How to get JDK source code

git clone https://github.com/openjdk-mirror/jdk.git
cd jdk
git checkout jdk8u/jdk8u/master

And go ahead find the class. Most classes can be found under /src/share/classes/,
for example,/src/share/classes/sun/nio/channels/FileChannelImpl.java

Reference: https://stackoverflow.com/questions/42307687/get-complete-jdk-source-code-in-intellij-or-other-ide

What is Rest

What is REST?

“Rest is architectural style for distributed hypermedia systems”: REpresentational State Transfer (Rest != http)

Data and functionality are resources.

Resources are accessible using URI.

The resources are acted upon by using simple operations. HTTP is an implementation of a standardised interface.

Resources can have Metadata to express representation format, control caching, auth and access_control, etc.