Question

当我通过命令行运行此代码时，我得到了一个感知。当我通过Eclipse IDE运行它时它运行正常，没有例外。我无法弄清楚发生了什么，但它确实在会话声明中得到了例外。

public static void sendEmail(String sendFile) {
    // Send the log file via email.
    final String username = "firstname.lastname@mycompany.com";
    final String password = "myPassword";

    // Strings that contain from, to, subject, body and file path to the attachment.
    String from = username;
    String to = username;
    String subject = "Baggage URL failures - Please check";
    String body = "FareDB Bad URL(s) Report. The following URL(s) could not be loaded...";
    String filename = sendFile;
    System.out.println("Mail header info set!");

    // Set smtp properties
    Properties properties = new Properties();
    properties.put("mail.smtp.starttls.enable", "true");
    properties.put("mail.smtp.auth", "true");
    properties.put("mail.smtp.host", "smtp.gmail.com");
    properties.put("mail.smtp.port", "587");
    System.out.println("SMTP properties set!");

    Session session = Session.getInstance(properties, null);
    System.out.println("Mail session declared!");

    try {
        MimeMessage message = new MimeMessage(session);
        message.setFrom(new InternetAddress(from));
        // Just me for testing
        message.setRecipient(Message.RecipientType.TO, new InternetAddress(username));
        message.setSubject(subject);
        message.setSentDate(new Date());
        System.out.println("Mail body info set!");

        // Set the email body
        MimeBodyPart messagePart = new MimeBodyPart();
        messagePart.setText(body);
        System.out.println("Mime message body set!");

        // Set the email attachment file
        MimeBodyPart attachmentPart = new MimeBodyPart();
        FileDataSource fileDataSource = new FileDataSource(filename) {
            @Override
            public String getContentType() {
                return "application/octet-stream";
            }
        };
        attachmentPart.setDataHandler(new DataHandler(fileDataSource));
        attachmentPart.setFileName(fileDataSource.getName());
        System.out.println("Mail attachment info set!");

        // Add all parts of the email to Multipart object
        Multipart multipart = new MimeMultipart();
        multipart.addBodyPart(messagePart);
        multipart.addBodyPart(attachmentPart);
        message.setContent(multipart);
        System.out.println("Mail parts added!");

        // Send email
        Transport.send(message);
        System.out.println("Mail sent!");
    } catch (MessagingException e) {
        e.printStackTrace();
    }
}

我得到的错误只有在命令行运行时才会出现：

 Exception in thread "main" java.lang.NoClassDefFoundError: com/sun/mail/util/MailLogger
    at javax.mail.Session.initLogger(Session.java:221)
    at javax.mail.Session.<init>(Session.java:206)
    at javax.mail.Session.getInstance(Session.java:242)
    at VerifyUrl.sendEmail(VerifyUrl.java:186)
    at VerifyUrl.main(VerifyUrl.java:50)
 Caused by: java.lang.ClassNotFoundException: com.sun.mail.util.MailLogger
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 5 more

任何可能导致此问题的想法？

Answer 1

这是java开发人员面临的最常见问题。

其中java有包结构机制。
要运行使用其他包类/接口/枚举的任何java程序，您需要将其导入到类中。
如果您使用的是外部库或其他软件包，则需要在案例com.sun.mail.util.MailLogger中为该类设置类路径。
其中像eclipse和IntellijIdea这样的IDE会为你打包并设置类路径。
如果您尝试运行上述程序或任何其他程序，可以使用
之类的语法
java -cp /relative_path_to_your_dependency_jars ClassName

在你的情况下是这样的。

java -cp /downloadpath/javax.mail-1.5.0.jar YouMainClass

类似于编译类

java -cp /downloadpath/javax.mail-1.5.0.jar YouMainClass.java

Answer 2

这结果是类路径问题，也使用javax.mail而不是javax.mail-api。

问题现在解决了。

NoClassDefFoundError仅在通过命令行运行代码时发生

2 个答案: