使用java语言实现简单的发送邮件功能，同时不能利用javax.mail组件，请编写java代码实现上述功能

好的，以下是使用Socket实现发送邮件的java代码：

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

public class SendMail {
    public static void main(String[] args) throws Exception {
        // 邮件服务器地址
        String smtpServer = "smtp.example.com";
        // 发件人邮箱地址
        String from = "sender@example.com";
        // 收件人邮箱地址
        String to = "recipient@example.com";
        // 邮件主题
        String subject = "Test Mail";
        // 邮件内容
        String body = "This is a test mail.";

        // 建立与邮件服务器的连接
        Socket socket = new Socket(smtpServer, 25);
        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8"));

        // 发送邮件
        out.println("HELO " + smtpServer);
        out.flush();
        in.readLine();

        out.println("MAIL FROM:<" + from + ">");
        out.flush();
        in.readLine();

        out.println("RCPT TO:<" + to + ">");
        out.flush();
        in.readLine();

        out.println("DATA");
        out.flush();
        in.readLine();

        out.println("From:" + from);
        out.println("To:" + to);
        out.println("Subject:" + subject);
        out.println();
        out.println(body);
        out.println(".");
        out.flush();
        in.readLine();

        out.println("QUIT");
        out.flush();

        in.close();
        out.close();
        socket.close();
    }
}

需要替换的部分：

- `smtpServer`：替换为你的邮件服务器地址；
- `from`：替换为发件人邮箱地址；
- `to`：替换为收件人邮箱地址；
- `subject`：替换为邮件主题；
- `body`：替换为邮件内容。