I prefer placing the custom jar(s) specific to a package Java service and not global to IS.
Place it in /code/jars or /code/jars/static on the package file system on the IS server . On designer, you have to import the jars to your build path during compilation.
If you still want to place the jar globally where this jar is shared and accessible to the IS (default instance) then the path will be
C:\SoftwareAG103\IntegrationServer\instances\default\lib\jars\custom, restart the IS if you choose this location.
#Integration-Server-and-ESB#webMethods