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()

To collect all the comments and putting some additional information. Here we are:

JDK 11

String class have isBlank() for checking blank string.

Less then JDK 11

There is no built in function. We have to tackle it is different way.

1. First check whether the string is null
2. If it is not null then Trim the string and check its length

Example:

1. temp == null || temp.trim().length() == 0
2. or, temp == null || temp.trim().isEmpty(). Note: is empty is internally checking length

Apart from this, there are some 3rd party Libs available that do this for us Like,

Apache common lang

It has various method for String. For our case StringUtils.isBlank is suitable candidate. I recommend you to read other string related methods too.

Guava

This lib also provide methods for string.

Example: Strings.isNullOrEmpty()

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();

The library you want to use is the org.apache.commons.lang.StringUtils and you have to add it to your classpath manually or add it as a dependency to your gradle configuration or any other build tool you are using.

IntelliJ does not know the library out of the box as it is not part of the JDK.