javamail new MimeMessage hangs - jakarta-mail

Question

If you provide correct values for emailSenderAddress and emailSenderPassword this snippet works in debug mode in Netbeans and in command line.
BUT if you don't add the import DataHandler, it works only in debug mode.
public class mailTest {
// dummy DataHandler to be sure to keep the import !
private DataHandler dh;
private void prepareMessage() {
java.util.Properties props = System.getProperties();
props.put("mail.smtps.host", "smtp.gmail.com");
props.put("mail.smtps.auth", "true");
// simple class derived from Authenticator not relevant for the current discussion
GMailAuthenticator auth = new GMailAuthenticator(<emailSenderAddress>, <emailSenderPassword>);
javax.mail.Session session = javax.mail.Session.getInstance(props, auth);
javax.mail.Message msg = new javax.mail.internet.MimeMessage(session);
System.out.println("new MimeMessage ok !");
}
public static void main(String[] args) {
mailTest mt = new mailTest();
mt.prepareMessage();
}
}
class GMailAuthenticator extends Authenticator {
String user;
String pw;
public GMailAuthenticator(String username, String password) {
super();
this.user = username;
this.pw = password;
}
public PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(user, pw);
}
}

Answer 1

What JDK version are you using? DataHandler is part of the javax.activation (JavaBeans Activation Framework, aka JAF) API, which is included in JDK 8 and earlier but not in JDK 11. JavaMail needs JAF, whether you use it explicitly in your program or not. On JDK 11, you'll need to add it to your project explicitly. If you have a Maven project, you can add a dependency on com.sun.activation:javax.activation:1.2.0.