使用servlet发送邮件时，在netBeans中显示未知主机异常

Question

有我的档案：

的index.html

<form action="servlet/SendMail">
To:<input type="text" name="to"/><br/>
Subject:<input type="text" name="subject"><br/>
Text:<textarea rows="10" cols="70" name="msg"></textarea><br/>
<input type="submit" value="send">
</form>

SendMail.java

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class SendMail extends javax.servlet.http.HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        String to=request.getParameter("to");

        String subject=request.getParameter("subject");

        String msg=request.getParameter("msg");

        Mailer.send(to, subject, msg);


        out.print("message has been sent successfully");
        out.close();
    }

}

Mailer.java

import java.util.Properties;

import javax.mail.*;

import javax.mail.internet.InternetAddress;

import javax.mail.internet.MimeMessage;

public class Mailer {
public static void send(String to,String subject,String msg){

final String user="myid@gmail.com";

final String pass="*********";

Properties props = new Properties();

  props.setProperty("mail.smtp.port", "465");

    props.put("mail.transport.protocol", "smtp");

        props.setProperty("mail.smtp.socketFactory.port", "465");

        props.put("mail.smtp.socketFactory.class", 
"javax.net.ssl.SSLSocketFactory");
        props.setProperty("mail.smtp.host", "smtp.gmail.com");

        props.setProperty("mail.smtp.starttls.enable", "true");

        props.setProperty("mail.smtp.auth", "true");


Session session = Session.getInstance(props,

 new javax.mail.Authenticator() {

  protected PasswordAuthentication getPasswordAuthentication() {

   return new PasswordAuthentication(user,pass);

   }
});

try {
 MimeMessage message = new MimeMessage(session);

 message.setFrom(new InternetAddress(user));

 message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));

 message.setSubject(subject);

 message.setText(msg);

 Transport.send(message);

 System.out.println("Done");

 } catch (MessagingException e) {

    throw new RuntimeException(e);
 }

}
}