public String greetServer(String input) throws IllegalArgumentException {
		// Verify that the input is valid. 
		if (!FieldVerifier.isValidName(input)) {
			// If the input is not valid, throw an IllegalArgumentException back to
			// the client.
			throw new IllegalArgumentException(
					"Name must be at least 4 characters long");
		}

		String serverInfo = getServletContext().getServerInfo();
		String userAgent = getThreadLocalRequest().getHeader("User-Agent");

		// Escape data from the client to avoid cross-site script vulnerabilities.
		input = escapeHtml(input);
		userAgent = escapeHtml(userAgent);

		return "Hello, " + input + "!<br><br>I am running " + serverInfo
				+ ".<br><br>It looks like you are using:<br>" + userAgent;
	}