Oracle 12c Express EM Configuration

Oracle 12c doesn't have the same EM which was used to be till 11g. The 12c comes with express EM.

How to configure a express EM in 12c.
Login to the database and execute the below command to verify whether Express EM is configured or not.
select dbms_xdb_config.gethttpsport () from dual;

If the above statement returns any row(that will be the port number), that means the Express EM is configured. Use that port number to connect to EM(use https) as
https://<hostname>:<port_number>/em

Else on the server first verify which port is free using the below mentioned command. If for a port number no output is returned that may mean its free and can be used(please verify that other applications are not using that port)
netstat -an|grep <port number> (We can use any port e.g. 1158)

Then connect to the database as sys user and execute the below command;
exec dbms_xdb_config.sethttpsport (1158);

select dbms_xdb_config.gethttpsport () from dual;

You can use the above port to connect to the Express EM.

The following points you must remember while configuring the Express EM
1. It uses https 
2. The parameter DISPATCHERS must be set.

SQL> show parameter dispatchers

NAME               TYPE        VALUE
------------------ ----------- ------------------------------
dispatchers        string      (PROTOCOL=TCP)(SERVICE=orclXDB)

If its not set, we need to set it 
e.g. for my SID orcl I have set using the below command
alter system set dispatchers='(PROTOCOL=TCP)(SERVICE=orclXDB)' scope=both;