I need to access data from an external oracle database from my application android to update the local database application, but I don\'t know what would be the best way to
There is a simpler way than writing a WebService and still keeping the same level of security: use a Virtual JDBC Driver that uses a three-tier architecture: your JDBC code is sent through HTTP to a remote Servlet that filters the JDBC code (configuration & security) before passing it to the Oracle JDBC Driver. The result is sent you back through HTTP. There are some free software that use this technique. Just Google " Android JDBC Driver over HTTP".