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

Hello everyone, I am Peng Lei.

New colleagues who have been working with Java for three years may not know the difference between isEmpty and isBlank , or even the existence of methods such as isAnyEmpty , isNoneEmpty , isAnyBlank , and isNoneBlank . Let's explore the org.apache.commons.lang3.StringUtils utility class.

isEmpty Series

StringUtils.isEmpty()

Checks whether a CharSequence is null or has a length of zero. A string containing only a space character is not considered empty.

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

/**
 * NOTE: This method changed in Lang version 2.0.
 * It no longer trims the CharSequence.
 * That functionality is available in isBlank().
 *
 * @param cs the CharSequence to check, may be null
 * @return {@code true} if the CharSequence is empty or null
 * @since 3.0 Changed signature from isEmpty(String) to isEmpty(CharSequence)
 */
public static boolean isEmpty(final CharSequence cs) {
    return cs == null || cs.length() == 0;
}

StringUtils.isNotEmpty()

Returns the opposite of isEmpty() , i.e., !isEmpty(cs) .

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

StringUtils.isAnyEmpty()

Returns true if any of the supplied CharSequence arguments is null or empty.

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

/**
 * @param css the CharSequences to check, may be null or empty
 * @return {@code true} if any of the CharSequences are empty or null
 * @since 3.2
 */
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()

Equivalent to !isAnyEmpty(css) ; returns true only when **all** supplied CharSequences are non‑null and non‑empty.

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

/**
 * @param css the CharSequences to check, may be null or empty
 * @return {@code true} if none of the CharSequences are empty or null
 * @since 3.2
 */
public static boolean isNoneEmpty(final CharSequence... css) {
    return !isAnyEmpty(css);
}

isBlank Series

StringUtils.isBlank()

Checks whether a CharSequence is null , empty ( "" ) or contains only whitespace characters.

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

/**
 * @param cs the CharSequence to check, may be null
 * @return {@code true} if the CharSequence is null, empty or whitespace only
 * @since 2.0
 * @since 3.0 Changed signature from isBlank(String) to isBlank(CharSequence)
 */
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()

Returns the opposite of isBlank() , i.e., !isBlank(cs) .

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

StringUtils.isAnyBlank()

Returns true if any of the supplied CharSequences is null , empty, or consists solely of whitespace.

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

/**
 * @param css the CharSequences to check, may be null or empty
 * @return {@code true} if any of the CharSequences are blank, null or whitespace only
 * @since 3.2
 */
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 **all** supplied CharSequences are non‑null, non‑empty and contain at least one non‑whitespace character.

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

/**
 * @param css the CharSequences to check, may be null or empty
 * @return {@code true} if none of the CharSequences are blank, null or whitespace only
 * @since 3.2
 */
public static boolean isNoneBlank(final CharSequence... css) {
    return !isAnyBlank(css);
}

Other StringUtils Methods

For a complete list of methods and detailed documentation, refer to the official Apache Commons Lang API:

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

Additional illustrative images are included in the original article.