What if oracle12c's em is unreachable?

Install the Oracle 12c, want to experience the next EM Express, lack of discovery can not be used, what should I do? 12c em is no longer as cumbersome as the previous version configuration, of course, there are not so many features, only need to enable the corresponding port, see:
To manually configure the HTTPS port for EM Express:
1. Configure and start the Oracle Net Listener (the Listener). You can use Lsnrctl to start, stop, and view the status of the listener.

2. If the listener is running in a nonstandard port (for example, not 1521) and then the Init.ora file for the database you w Ant to manage using EM Express must contain a Local_listener entry so and the HTTPS port can register with the Correc
Listener. The Local_listener entry references a tnsnames entry that points to the correct listener. For example:
Local_listener=inst1
Where Inst1 is a tnsnames entry defined in Tnsnames.ora that points to the listener. For example:
Inst1= (description= (address= (protocol=tcp) (Host=host_name) (port=1234) (connect_data=) (service_name=service_name ) (server=dedicated)))
In this example, 1234 are the nonstandard port on which the listener have been configured to listen.
3. Enable the TCP dispatcher by adding the following entry to the Init.ora file for the database you want to manage using EM Express:
Dispatchers= "(protocol=tcp) (SERVICE=XDB)"
For example, if the database SID was ORCL, then the entry would be:
Dispatchers= "(protocol=tcp) (SERVICE=ORCLXDB)"
4. Restart the database So, the changes made in the Init.ora file take effect.
5. Use the PL/SQL procedure dbms_xdb_config. Sethttpsport to set the HTTPS port for EM Express. This would update the HTTPS port in the Xdbconfig.xml file in the Oracle XML DB Repository. You must connect as Sys/as SYSDBA to run the procedure. For example:

Sql> exec dbms_xdb_config. Sethttpsport (5500);

6. To access EM Express, enter a URL in the following format in a Web browser:

https://database-hostname:portnumber/em/

For example:

https://mydbhost.example.com:5500/em/

When prompted is your username and password, log in as a user with DBA privilege (such as SYSTEM).

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What if oracle12c's em is unreachable?