liquibase-core/src/main/java/liquibase/util/file/FilenameUtils.java
private static String doGetFullPath(String filename, boolean includeSeparator) {
        if (filename == null) {
            return null;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        if (prefix >= filename.length()) {
            if (includeSeparator) {
                return getPrefix(filename);  // add end slash if necessary
            } else {
                return filename;
            }
        }
        int index = indexOfLastSeparator(filename);
        if (index < 0) {
            return filename.substring(0, prefix);
        }
        int end = index + (includeSeparator ?  1 : 0);
        return filename.substring(0, end);
    }
private static String doGetFullPath(String filename, boolean includeSeparator) {
        if (filename == null) {
            return null;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        if (prefix >= filename.length()) {
            if (includeSeparator) {
                return getPrefix(filename);  // add end slash if necessary
            } else {
                return filename;
            }
        }
        int index = indexOfLastSeparator(filename);
        if (index < 0) {
            return filename.substring(0, prefix);
        }
        int end = index + (includeSeparator ?  1 : 0);
        return filename.substring(0, end);
    }
Does the work of getting the path.

@param filename  the filename
@param includeSeparator  true to include the end separator
@return the path