• Very fast, open source, JDBC API
• Embedded and server modes; disk-based or in-memory databases
• Transaction support, multi-version concurrency
• Browser based Console application
• Encrypted databases
• Fulltext search
• Pure Java with small footprint: around 2.5 MB jar file size
• ODBC driver

More information: https://h2database.com

Download latest version or add to pom.xml:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>2.2.224</version>
</dependency>

• Tutorial
• SQL commands
• Functions, aggregate functions, window functions
• Data types

• Issue tracker for bug reports and feature requests
• Mailing list / forum for questions about H2
• 'h2' tag on Stack Overflow for other questions (Hibernate with H2 etc.)