This might be a little old school for many people here. I'm dating myself.

The framework was EJB. That shit was fucking boring and fizzled out.

The company I worked for built their own search engine for structured data. It was a precursor to ElasticSearch. In fact, Apache Lucene was our biggest competitor. We were way ahead of Lucene. We had features that Apache Solr had before Solr started. The problem was that we were closed source and paid. Then someone started Solr, and Solr+Lucene was as good as us and free. Our clients moved to Solr+Lucene seemingly overnight. That's when I left the company cuz they could literally not make payroll at one point. ElasticSearch essentially took Solr+Lucene, put it on the cloud, and made a lot of improvements.

The search engine was all running on a fleet of servers running Tomcat. There wasn't even a database. The data was all stored in fucking binary files.. or so I thought initially. Later, I learned that the data was stored in columnar format. The CTO and the architect had invented their own columnar file format. Which is pretty cool right now, but back then, it was weird when the whole world was on RDBMS. Also, I learned a lot of things that no one would even talk about. I learned how sharding data can help you scale. We essentially had our own map-reduce. I learned all this when AWS was in its infancy.

It was all very cool. But, throughout, I was blaming myself for procrastinating on learning EJBs and learning things that 95% of the industry doesn't understand. Procrastinating was the best thing that I did.