Java 从套接字读取时获取空字符串_Java_Sockets_Client Server

Java 从套接字读取时获取空字符串

java sockets

Java 从套接字读取时获取空字符串,java,sockets,client-server,Java,Sockets,Client Server,我试图用java编写一个使用套接字的客户机-服务器系统，但是我似乎无法读取从服务器发送到客户机的数据以下是客户端的代码： public class ClientSocket { Socket clientSocket = null; PrintWriter out = null; BufferedReader in = null; // establish a connection to All Care's server application thro

我试图用java编写一个使用套接字的客户机-服务器系统，但是我似乎无法读取从服务器发送到客户机的数据

以下是客户端的代码：

public class ClientSocket 
{
    Socket clientSocket = null;
    PrintWriter out = null;
    BufferedReader in = null;


    // establish a connection to All Care's server application through socket 4444 (adjust localhost to reflect the IP address that the server
    // is being run from)
    public ClientSocket()
    {
        try
        {
            clientSocket = new Socket("localhost", 4445);

            out = new PrintWriter(clientSocket.getOutputStream());
            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        }
        catch (IOException e)
        {
            System.out.println("Could not connect to All Care Server Application");
        }
    }

    public void closeClientSocket()
    {   
        try
        {
            clientSocket.close();
        }
        catch (IOException e)
        {
            System.out.println("Could not close connection to All Care Server Application");
        }
    }

    public String getMessageFromServer()
    {
        try
        {
            String input = in.readLine();

            return input;
        }
        catch (IOException e)
        {
            System.out.println("Could not read message from server");
        }

        return "No Data";
    }

    public void sendMessageToServer(String message)
    {
        out.write(message);
    }
}

以下是服务器代码：

public class ArFileServer {

    public static void main(String[] args) 
    {
        ServerSocket serverSocket = null;
        boolean listening = true;

        try
        {
            serverSocket = new ServerSocket(4445);

            // infinite loop to continually listen for connection requests made by clients
            while (listening)
            {
                new ClientConnection(serverSocket.accept()).start();

                if (serverSocket != null)
                {
                    System.out.println("Connection to client established");
                }
            }

            serverSocket.close();
        }
        catch (IOException e)
        {
            System.out.println("Error could not create socket connection to port");
        }
    }
}

public class ClientConnection extends Thread
{
    private Socket socket = null;

    public ClientConnection(Socket socket) 
    {
        super("ClientConnection");
        this.socket = socket; 
    }

    // the thread that runs after a connection to the server has been accepted
    @Override
    public void run()
    {
        try
        {
            PrintWriter out = new PrintWriter(socket.getOutputStream());
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            sendMessagetoClient(out, "CONNECTION SUCCESS");

            // check login credentials sent from client to the server

            // if valid send back their encrypted password, otherwise output a login error message

            // wait for user input and then do various processes based on their requests

            in.close();
            out.close();
            socket.close();
        }
        catch (IOException e)
        {
            System.out.println("Client socket connection error");
        }
    }

    // sends a message to the client
    void sendMessagetoClient(PrintWriter out, String message)
    {
        out.write(message);
    } 

    // listens for a message from the client
    String getMessageFromClient(BufferedReader in)
    {      
        try
        {
            String input = in.readLine();
            return input;
        }
        catch (IOException e)
        {
            System.out.println("Could not read message from client");
        }

        return "No Data";
    }

这是我用来查看数据是否被发送的代码行

System.out.println(clientSocket.getMessageFromServer());

在clint代码中，您没有连接到服务器套接字。用于clint插座连接

在

sendMessageToClient（）

方法中，需要刷新：

void sendMessagetoClient(PrintWriter out, String message)
{
    out.write(message);
    out.flush();
}

或者，当您创建

PrintWriter

时，将构造函数与

autoflush

一起使用：

PrintWriter out = new PrintWriter(socket.getOutputStream(),true);

当你写的时候，不要写出来。写（消息）使用

printf（）

或

println（）

在你的

sendMessageToClient（）方法中，你需要刷新：
void sendMessagetoClient(PrintWriter out, String message)
{
    out.write(message);
    out.flush();
} 


或者，当您创建PrintWriter
时，将构造函数与autoflush
一起使用：
PrintWriter out = new PrintWriter(socket.getOutputStream(),true);

当你写的时候，不要写出来。写（消息）

使用

printf（）

或

println（）

这里有几个问题

你在读台词，但不是在写台词

您没有检查readLine（）的结果是否为null，这意味着对等方已经关闭了连接，这意味着您必须执行同样的操作

在编写之后，您没有刷新

PrintWriter

你把事情按错误的顺序结束了。必须关闭连接到套接字的输出写入程序/流。这样做会刷新它，然后关闭输入流/读取器和套接字。按错误的顺序操作会失去冲水功能。关闭输出后，不需要关闭其他两个

您使用的是

PrintWriter，

，它通过网络接收异常，您需要了解通信中的异常和错误，并且也不检查错误。使用

BufferedWriter.