Hi Keerthi,
Apart from Coding there is one option available through Authentication logs,this is tested in NW7.3 iam not sure which version you are using if you are using 7.0 then please check if this is available in 7.0 or not.
1) Go to NWA
2) Go to troubleshooting and logs section
3) Open log viewer and choose Authentication logs from the logs option
4) Specify the time frame in filter and choose everywhere for the logs to be picked up in generated report ,this wil gather authentication data from all server nodes.
5) these logs will show each and every login performed bu Useres and it also shows how many times user have logged in to a particular application,choose IRJ as the application.
6) Export the content to excel file and apply filter ,choose aplication as IRJ and choose date and time and select a user it will show all login with the date and time.
7) You can feed this data to a predefined excel format and pull out necessary info ,only you need to develop an excel template for your reporting purpose and manually logs requires to be pulled in from NWA to feed the excel .
this is another way which does not involve any java coding and tested on NW7.3 versions of Portal.
hope this helps.
Thx,
Siddharth