HSQL Database Engine (HSqlDb) is a lightweight 100% Java SQL database engine developed at SourceForge since April 2001. HSqlDb is a relational database engine written in Java, with a JDBC driver, supporting a rich subset of ANSI-92 SQL (BNF tree format). It offers a small (less than 160K), fast database engine which offers both in memory and disk based tables. It is complete free under its licenses.
It is 100% pure Java database. Accordingly, it is easy for distribution
Features supported a rich subset of ANSI-92 SQL (BNF tree format)
Offers a small, fast, stable, and reliable database
Provides both embedded and server modes
Provides both in memory and disk based tables
It is free under HSqlDb licence
Use JDBC in Java to perform database query
jdbc driver: org.hsqldb.jdbcDriver
jdbc url: jdbc:hsqldb:/$path/$DB_NAME
Change readonly=true in $DB_NAME.proiperties file
Please refer to HSQL Database Engine Web site.