Java Mail 找不到类 MimeMessage

Question

这是Mail类的代码(里面有一个main，但原因很简单，这样解决这个问题似乎很简单):

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.Properties;

public class Mail {

    public static void main(String [] args) {
    // Recipient's email ID needs to be mentioned.
    String to = "abcd@gmail.com";

    // Sender's email ID needs to be mentioned
    String from = "mail";
    String psw = "password";

    // Assuming you are sending email from localhost
    String host = "localhost";

    // Get system properties
    Properties properties = System.getProperties();

    // Setup mail server
    properties.setProperty("mail.smtps.host", host);
    properties.setProperty("mail.user", from);
    properties.setProperty("mail.password", psw);

    // Get the default Session object.
    Session session = Session.getDefaultInstance(properties);

    try {
        // Create a default MimeMessage object.
        MimeMessage message = new MimeMessage(session);

        // Set From: header field of the header.
        message.setFrom(new InternetAddress(from));

        // Set To: header field of the header.
        message.addRecipient(Message.RecipientType.TO, new                        InternetAddress(to));

        // Set Subject: header field
        message.setSubject("This is the Subject Line!");

        // Now set the actual message
        message.setText("This is actual message");

        // Send message
        Transport.send(message);
        System.out.println("Sent message successfully....");
    } catch (MessagingException mex) {
        mex.printStackTrace();
    }
  }
}

这是我运行后看到的终端:

Exception in thread "main" java.lang.NoClassDefFoundError: javax/activation/DataSource
    at Mail.main(Mail.java:35)
Caused by: java.lang.ClassNotFoundException: javax.activation.DataSource
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)
... 1 more

Process finished with exit code 1

错误发生:

MimeMessage message = new MimeMessage(session);

Answer 1

您要么需要告诉 JDK 9 公开包含但隐藏的 java.activation 模块，要么需要在项目中显式包含 JavaBeans Activation Framework(JAF；javax.activation)jar 文件。

通过将 --add-modules java.activation 添加到 java 命令行来执行前者。

后者可以通过使用此 Maven 依赖项来完成:

<dependency>
  <groupId>com.sun.activation</groupId>
  <artifactId>javax.activation</artifactId>
  <version>1.2.0</version>
</dependency>