Java程序 - IP地址ping和发送电子邮件程序

Question

相对较新的编程。我正在尝试编写一个ping IP地址的程序。当主机在线时它什么都不做，但在离线时它会向收件人发送一封电子邮件。然而，它每次都会发送电子邮件 - 在线和离线！我知道我很亲密，任何帮助都会很棒！代码片段......

    final String username = "[email protected]";
    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 OFFLINE\n");

    try {


        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("[email protected]"));
        message.setRecipients(Message.RecipientType.TO,
            InternetAddress.parse("[email protected]"));
        message.setSubject("Project Test Mail");
        message.setText("Test Mail,"
            + "\n\n Sent From sendMail.java application");

        Transport.send(message);

        System.out.println("Mail Sent to [email protected] " 
         +     ipAddress);

    } catch (MessagingException e) {
        throw new RuntimeException(e);
    }
} 

Answer 1

您的消息部分不在您的else语句范围内。如果不对if / else / for / etc使用大括号，则只考虑下一行。把它放在{}

        final String username = "[email protected]";
        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 OFFLINE\n");

        try {


            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress("[email protected]"));
            message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse("[email protected]"));
            message.setSubject("Project Test Mail");
            message.setText("Test Mail,"
                + "\n\n Sent From sendMail.java application");

            Transport.send(message);

            System.out.println("Mail Sent to [email protected] " 
             +     ipAddress);

        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    } 
}

Answer 2

您的try块与if语句无关。 java中的一个好习惯总是使用if / else块的花括号，如果不使用花括号，则只会执行关于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。

并在此代码中：

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

doSometingElse（）仅在someTest（）为true时执行