First you will have to rent a server machine (or more) and an administrator, get a protocol description for the GPS you are trying to implement, get a java developer to code a protocol server, plan and create a database, process the received messages and store them, get a web/java EE/Java FX or other GUI developer, register your app with the chosen map prividers, implement or find a map plugin to your ecosystem. Frankly, it’s not more than a few years if the quality is important.
Most of the times it’s not worth it as centralized solutions are nearly always more cost friendly, rapid, agile.
For example our service (http://corvusgps.com) does the same for you (actually while it’s in beta state – it’s free also) you will only have to get the right GPS devices (they should be supported by our system) and configure them to communicate to our server machines, and you can track them on our page’s map.
If there is a use-case that you need and we have not implemented yet – you can contact us and tell what you would like to see – and we will be eager to solve it for you.