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()

Correct way to check for null or empty or string containing only spaces is like this:

if(str != null && !str.trim().isEmpty()) { /* do your stuffs here */ }

isEmpty()

The java string isEmpty() method checks if this string is empty. It returns true, if the length of the string is 0 otherwise false e.g.

System.out.println("".isEmpty()); // Prints - True
System.out.println(" ".isEmpty()); //Prints - False 

Java 11 - isBlank()

The new instance method java.lang.String.isBlank() returns true if the string is empty or contains only white space, where whitespace is defined as any codepoint that returns true when passed to Character#isWhitespace(int).

boolean blank = string.isBlank();

Before Java 11

boolean blank = string.trim().isEmpty();

After Java 11

boolean blank = string.isBlank();