Goal:
      To change the Web Listener Port number in Oracle E-Business Suite Release 12
 
This will be illustrated with a practical example using the following Hostname,Domain, Port numbers:
 
     -Host Name: myhost
     -Domain Name: oracle.com
     -Port Number  that we want to change: 8001
     -Port Number  that we wish to be changed  to:  8002
     -Protocol : HTTP

Solution

1- Open your  Context XML file for edit  through OAM
 
2- Change the value from 8001 to be 8002 on the following lines:
      <web_port oa_var="s_webport" oa_type="PORT" base="8000" step="1" range="-1" label="Web Listener Port">8001</web_port>
      <activewebport oa_var="s_active_webport" oa_type="DUP_PORT"  base="8000" step="1" range="-1" label="Active Web Port">8001</activewebport>
    <login_page oa_var="s_login_page">http://myhost.oracle.com:8001/OA_HTML/AppsLogin</login_page>
    <chronosURL oa_var="s_chronosURL">http://myhost.oracle.com:8001/oracle_smp_chronos/oracle_smp_chronos_sdk.gif</chronosURL>    

<oa_var="s_endUserMonitoringURL">http://myhost.oracle.com:8001/oracle_smp_chronos/oracle_smp_chronos_sdk.gif</EndUserMonitoringURL>
    <externURL oa_var="s_external_url">http://myhost.oracle.com:8001</externURL>
   <httplistenparameter oa_var="s_http_listen_parameter">8001</httplistenparameter>

3- Save your settings

4- Run Autoconfig for changes to take place

5- Try to login again through:
        http://myhost.oracle.com:8002
    The URL should be displayed successfully