I have tried accessing HTTP call using "Named Credential" option. 
Created named credential
Name/Label : localhost & http://localhost:8080

Below is my REST API call to access the external REST api,
URL : http:// localhost:8080/spring/home/restRecentActivity

In apex java class, provided below URL to perform HTTP request.
callout:localhost/spring/home/restRecentActivity

I have verified in logs, getting error message as 400 - BAD REQUEST. Please someone help in providing best samples & to pass the right URI.

Please help me to solve this issue.