使用套接字在客戶端和服務器之間進行通信

Question

好的，這是今天早些時候修訂的問題，我提供了有助於解釋該問題的代碼。 我正在從客戶端向服務器發送兩條消息。 然后，服務器接收消息並進行處理。 服務器最終嘗試將消息發送回客戶端（請注意服務器代碼“ testmessage”），這是我遇到的問題。 我不是在客戶端接收消息，還是從服務器端錯誤地發送消息。

public class ClientConnection {

String address, language, message;
int portNumber;
Socket clientSocket = null;

public ClientConnection(String lan, String mes, String add, int pn) throws IOException{
    address = add;
    portNumber = pn;
    language = lan;
    message = mes;
}
public String createAndSend() throws IOException{
    // Create and connect the socket
    Socket clientSocket = null;
    clientSocket = new Socket(address, portNumber);
    PrintWriter pw = new PrintWriter(clientSocket.getOutputStream(),true);
    BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));     

    // Send first message - Message is being correctly received
    pw.write(language+"\n"); 
    pw.flush(); 
    // Send off the data  

    // Send the second message - Message is being correctly received
    pw.write(message); 
    pw.flush();
    pw.close();
    // Send off the data

    // NOTE: Either I am not receiving the message correctly or I am not sending it from the server properly.
    String translatedMessage = br.readLine();       
    br.close();
    //Log.d("application_name",translatedMessage); Trying to check the contents begin returned from the server.
    return translatedMessage;
}

服務器代碼：

public class ServerConnection {

public static void main(String[] args) throws Exception {       
    // Delete - Using while loop to keep connection open permanently.
    boolean status = false;
    while( !status){
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(4444);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 4444.");
            System.exit(1);
        }
        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }
        // Delete - Working as of here, connection is established and program runs awaiting connection on 4444
        BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));     
        String language = br.readLine();
        String message = br.readLine();
        // Test - Works
        System.out.println(language);      
        // Test - Works
        System.out.println(message);
        // Delete - Working as of here, both messages are passed and applied. Messages are received as sent from client.
        TranslateMessage tm = new TranslateMessage();
        String translatedMessage = tm.translateMessage(language, message);

        // NOTE: This seems to be where I am going wrong, either I am not sending the message correctly or I am not receiving it correctly..
        // PrintWriter writer = new PrintWriter(new BufferedOutputStream(clientSocket.getOutputStream()));
        PrintWriter pw = new PrintWriter(clientSocket.getOutputStream(),true);
        // Send translation back 
        System.out.println(translatedMessage);
        // pw.write(translatedMessage+"\n"); 
        pw.write("Return test"); // Test message!
        pw.flush(); 
        // Send off the data 
        pw.close();
        br.close();
        clientSocket.close();
        serverSocket.close();
    }
}
}

代碼有點混亂，我可以看到一些重復的地方，我在出現問題的地方發表了評論。

謝謝你的幫助！

Answer 1

您正在使用BufferedReader.readLine（）從服務器讀取響應，但是在測試用例中，您發送的字符串未以\\ n或\\ r \\ n終止，因此它將無法獲得該行。我可以從文檔中看出...

public String readLine()
            throws IOException

Read a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

Returns:
    A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

另一個建議...

在編寫這樣的請求響應協議時，我不會依靠行尾來終止請求或響應。 通常，我會使用完全格式化的JSON字符串，或者我的首選是二進制協議，其中所有請求和響應都以二進制計數為前綴（通常為4字節，bigendian /網絡字節順序）。 然后，客戶端和服務器讀取這4個字節，然后讀取隨后的字節數。 這可以處理通常在網絡連接上發生的數據包碎片，還有助於避免惡意用戶發送永不終止的長字符串而引起的DOS攻擊。

在Java中，可以使用ByteBuffer.order（）處理雙端數字。