java - 套接字不保存列表中的值

Question

我是用 Java 进行网络开发的新手，我想创建一个简单的 Socket 服务器，它从客户端获取值并将所有值收集到 ArrayList 中。我编写了一个示例代码，但在服务器端它不收集字符串。这是我的服务器端:

服务器

public class ServerSideSocket extends Thread{
    private ServerSocket serverSocket;
    private Socket socket;
    private ArrayList<String> list = new ArrayList<String>();
    DataInputStream inData;
    DataOutputStream outData;

    public ServerSideSocket(int port) throws IOException {
        serverSocket = new ServerSocket(port);
    }

    public void run() {
        while(true) {
            try{
                System.out.println("Waiting for connection...");
                socket = serverSocket.accept();
                System.out.println("Connected!" );
                inData = new DataInputStream(socket.getInputStream());
                outData = new DataOutputStream(socket.getOutputStream());

                System.out.println(inData.readUTF());

                list.add(inData.readUTF());

                System.out.println("------------ VALUES ---------");
                for (String value: list) {
                    System.out.println(value);
                }
                System.out.println("------------ END VALUES ---------");

                outData.writeUTF("Message saved!");
                outData.flush();
            } catch (SocketException ex) {
                ex.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    inData.close();
                    outData.close();
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        int port = 9999;
        try {
            Thread t = new ServerSideSocket(port);
            t.start();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

}

和客户:

public class ClientSideSocket {
    public static void main(String[] args) {
        String serverName = "localhost";
        int port = 9999;
        String line = "";

        try {
            System.out.println("Connecting to " + serverName + " on port " + port);
            Socket client = new Socket(serverName, port);
            System.out.println("Just connected to " + client.getRemoteSocketAddress());
            OutputStream out = client.getOutputStream();
            DataOutputStream outData = new DataOutputStream(out);
            InputStream in = client.getInputStream();
            DataInputStream inData = new DataInputStream(in);

            outData.writeUTF("Simple text");
            outData.flush();
            System.out.println("Response from server: " + inData.readUTF());
            System.out.println("You can write more messages!");
            System.out.println();

            client.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

我的代码有什么问题吗？

Answer 1

发生这种情况是因为您尝试通过调用 inData.readUTF() 方法从数据流中读取两次。第一次调用成功从流中读取数据，但您没有保存结果，而是尝试执行下面的另一次读取 2 行。readUTF() 是阻塞方法，因此它等待永远不会来自同一客户端的另一部分数据。这就是为什么你的服务器永远挂起

您想要做的是读取一次并将结果存储到局部变量中:

String res = inData.readUTF();
list.add(res);