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

I’m trying to send an email in java. Here’s the code:

String mailSmtpHost = "smtp.example.com";
String mailTo = "[e-mail]";
        String mailFrom = "[e-mail]";
        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());
        }

When I compile the project, on line:

Message emailMessage = new MimeMessage(emailSession);

…the following error comes out:

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

Note: I’m using java -version: 9.0.4

Answer

JDK 9 disables access to many of the javax.* APIs by default, javax activation is now deprecated.

However you can resolve it with adding the module at run time

"--add-modules java.activation".