After deploying java web application giving 404– Internal Server Error

I am trying to deploy my java web application in Heroku from using eclipse IDE follow by this link: https://devcenter.heroku.com/articles/deploying-java-applications-to-heroku-from-eclipse-or-intellij-idea.

I have use WAR file to deploy this project.I have used mysql database locally.

This is github link of my project: https://github.com/sachin1830/SmOnlineExamProject.

This is my website link:

https://onlineexam1830.herokuapp.com/.

The index page working fine but when i am getting error when I am trying to login.

Error: HTTP Status 500 – Internal Server Error ,HTTP Status 404 – Not Found showing.

This is my first project and i am new in this please give me suggestions why this error coming and how i can resolve this error?
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Steps to repro the issue:

1. open website https://onlineexam1830.herokuapp.com/
2. Click on login on top
3. Enter username as nn
4. Enter password as uu

Expected: User should be able to login

Actual: Got error as 404.

Locally everything is working fine.