Eclipse：java.lang.NoClassDefFoundError：javax / activation / DataHandler

Question

我试图用java发送电子邮件。 这是代码：

String mailSmtpHost = "smtp.example.com";
String mailTo = "email@example.com";
        String mailFrom = "email@example.com";
        String mailSubject = "Email subject";
        String mailText = "Some text";
        Properties properties = new Properties();
        properties.put("mail.smtp.host", mailSmtpHost);
        Session emailSession = Session.getDefaultInstance(properties);
try {
            Message emailMessage = new MimeMessage(emailSession);
            emailMessage.addRecipient(Message.RecipientType.TO, new InternetAddress(mailTo));
            emailMessage.setFrom(new InternetAddress(mailFrom));
            emailMessage.setSubject(mailSubject);
            emailMessage.setText(mailText);
            emailSession.setDebug(true);
            Transport.send(emailMessage);
        }catch(Exception e) {
            System.out.println("Errore email: "+e.toString());
        }

当我编译项目时，在线：

Message emailMessage = new MimeMessage(emailSession);

......出现以下错误：

Exception in thread "main" java.lang.NoClassDefFoundError: javax/activation/DataHandler

注意：我使用java -version: 9.0.4

Answer 1

JDK 9默认禁用对许多javax。* API的访问，现在不推荐使用javax激活。

但是，您可以通过在运行时添加模块来解决此问题

"--add-modules java.activation".

Answer 2

下载并添加外部jakarta.activation-1.2.1.jar 是Jakarta Activation项目。