How do I check that a Java String is not all whitespaces?

java

regex-patterns

string-manipulation

null-pointer-exception

byNikita Barsukov·Jan 6, 2025

Checking for non-whitespace characters in a Java String is as straightforward as using str.trim().isEmpty() or !str.isBlank() for Java 11+. For compact approaches, consider StringUtils.isNotBlank(str) from the Apache Commons Lang library. Here's the basic concept:

boolean isNotEmpty = !str.isBlank(); // Java 11+

For antiquated Java versions, we do:

boolean isNotEmpty = !str.trim().isEmpty(); // Pre-Java 11
// With Apache Commons Lang
boolean isNotEmpty = StringUtils.isNotBlank(str); // Fancy library

But don't rush off just yet - let's dive deeper into the intricacies of these methods, alternatives and important considerations!

Unicode and Regex to the rescue!

Standard .trim method is a great chap, but alas he's not adept with Unicode! Fear not, a detailed regex pattern is here to carry the day. Introducing .*\\S.*, adept at handling Unicode non-whitespace characters:

boolean hasNonWhiteSpace = str.matches(".*\\S.*"); // Not all heroes wear capes!

Before you get all excited, performance could be an issue here. Avoid overworking poor regex - save it for emergencies.

Null and empty - the insidious twins

Nothing quite puts a damper on your code's jamboree like a NullPointerException. So, remember to check if the string is null before messing with it:

boolean isNotEmpty = str != null && !str.trim().isEmpty(); // Hey Null, not on my watch!

A little tip from me to you, str.trim() will always give you back something, either an empty string or a trimmed string. It's not the disappearing type.

Java 8+ Streams for the modern coder

If you're part of the stream team, Java 8+ Streams can be your magic wand to identify non-whitespace:

boolean hasNonWhiteSpace = str.chars().anyMatch(Character::isWhitespace); // The Streamy award goes to...

A dose of functional programming makes your string operations fun and elegant. Exercise caution, streams can run wild.

StringUtils - your swiss army knife

If you're a fan of Apache Commons Lang, wield the StringUtils.isNotBlank(str) method - it's sharper than a trim:

boolean isNotEmpty = StringUtils.isNotBlank(str); // Swiss Army Knife of strings!

This method grabs null, empty and whitespace-only strings by the collar and tidies them up.

Regular expressions - Tough to master, sweet to use

While regex tools are the 'black belt' in string manipulation, remember their impact on cost and readability are equivalent to a turtle carrying a piano. Fast? No. Impressive? Definitely.

Anticipate the mischievous edge cases: Null, empty, filled with non-printable character strings! They can ruin your perfect program if left unattended.

Characters, characters everywhere

Everyone's unique, and so is the whitespace in your strings. Java 11's isBlank() is social and acknowledges this diversity, including spaces, tabs, and new line characters.