What does regular expression \\s,\\s do?

That regex "\\s*,\\s*" means:

which will split on commas and consume any spaces either side

\s stands for "whitespace character".
It includes [ \t\n\x0B\f\r]. That is: \s matches a space( ) or a tab(\t) or a line(\n) break or a vertical tab(\x0B sometimes referred as \v) or a form feed(\f) or a carriage return(\r) .

\\s*,\\s*

It says zero or more occurrence of whitespace characters, followed by a comma and then followed by zero or more occurrence of whitespace characters.

These are called short hand expressions.

You can find similar regex in this site: http://www.regular-expressions.info/shorthand.html

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