The & character in URL will break the curl command in *nix shell due to its default behavior for background process. This trick solved my problem
curl --proxy squid-proxy-server-name:port-number $url
There might be more than one Java classes in a Maven project that contains the main() function. To pick up a specific one to run, you can try the following command:
mvn exec:java -Dexec.mainClass="my_main_class_name"
In case the memory is not enough, try the following command:
where 1024m is the max heap memory