How to match "any character" in regular expression?

Yes, you can. That should work.

• . = any char except newline
• \. = the actual dot character
• .? = .{0,1} = match any char except newline zero or one times
• .* = .{0,} = match any char except newline zero or more times
• .+ = .{1,} = match any char except newline one or more times

Use the pattern . to match any character once, .* to match any character zero or more times, .+ to match any character one or more times.

Yes that will work, though note that . will not match newlines unless you pass the DOTALL flag when compiling the expression:

Pattern pattern = Pattern.compile(".*123", Pattern.DOTALL);
Matcher matcher = pattern.matcher(inputStr);
boolean matchFound = matcher.matches();