The policy file should grant socket permission prior to granting URLPermission .The policy file should be.
grant Principal SysAdminPrincipal "sysadmin"
{
permission java.net.SocketPermission "127.0.0.1:8080","connect,resolve";
permission java.net.URLPermission "http://localhost:8080/HelloWorldREST/helloworld","GET";
};
grant Principal UserPrincipal "user"
{
};