The JDBC_DRIVER specifies what driver your going to use to connect your java code to mySql. The DB_URL specifices the url of your locally running mySql server. The last two are your login credentials ...

ActiveRecord-JDBC-Adapter (AR-JDBC) is the main database adapter for Rails' ActiveRecord component that can be used with JRuby. ActiveRecord-JDBC-Adapter provides full or nearly full support for: ...

Prior to the release of Java 9, Apache Derby was distributed along with the JDK and named JavaDB. As a result, it was common for developers interested in Java database connectivity (JDBC) to learn on ...