jarsigner "Only one alias can be specified"

I was getting the same error.

I resolved it by renaming the folders in my path

c:\this is a folder\ replaced with c:\this_is_a_folder\

jarsigner doesn't like spaces in folders

Remove the space from Folder Name like

jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.jks D:\AndroidProject\CheckFinalCodeNew\CheckFinalCode\platforms\android\build\outputs\apk\android-release-unsigned.apk my-alias

The problem would be resolve

Just put quotes around the filename(s) with spaces. You need to quote arguments with spaces in them, to any program. Nothing to do with jarsigner whatsoever.