Of course! The term "Java StringUtils" almost always refers to the StringUtils class from the Apache Commons Lang library. This is an incredibly popular and essential utility library for Java developers.

While Java's standard library (java.lang.String) has many useful methods, the Commons Lang StringUtils class fills in many common gaps, making string manipulation tasks much simpler and less error-prone.

Here’s a comprehensive guide covering everything you need to know.

What is Apache Commons Lang StringUtils?

It's a utility class in the Apache Commons Lang library that provides static methods for performing common operations on String objects that are null-safe.

Key Benefit: It prevents NullPointerException and simplifies code by handling null inputs gracefully.

How to Add it to Your Project

You need to include the Apache Commons Lang dependency in your build file.

For Maven (pom.xml):

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version> <!-- Check for the latest version -->
</dependency>

For Gradle (build.gradle):

implementation 'org.apache.commons:commons-lang3:3.14.0' // Check for the latest version

Core Categories of Methods

The methods can be grouped into several categories. We'll look at the most useful ones with examples.

A. Null-Safe Checks and Basic Operations

This is the most common reason developers use this library. Standard Java methods like "someString".length() will throw a NullPointerException if the string is null.

Example:

import org.apache.commons.lang3.StringUtils;
public class StringUtilsExample {
    public static void main(String[] args) {
        String nullString = null;
        String emptyString = "";
        String blankString = "   ";
        String normalString = "Hello";
        System.out.println("Is nullString empty? " + StringUtils.isEmpty(nullString)); // true
        System.out.println("Is emptyString empty? " + StringUtils.isEmpty(emptyString)); // true
        System.out.println("Is blankString blank? " + StringUtils.isBlank(blankString)); // true
        System.out.println("Is normalString blank? " + StringUtils.isBlank(normalString)); // false
        // Standard Java would throw NPE here
        // System.out.println(nullString.length()); 
        // StringUtils handles it safely
        System.out.println("Length of nullString: " + StringUtils.length(nullString)); // 0
        System.out.println("Default for nullString: '" + StringUtils.defaultString(nullString) + "'"); // ''
        System.out.println("Default for emptyString: '" + StringUtils.defaultIfEmpty(emptyString, "DEFAULT") + "'"); // 'DEFAULT'
    }
}

B. Checking for Substrings

Example:

String text = "Apache Commons Lang is great";
System.out.println(StringUtils.contains(text, "Commons")); // true
System.out.println(StringUtils.contains(text, "common")); // false
System.out.println(StringUtils.containsIgnoreCase(text, "common")); // true
System.out.println(StringUtils.startsWith(text, "Apache")); // true
System.out.println(StringUtils.endsWith(text, "great")); // true

C. Substring and Manipulation

Example:

String path = "/home/user/documents/report.txt";
System.out.println(StringUtils.substringAfter(path, "/")); // home/user/documents/report.txt
System.out.println(StringUtils.substringBefore(path, "/")); // (empty string)
System.out.println(StringUtils.substringAfterLast(path, "/")); // report.txt
System.out.println(StringUtils.substringBeforeLast(path, "/")); // /home/user/documents
String xmlTag = "<name>John Doe</name>";
System.out.println("Name is: " + StringUtils.substringBetween(xmlTag, "<name>", "</name>")); // John Doe

D. Splitting and Joining

Example:

String csvData = "apple,banana,cherry,date";
String[] fruits = StringUtils.split(csvData, ',');
System.out.println(Arrays.toString(fruits)); // [apple, banana, cherry, date]
List<String> colors = Arrays.asList("red", "green", "blue");
String colorString = StringUtils.join(colors, " - ");
System.out.println(colorString); // red - green - blue

E. Padding and Trimming

Example:

String text = "123";
System.out.println("'" + StringUtils.leftPad(text, 5, '0') + "'"); // '00123'
System.out.println("'" + StringUtils.rightPad(text, 8, '-') + "'"); // '123-----'
String messyText = "  some text  ";
System.out.println("->" + StringUtils.strip(messyText) + "<-"); // ->some text<-

F. Case Conversion

Example:

String name = "java developer";
System.out.println(StringUtils.capitalize(name)); // Java developer
System.out.println(StringUtils.swapCase(name)); // JAVA DEVELOPER
System.out.println(StringUtils.reverse(name)); // repoleved avaj

Java 8+ Alternatives (The java.util.stream Approach)

With the release of Java 8, many of these tasks can be accomplished using the Stream API and Optional. This can sometimes lead to more expressive, functional-style code.

Example: Checking for null or empty

String myString = null;
// Old way (StringUtils)
boolean isEmpty = StringUtils.isEmpty(myString); // true
// Java 8+ way
boolean isEmptyJava8 = Optional.ofNullable(myString).map(String::isEmpty).orElse(true); // true
boolean isNotEmptyJava8 = Optional.ofNullable(myString).map(s -> !s.isEmpty()).orElse(false); // false

Example: Joining a List

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
// Old way (StringUtils)
String joined = StringUtils.join(names, ", "); // "Alice, Bob, Charlie"
// Java 8+ way
String joinedJava8 = String.join(", ", names); // "Alice, Bob, Charlie"

Example: Splitting a String

String data = "a,b,c";
// Old way (StringUtils)
String[] parts = StringUtils.split(data, ','); // ["a", "b", "c"]
// Java 8+ way (using a regex, be careful with special characters)
String[] partsJava8 = data.split(","); // ["a", "b", "c"]

While Java 8+ provides excellent alternatives, StringUtils often remains more concise and readable for many common operations, especially when dealing with null inputs.

Summary: When to Use StringUtils vs. Java Standard Library

Conclusion: The Apache Commons Lang StringUtils is a timeless, powerful, and highly recommended tool for any Java project. It improves code robustness by handling null values and provides a rich set of utility methods that simplify common string operations.