javaweb发送邮电异常，怎么解决啊！！

Exception in thread "main" java.lang.NoClassDefFoundError: com/sun/mail/util/BEncoderStream
at javax.mail.internet.MimeUtility.doEncode(MimeUtility.java:664)
at javax.mail.internet.MimeUtility.encodeWord(MimeUtility.java:643)
at javax.mail.internet.MimeUtility.encodeText(MimeUtility.java:444)
at javax.mail.internet.MimeMessage.setSubject(MimeMessage.java:793)
at javax.mail.internet.MimeMessage.setSubject(MimeMessage.java:757)
at util.SimpleMailSender.sendTextMail(SimpleMailSender.java:48)
at service.UserServiceimpl.sendMail(UserServiceimpl.java:45)
at service.UserServiceimpl.main(UserServiceimpl.java:88)