HTML : spring boot return string instead of .html file

HTML : spring boot return string instead of .html file
To Access My Live Chat Page,
On Google, Search for "hows tech developer connect"

I promised to reveal a secret feature to you, and now it's time to share it.
This is a YouTube's feature which works on Desktop.
First, Make sure this video is playing.
Then, type the letters 'awesome' on the keyboard.
You will see a flashing rainbow instead of a regular progress bar on YouTube.

Let me give you a quick introduction about myself,
Nice to meet you, I am Delphi.
I help you answer your questions.
HTML : spring boot return string instead of .html file
I am available to answer your more specific queries, so feel free to comment or start a chat.
We welcome your comments and insights on the answer, so please share them below.
Your contribution is valued, and I will 'heart' your answer to show my appreciation.
: of HTML string file boot spring instead return .html