See "System procedures for storing jar files in a database" in the Derby Reference Manual for reference information about the jar file system procedures and complete syntax.
Pay particular attention to the sections on execute privileges for the sqlj.install_jar and sqlj.replace_jar procedures. Since these procedures can be used to install arbitrary code (possibly from across the network) that runs in the same Java Virtual Machine as the Derby database engine, both authentication and SQL authorization should be enabled, and execute privileges should be granted only to trusted users.