Java 套接字 - 服务器响应始终为空

Question

我必须连接服务器(我无权访问服务器代码)但传输协议(protocol)(套接字)是:

(client) --> data

ack <-- (server)
data response <-- (server)

(client) --> ack

假定服务器应始终快速响应。我连接到服务器，我发送数据但响应为 NULL，如果我调试我的代码，当我捕获响应时会发生异常:“java.net.SocketException:软件导致连接中止:接收失败”

我的代码:

public static void main(String[] args){
    try{
        String order = "datahere";
        String responseServer;   
        BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));  

        Socket clientSocket = new Socket();
        InetSocketAddress sa = new InetSocketAddress("XXX.XX.XX.XX", 9300);
        clientSocket.connect(sa,500);

        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());   
        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));    
        outToServer.writeBytes(order);   
        responseServer = inFromServer.readLine();//exception if I try to debug my code   
        System.out.println("From server: " + responseServer); //responseServer is NULL
        clientSocket.close(); 

    } catch (IOException ex) {
            System.out.println("Error: "+ex);
    }

}

错了吗？有什么想法吗？

我尝试禁用防火墙并为端口 9300 添加规则，但结果是一样的。

客户在 Vb.Net 中给了我一个示例代码，它应该可以工作，我尝试用 Java 复制它。

Vb.Net 中的代码:

Dim message As String = "datahere";

 Try
     Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes(message)

     Dim client As New TcpClient(ip, port)
     Dim stream As NetworkStream = client.GetStream()
     stream.Write(data, 0, data.Length)

     data = New [Byte](2048) {}

     Dim responseData As [String] = [String].Empty
     Dim bytes As Integer = stream.Read(data, 0, data.Length)
     responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes)

     stream.Close()
     client.Close()

 Catch ex As Exception

End Try

解决方案:

Socket clientSocket = new Socket();
InetSocketAddress sa = new InetSocketAddress("XXX.XX.XX.XX", 9300);
clientSocket.connect(sa,500);

clientSocket.getOutputStream().write(order.getBytes("ASCII"));

byte[] data = new byte[2048];
int bytes = clientSocket.getInputStream().read(data, 0, data.length);
String responseData = new String(data, 0, bytes, "ASCII");
System.out.println("From server: " + responseData);

//Another way to catch the response:
//InputStreamReader in = new InputStreamReader(clientSocket.getInputStream());
//int data1 = in.read();
//while(data1 != -1) {
//   System.out.print((char) data1);
//   data1 = in.read();
//}

clientSocket.close();

Answer 1

这是用 java 翻译您的 VB 代码

public static void main(String[] args) throws IOException {
    String order = "datahere";

    // Try-with-resource statement will close your socket automatically
    try (Socket clientSocket = new Socket("XXX.XX.XX.XX", 9300)) {
        // Send to the sever the order encoded in ASCII
        clientSocket.getOutputStream().write(order.getBytes("ASCII"));
        // Sleep until we have bytes to read available
        while (clientSocket.getInputStream().available() == 0) {
            Thread.sleep(100L);
        }
        // Create the buffer of exactly the amount of bytes available without blocking
        byte[] data = new byte[clientSocket.getInputStream().available()];
        // Read the bytes from the server and put it into the buffer
        int bytes = clientSocket.getInputStream().read(data, 0, data.length);
        // Decode what has been read from the server that was encoded in ASCII
        String responseData = new String(data, 0, bytes, "ASCII");
        System.out.println("From server: " + responseData);
    }
}