Note: If there is a better venue to ask this question, instead of just closing my question, please suggest a better place for it.

I have been trying to find a simple, self-hosted (i.e., non-cloud based) object storage solution that can be used by Java applications. This will be used for a company-internal application and will be used primarily to facilitate shared data storage between independent, non-interacting pieces of code, running in separate threads.

These are my requirements:

• Free or open-source.
• Actively being developed/maintained.
• Does not require a “schema”. I need to be able to store data in any Java language supported data type and data structure. Support for a schema-based system is fine as long as it’s not mandatory.
• The storage can be in-memory or disk-based. I am anticipating typical data sizes well under 1 MB.
• Having the ability to search for information by some criteria would be a very nice to have.
• Having the ability to extract information that meets some criteria would be a very nice to have.
• Having the ability to be notified when a storage event occurs, would be a nice to have.
• Does not require any third-party dependencies.

I have done searches and found a number of potential solutions that might match. However, some seem way more complicated that what I want to deal with, others seem to require a schema definition. I focused on ones that appeared to be compatible with Java and ignored the rest. It’s not clear whether any of the non-Java options could somehow, perhaps be usable.

I spent some time trying out one, called Nitrite (https://nitrite.dizitart.com/index.html), which seemed very promising. Unfortunately, its search capability does not work as I expected, or as I need. Perhaps there is something I’m missing that checks that important box. I have nor ruled it out, but will need to do a lot of work myself to make up the lack of functionality I need. If anyone has used Nitrite and might be able to help, it would be much appreciated.