I want to do web search with java and I found GSA-JAPI does it work on web searching or it's used only on a website which I created for example.
The GSA-JAPI's purpose is to access and manage settings in a Google Search Appliance, which is an enterprise product Google sells. You can't use the GSA-JAPI to script any web searches, only manage a Google Search Appliance. It's used as an alternative to logging into the web based Admin Console.