Can the Oracle database send requests to a Servlet?
Using UTL_HTTP
Yes, you can send HTTP requests from the Oracle database. Here's a nice blog post that summarises how you can do it using the UTL_HTTP package:https://oracle-base.com/articles/misc/utl_http-and-ssl
An example from the Oracle manual:
SET SERVEROUTPUT ON SIZE 40000DECLARE req UTL_HTTP.REQ; resp UTL_HTTP.RESP; value VARCHAR2(1024);BEGIN UTL_HTTP.SET_PROXY('proxy.my-company.com', 'corp.my-company.com'); req := UTL_HTTP.BEGIN_REQUEST('http://www-hr.corp.my-company.com'); UTL_HTTP.SET_HEADER(req, 'User-Agent', 'Mozilla/4.0'); resp := UTL_HTTP.GET_RESPONSE(req); LOOP UTL_HTTP.READ_LINE(resp, value, TRUE); DBMS_OUTPUT.PUT_LINE(value); END LOOP; UTL_HTTP.END_RESPONSE(resp);EXCEPTION WHEN UTL_HTTP.END_OF_BODY THEN UTL_HTTP.END_RESPONSE(resp);END;Alternative using Oracle AQ
If you want some intermediary layer, you might also use Oracle AQ, which I personally find more powerful:https://docs.oracle.com/database/121/ADQUE/aq_intro.htm
Using Oracle AQ, you could for instance bypass the HTTP layer and access whatever the Servlet is calling internally, directly.