StringUtils.isBlank() checks that each character of the string is a whitespace character (or that the string is empty or that it's null). This is totally different than just checking if the string is empty.
From the linked documentation:
Checks if a String is whitespace, empty ("") or null.
StringUtils.isBlank(null) = true StringUtils.isBlank("") = true StringUtils.isBlank(" ") = true StringUtils.isBlank("bob") = false StringUtils.isBlank(" bob ") = false
For comparison StringUtils.isEmpty:
StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false
StringUtils.isEmpty("bob") = false
StringUtils.isEmpty(" bob ") = false
Warning: In java.lang.String.isBlank() and java.lang.String.isEmpty() work the same except they don't return true for null.
java.lang.String.isBlank() (since Java 11)
java.lang.String.isEmpty()
StringUtils.isBlank() checks that each character of the string is a whitespace character (or that the string is empty or that it's null). This is totally different than just checking if the string is empty.
From the linked documentation:
Checks if a String is whitespace, empty ("") or null.
StringUtils.isBlank(null) = true StringUtils.isBlank("") = true StringUtils.isBlank(" ") = true StringUtils.isBlank("bob") = false StringUtils.isBlank(" bob ") = false
For comparison StringUtils.isEmpty:
StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false
StringUtils.isEmpty("bob") = false
StringUtils.isEmpty(" bob ") = false
Warning: In java.lang.String.isBlank() and java.lang.String.isEmpty() work the same except they don't return true for null.
java.lang.String.isBlank() (since Java 11)
java.lang.String.isEmpty()
The accepted answer from @arshajii is totally correct. However just being more explicit by saying below,
StringUtils.isBlank()
StringUtils.isBlank(null) = true
StringUtils.isBlank("") = true
StringUtils.isBlank(" ") = true
StringUtils.isBlank("bob") = false
StringUtils.isBlank(" bob ") = false
StringUtils.isEmpty
StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false
StringUtils.isEmpty("bob") = false
StringUtils.isEmpty(" bob ") = false
If you want to use Guava to replicate the isBlank behaviour, I would use the following method instead:
Strings.nullToEmpty(str).trim().isEmpty()
When you have to accept input from human beings, you should be forgiving and strip leading and trailing whitespace from whatever text they type, if it makes sense in the particular application.
That said, using isBlank is only halfbaked. You also need to trim the strings before processing them further. So I suggest to use s = trim(s); before checking with isNullOrEmpty.