java - 安卓 : nonwritablechannelException and ClosedChannelException

Question

我正在使用FileLock，但不知道为什么总是遇到nonwritablechannelException异常:

public static List<String> readFromFile(Context ctx, String filename) {
        try {
            FileInputStream fis = ctx.openFileInput(filename);
            // lock this file
            FileLock lock = fis.getChannel().tryLock(); // Exception here
            // unlock this file
            lock.release();
            return null;
        } catch (Exception e) {
            Log.i(TAG, "Cannot read file");
            e.printStackTrace();
        }
        return null;
}

当我从文件写入时遇到另一个异常:Exception ClosedChannelException

public static boolean saveToFile(Context ctx, List<String> lst, String filename) {
        try {
            FileOutputStream fos = ctx.openFileOutput(filename, Context.MODE_PRIVATE);
            // lock this file
            FileLock lock = fos.getChannel().lock();
            PackageObject obj = new PackageObject(lst);
            ObjectOutputStream writer = new ObjectOutputStream(fos);
            writer.writeObject(obj);
            writer.close();
            // unlock this file
            lock.release(); // Exception at this line
                fos.close();
            return true;
        } catch (Exception e) {
            Log.i(TAG, "Cannot write file");
            e.printStackTrace();
        }
        return false;
    }

在 Android 开发者页面上，他们解释这个异常是:

A NonWritableChannelException is thrown when attempting to write to a channel that is not open for writing.

但我仍然无法解释为什么。请帮我弄清楚为什么我会遇到这个异常(exception)。

谢谢:)

Answer 1

"A NonWritableChannelException is thrown when attempting to write to a channel that is not open for writing."

您使用 openFileInput 打开了文件/ channel ...打开它是为了读取而不是写入。如果你想锁定文件，你必须使用 openFileOutput 打开它进行写入......或者也可以。