Understanding Apache Commons Lang StringUtils: isEmpty, isBlank, and Related Methods

The article presents the org.apache.commons.lang3.StringUtils class from Apache Commons Lang, a collection of static utilities for handling String and CharSequence values in Java.

isEmpty series

StringUtils.isEmpty() returns true for null or an empty string, but treats a string containing only a space as non‑empty.

StringUtils.isEmpty(null)      = true
StringUtils.isEmpty("")        = true
StringUtils.isEmpty(" ")       = false
StringUtils.isEmpty("bob")     = false
StringUtils.isEmpty(" bob ")  = false

The implementation (since version 3.0) checks for null or zero length:

public static boolean isEmpty(final CharSequence cs) {
    return cs == null || cs.length() == 0;
}

StringUtils.isNotEmpty() simply negates isEmpty() :

public static boolean isNotEmpty(final CharSequence cs) {
    return !isEmpty(cs);
}

StringUtils.isAnyEmpty(...) returns true if any of the supplied CharSequence arguments is empty or null :

StringUtils.isAnyEmpty(null)                = true
StringUtils.isAnyEmpty(null, "foo")        = true
StringUtils.isAnyEmpty("", "bar")         = true
StringUtils.isAnyEmpty("bob", "")         = true
StringUtils.isAnyEmpty(" bob ", null)      = true
StringUtils.isAnyEmpty(" ", "bar")        = false
StringUtils.isAnyEmpty("foo", "bar")     = false

Implementation:

public static boolean isAnyEmpty(final CharSequence... css) {
    if (ArrayUtils.isEmpty(css)) {
        return true;
    }
    for (final CharSequence cs : css) {
        if (isEmpty(cs)) {
            return true;
        }
    }
    return false;
}

StringUtils.isNoneEmpty(...) returns true only when all supplied arguments are non‑empty:

/**
 * Checks if none of the CharSequences are empty ("") or null.
 */
public static boolean isNoneEmpty(final CharSequence... css) {
    // implementation omitted for brevity
}

isBlank series

StringUtils.isBlank() treats null , empty strings, and strings containing only whitespace as blank:

StringUtils.isBlank(null)   = true
StringUtils.isBlank("")     = true
StringUtils.isBlank(" ")    = true
StringUtils.isBlank("bob")  = false
StringUtils.isBlank(" bob ") = false

public static boolean isBlank(final CharSequence cs) {
    int strLen;
    if (cs == null || (strLen = cs.length()) == 0) {
        return true;
    }
    for (int i = 0; i < strLen; i++) {
        if (!Character.isWhitespace(cs.charAt(i))) {
            return false;
        }
    }
    return true;
}

StringUtils.isNotBlank() is the negation of isBlank() :

public static boolean isNotBlank(final CharSequence cs) {
    return !isBlank(cs);
}

StringUtils.isAnyBlank(...) returns true if any argument is blank:

StringUtils.isAnyBlank(null)                = true
StringUtils.isAnyBlank(null, "foo")        = true
StringUtils.isAnyBlank("", "bar")         = true
StringUtils.isAnyBlank("bob", "")         = true
StringUtils.isAnyBlank(" bob ", null)      = true
StringUtils.isAnyBlank(" ", "bar")        = true
StringUtils.isAnyBlank("foo", "bar")     = false

public static boolean isAnyBlank(final CharSequence... css) {
    if (ArrayUtils.isEmpty(css)) {
        return true;
    }
    for (final CharSequence cs : css) {
        if (isBlank(cs)) {
            return true;
        }
    }
    return false;
}

StringUtils.isNoneBlank(...) returns true only when none of the arguments are blank:

public static boolean isNoneBlank(final CharSequence... css) {
    return !isAnyBlank(css);
}

Other StringUtils methods

For a complete list of utilities, refer to the official Apache Commons Lang documentation:

https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html

The article also includes promotional content and QR‑code images for a “Top‑Level Architect” community, but the core technical material focuses on the StringUtils API.