DispatcherNotFoundException 404 Error on ORDS Standalone and APEX

Symptom:

      After we install APEX 18.1 and ORDS 18.2 , we get 404 error on  Browser , Error stack is like:

DispatcherNotFoundException [statusCode=404, reasons=[]]    at oracle.dbtools.http.entrypoint.Dispatcher.choose(Dispatcher.java:87) 

Diagnosis:

     There are many reasons for that. One of reasons we hit is that the APEX_LISTENER  APEX_PUBLIC_USER  APEX_REST_PUBLIC_USER have not been setup correctly  when we install ORDS.war .
       The java -jar $ORDS_HOME/ords.war install advanced
       The process will read  ORDShome/ords/conf/*.xml , try to figure out the existing settings for the any new installation. It will skip apex listener setup if there are old settings there. Thus skip generating the xml files for each connections to DB.

      So in ords/conf/  , there should be 2 - 4 xml files .Each file define a connection pool to Database.  If you only see 1 xml, it means apex listeners settings are missing.

Solution:

    Remove ords_params.properties and *.xml  in ords/conf  and remove  standalone.properties  in ords/standalone
    Rerun java -jar $ORDS_HOME/ords.war install advanced
    Or  java -jar $ORDS_HOME/ords.war install simple  --- with correct parameter file