When to Use StringUtils.isEmpty vs isBlank in Java?

org.apache.commons.lang.StringUtils provides common string operations. The most frequently used null/empty checks are isEmpty(String str) and isBlank(String str).

Analysis

We compare the source implementations:

public static boolean isEmpty(String str) {
    return str == null || str.length() == 0;
}
public static boolean isNotEmpty(String str) {
    return !isEmpty(str);
}
public static boolean isBlank(String str) {
    int strLen;
    if (str != null && (strLen = str.length()) != 0) {
        for (int i = 0; i < strLen; ++i) {
            if (!Character.isWhitespace(str.charAt(i))) {
                return false;
            }
        }
        return true;
    } else {
        return true;
    }
}
public static boolean isNotBlank(String str) {
    return !isBlank(str);
}

From the code we can see: StringUtils.isEmpty(String str) returns true when the string is null or its length is 0. StringUtils.isBlank(String str) returns true when the string is null, empty, or consists only of whitespace characters. StringUtils.isNotEmpty(String str) is equivalent to !isEmpty(str).

Personal Recommendation

I prefer using StringUtils.isBlank(String str) for null‑checking because it covers more cases, especially when validating method parameters.