StringUtils

About

StringUtils is a utility class provided by Apache Commons Lang that contains a large number of static helper methods for working with strings.

Unlike the standard Java String class, which is immutable and provides limited methods, StringUtils makes string manipulation simpler, safer, and less error-prone, especially when dealing with null values or empty strings.

Characteristics

• All methods are static, and the class cannot be instantiated.

• Designed to be null-safe: methods do not throw NullPointerException if input is null.

• Includes checks, transformation, comparison, abbreviation, joining, splitting, and more.

• Very commonly used in enterprise Java applications, especially with Spring Boot.

Maven Dependency & Import

If we don’t already have it:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version> <!-- or latest stable -->
</dependency>

import org.apache.commons.lang3.StringUtils;

Common Categories of Methods

Here are the most commonly used method categories:

1. Null and Empty Checks

Method	Description
isEmpty(String str)	Returns true if the string is null or empty
isNotEmpty(String str)	Opposite of isEmpty()
isBlank(String str)	Returns true if the string is null, empty, or whitespace only
isNotBlank(String str)	Opposite of isBlank()
defaultIfEmpty(str, "N/A")	Returns a default value if string is empty or null

Example:

String input = null;
if (StringUtils.isBlank(input)) {
    // safe to check without NullPointerException
}

2. Trimming and Removing

Method	Description
strip(str)	Trims whitespace (null-safe)
stripToEmpty(str)	Trims and returns "" instead of null
stripToNull(str)	Trims and returns null if result is empty
remove(str, char)	Removes all occurrences of a character
deleteWhitespace(str)	Removes all whitespace characters

3. Comparison

Method	Description
equals(str1, str2)	Null-safe equals comparison
equalsIgnoreCase(str1, str2)	Null-safe equals comparison ignoring case
compare(str1, str2)	Null-safe lexicographical comparison
startsWith(str, prefix)	Null-safe prefix check
endsWith(str, suffix)	Null-safe suffix check

4. Substring and Search

Method	Description
substringBetween(str, open, close)	Gets substring between two markers
contains(str, search)	Checks if a string contains a sequence
countMatches(str, sub)	Counts how many times a substring appears
indexOfDifference(str1, str2)	Finds first differing index between two strings

5. Join and Split

Method	Description
join(array, separator)	Joins array of strings with a delimiter
split(str, separator)	Splits a string into an array by delimiter
splitByWholeSeparator(str, separator)	Splits by whole string separator

6. Capitalization and Case

Method	Description
capitalize(str)	Capitalizes the first character
uncapitalize(str)	Makes the first character lowercase
swapCase(str)	Swaps case of all characters

7. Abbreviation and Padding

Method	Description
abbreviate(str, maxWidth)	Shortens a string and appends "..."
leftPad(str, size, padChar)	Pads from left to reach desired size
rightPad(str, size, padChar)	Pads from right to reach desired size
repeat(str, count)	Repeats the string multiple times

8. Replacing

Method	Description
replace(str, search, replace)	Replaces all occurrences
replaceEach(str, search[], replace[])	Replaces multiple strings
replacePattern(str, regex, replacement)	Regex-based replacement

Why Use StringUtils Instead of Java String Methods?

Concern	Java String	StringUtils Advantage
Null handling	Throws exceptions	Null-safe
Common tasks	Manual/verbose	Simple static methods
Consistency	Varies	Centralized utility approach
Readability	Lower	More expressive method names