使用 Java 发送电子邮件，连接到 gmail 主机挂起

Question

我想通过 Java 代码发送电子邮件。我在我的库中添加了以下 .JAR：log4j.jar、smtp.jar、mailapi.jar、ctivation.jar。我的 Java 类看起来像这样：

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;

public class SendEmail
{
public static void main(String [] args)
{    
   String to = "abcd@gmail.com";
   String from = "web@gmail.com";
   String host = "smtp.gmail.com";
   Properties properties = System.getProperties();


   properties.setProperty("mail.smtp.host", host);
   properties.setProperty("mail.smtp.starttls.enable", "true");
   properties.setProperty("mail.smtp.auth", "true");

   SmtpAuthenticator authentication = new SmtpAuthenticator();
   javax.mail.Message msg = new MimeMessage(Session
                       .getInstance(properties, authentication));

   try {
       msg.setFrom(new InternetAddress(from));
       msg.setRecipient(Message.RecipientType.TO, 
           new InternetAddress(to));
       msg.setSubject("Subject");
       msg.setText("Working fine..!");
       System.out.println("fine1    !!");
       Transport transport = Session.getDefaultInstance( properties , null).getTransport("smtp");
       System.out.println("fine2    !!");
       transport.connect("smtp.gmail.com" , 465 , "username", "password");
       System.out.println("fine3    !!");
       Transport.send(msg);
       System.out.println("fine!!");
   }
   catch(Exception exc) {
       System.out.println(exc);
   }
}
}

我的 SmtpAuthenticator 类：

import javax.mail.Authenticator;
import javax.mail.PasswordAuthentication;

public class SmtpAuthenticator extends Authenticator {
    public SmtpAuthenticator() {

        super();
    }

    @Override
    public PasswordAuthentication getPasswordAuthentication() {
        String username = "user";
        String password = "password";
        if ((username != null) && (username.length() > 0) && (password != null)
                && (password.length() > 0)) {

            return new PasswordAuthentication(username, password);
        }

        return null;
    }
}

当我运行我的 Java 应用程序类时，它会打印： 很好1！ 很好2！！

然后挂起。我怎样才能摆脱这个问题？

Answer 1

问题出在这一行：

transport.connect("smtp.gmail.com" , 465 , "username", "password");

465 是 smtp over ssl (smtps) 的端口，所以要么使用端口 25：

transport.connect("smtp.gmail.com" , 25 , "username", "password");

或改为使用 smtps

Transport transport = Session.getDefaultInstance( properties , null).getTransport("smtps");

transport.connect("smtp.gmail.com" , 465, "username", "password");