Java Regular Expression Test Online and cheat sheet

http://www.fileformat.info/tool/regex.htm

Here is another good online site to test regular expression

http://www.regexr.com/

http://regex101.com/

https://www.debuggex.com/r/EkIvhuQ8TmetiL5q

cheat sheet
http://www.rexegg.com/regex-quickstart.html