Master Null Checks in Java: When to Use StringUtils, ObjectUtils, and CollectionUtils

NullPointerException is a frequent bug; instead of sprinkling manual != null checks, you can use the appropriate utility classes provided by Spring or Apache Commons.

Step 1 – Identify the data type

The value may be a String , a custom Object , an Array , a List or a Map .

Step 2 – Choose the right utility class

String → StringUtils Object, Array, List, Map → ObjectUtils List/Map also →

CollectionUtils

Step 3 – Perform the check

Examples:

String str = "";
StringUtils.isEmpty(str); // true

Object obj = null;
ObjectUtils.isEmpty(obj); // true

Map<String,Object> map = Collections.emptyMap();
ObjectUtils.isEmpty(map); // true

List<Integer> list = Collections.EMPTY_LIST;
ObjectUtils.isEmpty(list); // true

Object[] objArr = null;
ObjectUtils.isEmpty(objArr); // true

The source of ObjectUtils.isEmpty(Object) checks for null, Optional, CharSequence, arrays, collections and maps, returning true when the value is considered empty.

public static boolean isEmpty(@Nullable Object obj) {
    if (obj == null) {
        return true;
    }
    if (obj instanceof Optional) {
        return !((Optional) obj).isPresent();
    }
    if (obj instanceof CharSequence) {
        return ((CharSequence) obj).length() == 0;
    }
    if (obj.getClass().isArray()) {
        return Array.getLength(obj) == 0;
    }
    if (obj instanceof Collection) {
        return ((Collection) obj).isEmpty();
    }
    if (obj instanceof Map) {
        return ((Map) obj).isEmpty();
    } else {
        return false;
    }
}

This method cannot detect a collection that contains a single null element; it only checks size. For such cases you need to inspect each element, e.g.:

Arrays.stream(list.toArray()).allMatch(ObjectUtils::isEmptyisNull);

For maps you can use CollectionUtils.isEmpty(map) which internally checks map == null || map.isEmpty().

public static boolean isEmpty(@Nullable Map<?, ?> map) {
    return map == null || map.isEmpty();
}

In summary, determine the data type, pick the corresponding utility class, and invoke its isEmpty (or isEmptyisNull) method to replace repetitive != null checks.