long getSourceFileLength(Metadata m) {
        String lenString = m.get(Metadata.CONTENT_LENGTH);
        if (lenString == null) {
            return NON_EXISTENT_FILE_LENGTH;
        }
        try {
            return Long.parseLong(lenString);
        } catch (NumberFormatException e) {
            //swallow
        }
        return NON_EXISTENT_FILE_LENGTH;
    }
@param extractRootDir
@param relativeSourceFilePath
@return extractFile or null if couldn't find one.
tika-eval/tika-eval-app/src/main/java/org/apache/tika/eval/app/AbstractProfiler.java