Java 程序 - IP 地址 ping 并发送电子邮件程序

Question

相对新手编程。我正在尝试编写一个pingIP地址的程序。当主机联机时，它不执行任何操作，但在脱机时，它会向收件人发送电子邮件。但是，它每次都会发送电子邮件 - 在线和离线！我知道我已经很接近了，任何帮助都会很棒！代码片段...

    final String username = "[e-mail]";
    final String password = "Password";    
    Properties props = new Properties();
    props.put("mail.smtp.auth", "true");
    props.put("mail.smtp.starttls.enable", "true");
    props.put("mail.smtp.host", "smtp.gmail.com");
    props.put("mail.smtp.port", "587");
    Session session = Session.getInstance(props,
            new javax.mail.Authenticator() {
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(username, password);
                }
            });    

    InetAddress i = InetAddress.getByName(ipAddress);
    System.out.println("Sending Ping Request to " + ipAddress);
    if (i.isReachable(5000)) //5 second limit
        System.out.println("Host is online n");
    else
        System.out.println("HOST IS OFFLINEn");
    try {

        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("[e-mail]"));
        message.setRecipients(Message.RecipientType.TO,
            InternetAddress.parse("[e-mail]"));
        message.setSubject("Project Test Mail");
        message.setText("Test Mail,"
            + "nn Sent From sendMail.java application");
        Transport.send(message);
        System.out.println("Mail Sent to [e-mail] " 
         +     ipAddress);
    } catch (MessagingException e) {
        throw new RuntimeException(e);
    }
} 

Answer 1

您的消息部分不在 else 语句的范围内。如果您不使用大括号表示 if/else/for/等，则只考虑下一行。只需将其放入{}

        final String username = "[e-mail]";
        final String password = "Password";    
        Properties props = new Properties();
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.starttls.enable", "true");
        props.put("mail.smtp.host", "smtp.gmail.com");
        props.put("mail.smtp.port", "587");
        Session session = Session.getInstance(props,
                new javax.mail.Authenticator() {
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(username, password);
                    }
                });    

        InetAddress i = InetAddress.getByName(ipAddress);
        System.out.println("Sending Ping Request to " + ipAddress);
        if (i.isReachable(5000)) //5 second limit
            System.out.println("Host is online n");
        else {
            System.out.println("HOST IS OFFLINEn");
        try {

            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress("[e-mail]"));
            message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse("[e-mail]"));
            message.setSubject("Project Test Mail");
            message.setText("Test Mail,"
                + "nn Sent From sendMail.java application");
            Transport.send(message);
            System.out.println("Mail Sent to [e-mail] " 
             +     ipAddress);
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    } 
}

Answer 2

您的 try 块与 if 语句无关。Java 中一个好的做法是始终对 if/else 块使用大括号，如果不使用大括号，则只会执行有关 if/else 响应的第一行代码。

例如，在以下代码中

if(someTest())
  doSomething();
  doSomethingElse();

doSomethingElse()将始终执行。

在此代码中：

if(someTest()){
  doSomething();
  doSomethingElse();
 }

doSometingElse（） 只有在 someTest（） 为 true 时才执行