Let me add.
I want to open <project directory>/Materials/index.html with Eclipse-built-in web browser.
This file is the artifact of my Visual Testing in Katalon Studio project. I want to view it in Katalon Studio natively rather than going out to Mac Finder/Windows Explorer to click it to open with external browsers.
Why?
Windows Explore is a very much greedy software. When I open a folder <project>/Materials/ and click the index.html in it, the Explorer takes software lock for the file. If I execute other Java program (e.g., a test case in Katalon Studio) which tries to delete the index.html, a contention occurs. Windows OS does lock the file and force Java program not to delete it. In order to free the lock & contention between Windows OS and a Java process, I have to close Explorer, or in a worst case I have to stop and restart Windows OS. This problem is very annoying. Therefore I want to refrain from Windows Explorer as much as possible.