DFLib, a Java DataFrame library

DFLib is a lightweight pure Java implementation of a common DataFrame data structure. With DataFrame, you get essentially the data manipulation capabilities similar to SQL (filtering, joins, unions, and so on), only you done as step-by-step in-memory transformations that are easy to compose and to understand. DFLib comes with connectors for CSV, Excel, RDBMS, Avro, Parquet, JSON, etc. and can be easily adapted for other formats. It is open source and is distributed under the Apache License.

To get started, follow the documentation