阻塞佇列的使用：

public class FileCrawler implements Runnable {
    private final BlockingQueue<File> fileQueue = new LinkedBlockingQueue<>(10);
    final List<String> result = new ArrayList<>(16);
    private final FileFilter filter;
    private final String root;
    volatile
 
 boolean running = true;
    private Indexer indexer;

    public FileCrawler(FileFilter filter, String root) {
        this.filter = filter;
        this.root = root;
        indexer = new Indexer("Indexer");
    }

    @Override
    public void run() {
        File src = new File(root);
        if
 
 (src.exists()) {
            try {
                indexer.start();
                cralw(src);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
        running = false;
    }

    private void cralw(File src) throws InterruptedException {
        File[] files = src.listFiles();
        if
 
 (files != null)
            for (File file : files) {
                if (file.isDirectory())
                    cralw(file);
                else if (filter.accept(file))
                    fileQueue.put(file);
            }
    }

    private class Indexer extends Thread {
        public Indexer(String name) {
            super(name);
        }

        @Override
        public void run() {
            while (running || !fileQueue.isEmpty()) {
                try {
                    indexFile(fileQueue.take());
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
            showResult();
        }

        private void indexFile(File take) {
            LineNumberReader in = null;
            try {
                in = new LineNumberReader(new FileReader(take));
                String line;
                while ((line = in.readLine()) != null) {
                    if (line.contains("it")) {
                        addResult(in, take, line);
                    }
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        private void addResult(LineNumberReader in, File src, String line) {
            StringBuilder msg = new StringBuilder();
            String path = src.getAbsolutePath();
            msg.append("path : " + path + " ; ");
            msg.append("lineNumber : " + in.getLineNumber() + " ; ");
            msg.append("line : " + line);
            result.add(msg.toString());
        }

    }

    public void showResult() {
        for (String str : result) {
            System.out.println(str);
        }
    }

}

呼叫

public class TestFindTxt {
    public static void main(String[] args) {
        FileFilter filter = new FileFilter() {
            @Override
            public boolean accept(File pathname) {
                return pathname.isFile() && pathname.getName().endsWith(".txt");
            }
        };
        String root = "g:/a";
        FileCrawler crawler = new FileCrawler(filter, root);
        new Thread(crawler).start();
    }
}

結果：