import org.springframework.web.util.UriComponentsBuilder;

public class test_uri {
    public static void main(String[] args) {
        String base = "https://accounts.google.com/o/oauth2/v2/auth?prompt=select_account";
        String full = UriComponentsBuilder.fromUriString(base)
            .queryParam("client_id", "123")
            .build().toUriString();
        System.out.println(full);
    }
}