java - 尝试锁定文件进行读取时感到失望

Question

我试图让每个线程读取自己的文本文件。

   private void burden() {

    File mainFolder = new File("C:\\FilesToRead");
    File[] files = mainFolder.listFiles();
    String freeFile;

    for (File file : files) {

        FileChannel channel;
        FileLock lock = null;
        try {
            channel = new RandomAccessFile(file, "r").getChannel();;
            lock = channel.lock();
            // Ok. We get the lock
            readFile(file.getName());

        } catch (OverlappingFileLockException e) {
            continue; // File is open by someone else                 
        } catch (FileNotFoundException f) {

        } catch (IOException ex) {

        } catch (NonWritableChannelException n) {
            System.out.println("NonWritableChannelException");
        } finally {
            try {
                lock.release();
            } catch (IOException ex) {
                System.out.println("IOException!");
            }
        }

    }
} // burden();

我在调试器中得到这张图片:

下一步将把我带到 NonWritableChannelException。

我不明白为什么，因为我试图锁定文件以供读取。

Answer 1

javadoc给出了答案。您使用 .lock()，相当于调用 .lock(0L, Long.MAX_VALUE, false)。

第三个参数，一个 boolean 值，被描述为(强调我的):

true to request a shared lock, in which case this channel must be open for reading (and possibly writing); false to request an exclusive lock, in which case this channel must be open for writing (and possibly reading)

您必须.lock(0L, Long.MAX_VALUE, true)

<小时/>

此外，如果您使用的是 Java 7，请使用 FileChannel.open()