How to write a function in a Web Service

So having a function code in JSP, example is this one:

function isitinstalled() {
		try {
			var myObj = new activity1(plugin.activity);
			if (myObj) { 
				return "activity123";
			} 
		} catch(e) {
			if (navigator.plugins[plugin.namename]) {
				return "me";
			} else {  
				return false;
			}
		}
		return false;
	}

How do I translate that code into a "Web Service" Coding java (like the ones with @WebParam (whatever = whatever). Sorry for another post, I'm exploring things and I'm a bit new to web services and my assignments need to be done. (Above is just a sample program.) Thanks guys! Your answers are much appreciated!