Are you looking for a way to use Papercut with java mail API? If so, then I will share the method I stumbled upon while searching for the same.
As a software developer, I too got stuck with this problem. I had to check and verify whether the mail content is in place while sending a mail using JAVA mail API. During Development phase we cannot send the mail directly to someone. We have to make sure that the mail is presentable to the end user. The code for java mail is as shown below