public static String stripStart(String str, String stripChars) {
        int strLen;
        if (str == null || (strLen = str.length()) == 0) {
            return str;
        }
        int start = 0;
        if (stripChars == null) {
            while (start != strLen && Character.isWhitespace(str.charAt(start))) {
                start++;
            }
        } else if (stripChars.length() == 0) {
            return str;
        } else {
            while (start != strLen && stripChars.indexOf(str.charAt(start)) != INDEX_NOT_FOUND) {
                start++;
            }
        }
        return str.substring(start);
    }
<p>Strips any of a set of characters from the start of a String.</p>

<p>A {@code null} input String returns {@code null}.
An empty string ("") input returns the empty string.</p>

<p>If the stripChars String is {@code null}, whitespace is
stripped as defined by {@link Character#isWhitespace(char)}.</p>

<pre>
StringUtils.stripStart(null, *)          = null
StringUtils.stripStart("", *)            = ""
StringUtils.stripStart("abc", "")        = "abc"
StringUtils.stripStart("abc", null)      = "abc"
StringUtils.stripStart("  abc", null)    = "abc"
StringUtils.stripStart("abc  ", null)    = "abc  "
StringUtils.stripStart(" abc ", null)    = "abc "
StringUtils.stripStart("yxabc  ", "xyz") = "abc  "
</pre>

@param str  the String to remove characters from, may be null
@param stripChars  the characters to remove, null treated as whitespace
@return the stripped String, {@code null} if null String input
android/android_framework/base/src/main/java/lang3/StringUtils.java