PORT);
        Socket socket = serverSocket.accept();
        PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
        printWriter.write("Hello user!\n");
        printWriter.flush();
        printWriter.close();
        socket.close();
        serverSocket.close();
    }catch(IOException e){}
}