I've been using Spring for about 5 years, have written many large applications in it, most of them over 100k lines of code - the one I'm currently working on has close to 300k lines of code in Java + Spring (split into two separate applications) and about a million+ lines of html + dart.

Build your UI in pure HTML5 + JS / Dart / Jquery + CSS3 (or even use a JS / Dart framework if you want) and let it call some APIs via AJAX - avoid using Spring Thymeleaf, JSP, JSF or any of the Java frontend frameworks - those will slow you down; reloading your container every time you make a change is not productive unless you use something like Jrebel or the Spring equivalent called Spring Loaded which will load changes in realtime even before you can hit the browser refresh. My preference is to build my UI in Dart and the backend including APIs all in Java + Spring.

Expose your APIs via Spring MVC, you can secure those APIs using Spring Security, to get database connectivity (I'm assuming you're going for something like MySQL / PostgreSQL / MariaDB / ...), Hibernate is usually a great fit for relational database ORM mapping and Spring integrates Hibernate like a glove. If you're not going to be doing a lot of database work, you can also get away using straight SQL in your code, but this will potentially leave you open to SQL injection attacks, Hibernate takes care of sanitising your inputs for you.

To get multiple Spring applications chatting with each other, Spring AMQP will allow you to communicate via RabbitMQ. If you need to move data around from email, FTP, files or a gazillion other channels, Spring Integration will sort that out for you often in less than 5 lines of code. If your app needs some sort of SOAP interface for corporates to integrate into, Spring Web Services will sort that out for you, just build the XSD and the WSDL will be generated for you. Need to setup permissions via LDAP (a requirement by many corporates), Spring LDAP has you covered and can be integrated into Spring Security without much trouble.

To get you started in under 5 minutes, use this application builder, choose the components you need under advance, download the zip file and start writing business logic: start.spring.io

You can consider using Spring Framework (http://spring.io), if you prefer building your app in Java. Its really flexible, robust, well documented and easy to start framework. You can separate your app to different small micro services and make them use different technologies depends on what that micro service is gonna be doing. (e.g. data_processing -> python. etc.) That way its gonna be easier to manage and scale your app.

Play with Scala