How to check whether a Collection is Null or Empty in Java

Managing collections efficiently is crucial in Java, especially when ensuring they are not null or empty before performing operations. This guide will walk you through how to check if a collection is null or empty using both the Apache Commons Collections and Spring Framework utilities, along with native Java approaches.

Before manipulating collections—such as lists, sets, and maps—it’s essential to ensure they are neither null nor empty. This verification prevents common bugs like NullPointerExceptions and enhances the reliability of your application.

Native Java Approach

Check for Null or Empty

List<String> myList = getMyList();  
if (myList == null || myList.isEmpty()) {
    System.out.println("The list is null or empty.");
}

This native approach uses straightforward Java to check for null and then checks if the list is empty using isEmpty().

Also Read: How to Create Immutable Objects in Java

Using Apache Commons Collections

Apache Commons Collections library simplifies many operations, including checking for null or empty collections.

Add Dependency

For Maven projects, add the following dependency to your pom.xml

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.4</version>
</dependency>

Utilize CollectionUtils

import org.apache.commons.collections4.CollectionUtils;

if (CollectionUtils.isEmpty(myList)) {
    System.out.println("The list is null or empty using Apache Commons.");
}

CollectionUtils.isEmpty() checks both nullity and emptiness in one method call, simplifying the code.

Using Spring Framework’s CollectionUtils

Spring also provides a CollectionUtils class that offers null-safe methods to work with collections.

Using Spring’s CollectionUtils

import org.springframework.util.CollectionUtils;

if (CollectionUtils.isEmpty(myList)) {
    System.out.println("The list is null or empty using Spring Framework.");
}

Similar to Apache Commons, Spring’s CollectionUtils.isEmpty() method provides a null-safe way to check if a collection is empty.

Also Read: How to configure JaCoCo for Code Coverage in Spring boot Applications

When to Use Apache Commons vs. Spring CollectionUtils

Apache Commons Collections: Ideal for applications that need robust collection manipulation capabilities beyond what Java provides natively. It’s also a good choice if your project does not already use Spring.
Spring Framework’s CollectionUtils: Best for applications that are already built with Spring, to keep dependencies consistent and leverage Spring’s comprehensive ecosystem.

Best Practices

When dealing with collections:

Always check for null and empty states before using them.
Consider using utility libraries like Apache Commons to simplify your code.
Include these checks as part of your standard validation routines to avoid repetitive bugs.