public Collection<File> walkSuitableFiles(int maxNum) {
        Collection<File> suitableFiles = new ArrayList<>();
        walkSuitableFiles(suitableFiles, new File(rootDir), maxNum);
        return suitableFiles;
    }
Research all children files with {@link PathPattern#rootDir} matched whiteList and filtered by blackList.

@param maxNum
@return
inlong-agent/agent-plugins/src/main/java/org/apache/inlong/agent/plugin/task/PathPattern.java