Java程序，該程序通過套接字接口與郵件服務器建立TCP連接並發送電子郵件

Question

我正在編寫一個Java程序，該程序通過套接字接口與郵件服務器建立TCP連接，並發送電子郵件。 我遇到的問題是，當我在命令行上運行它時，它會在編寫“ MAIL FROM：”后停止。 我沒有收到任何錯誤，只是到那時為止。 我無法弄清楚自己在做什么錯，因此我們將不勝感激任何幫助

import java.io.*;
import java.net.*;

public class EmailSender{

public static void main(String[] args) throws Exception{

    // Establish a TCP connection with the mail server.
     Socket socket = new Socket("" + "hostname", 25);
    // Create a BufferedReader to read a line at a time.
    InputStream is = socket.getInputStream();
    InputStreamReader isr = new InputStreamReader(is);
    BufferedReader br = new BufferedReader(isr);

    // Read greeting from the server.
    String response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("220")) {
        socket.close();
        throw new Exception("220 reply not received from server.");
    }

    // Get a reference to the socket's output stream.
    OutputStream os = socket.getOutputStream();

    // Send HELO command and get server response.
    String command = "HELO alice\r\n";
    System.out.print(command);
    os.write(command.getBytes("US-ASCII"));
    response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("250")) {
        socket.close();
        throw new Exception("250 reply not received from server.");
    }

    // Send MAIL FROM command.
    String mailFrom = "MAIL FROM: <email>";
    System.out.print(mailFrom);
    os.write(mailFrom.getBytes("US-ASCII"));
    response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("250")) {
        socket.close();
        throw new Exception("250 reply not received from server.");
    }

    // Send RCPT TO command.
    String commandRCPT = "RCPT TO: <email>";
    System.out.print(commandRCPT);
    os.write(commandRCPT.getBytes("US-ASCII"));
    response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("250")) {
        socket.close();
        throw new Exception("250 reply not received from server.");
    }

    // Send DATA command.
    String commandDATA = "DATA";
    System.out.print(commandDATA);
    os.write(commandDATA.getBytes("US-ASCII"));
    response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("354")) {
        socket.close();
        throw new Exception("354 reply not received from server.");
    }

    // Send message data.
    String msgLine1 = "email sent";
    System.out.print(msgLine1);
    os.write(msgLine1.getBytes("US-ASCII"));

    // End with line with a single period.
    String msgLine2 = ".";
    System.out.print(msgLine2);
    os.write(msgLine2.getBytes("US-ASCII"));
    response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("250")) {
        socket.close();
        throw new Exception("250 reply not received from server.");
    }

    // Send QUIT command.
    String commandQUIT = "QUIT";
    System.out.print(commandQUIT);
    os.write(commandQUIT.getBytes("US-ASCII"));
    response = br.readLine();
    System.out.println(response);
    if (!response.startsWith("221")) {
        socket.close();
        throw new Exception("221 reply not received from server.");
    }

    socket.close();
}
}

Answer 1

您正在編寫"MAIL FROM: <johnstoy@uwindsor.ca>"但最后沒有換行。 請注意這與您發送的HELO命令之間的區別。

根據RFC 2821第2.4.7節：

SMTP命令以及消息數據（除非通過服務擴展進行了更改）均以“行”形式傳輸。 行由零個或多個數據字符組成，這些數據字符以ASCII字符“ CR”（十六進制值0D）結束，緊接着是ASCII字符“ LF”（十六進制值0A）。

您沒有終止命令，因此服務器仍在等待更多數據。

其余的命令也有同樣的問題，順便說一句。

（當然，除非純粹出於教育目的，否則您確實應該使用諸如JavaMail之類的郵件庫。）