H2 Database is a relational database engine built in pure Java. Actively developed by someone with a long history of making such products. Open-source and free-of-cost.
Can be used either embedded in your Java app, or run separately as a database server.
H2 could certainly handle your data and much more.
By default, H2 stores your data to disk in persistent fashion, with ACID compliant transactions to protect against corruption during a crash. Optionally, you can configure to run as an In-Memory database but then your data disappears after a crash or shutdown.
You will need to learn about relational databases in general, about H2 specifically, and about how to communicate to a database from Java via JDBC with SQL.
By the way, you should always have a primary key, even with a single table. If your data does not already contain a unique identifier, assign either a sequential number or a UUID value to each row upon INSERT.
Another embedded relational database engine is Apache Derby, formerly IBM Cloudscape. Also distributed by Sun/Oracle as Java DB. Written in pure Java.