java - Java的BufferunderflowException

Question

我正在将值写入文件。

值写正确。在另一个应用程序中，我可以毫无异常(exception)地读取文件。

但是在我的新应用程序中，尝试读取文件时收到了Bufferunderflowexception。

我花了几天的时间来解决这个问题，但我只是不知道如何解决。

也做了很多研究。
bufferunderflowexception指的是:

Double X1 = mappedByteBufferOut.getDouble(); //8 byte (double)

这是我读取文件的代码:

 @Override
    public void paintComponent(Graphics g) {

    RandomAccessFile randomAccessFile = null;
    MappedByteBuffer mappedByteBufferOut = null;
    FileChannel fileChannel = null;

    try {
        super.paintComponent(g);

        File file = new File("/home/user/Desktop/File");

        randomAccessFile = new RandomAccessFile(file, "r");

        fileChannel = randomAccessFile.getChannel();

        mappedByteBufferOut = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, randomAccessFile.length());

        while (mappedByteBufferOut.hasRemaining()) {

            Double X1 = mappedByteBufferOut.getDouble(); //8 byte (double)
            Double Y1 = mappedByteBufferOut.getDouble();
            Double X2 = mappedByteBufferOut.getDouble();
            Double Y2 = mappedByteBufferOut.getDouble();
            int colorRGB = mappedByteBufferOut.getInt(); //4 byte (int)
            Color c = new Color(colorRGB);

            Edge edge = new Edge(X1, Y1, X2, Y2, c);

            listEdges.add(edge);

        }
        repaint();

        for (Edge ed : listEdges) {
            g.setColor(ed.color);
            ed = KochFrame.edgeAfterZoomAndDrag(ed);
            g.drawLine((int) ed.X1, (int) ed.Y1, (int) ed.X2, (int) ed.Y2);
        }
    }
    catch (IOException ex)
    {
        System.out.println(ex.getMessage());
    }
    finally
    {
        try
        {
            mappedByteBufferOut.force();
            fileChannel.close();
            randomAccessFile.close();
            listEdges.clear();
        } catch (IOException ex)
        {
            System.out.println(ex.getMessage());
        }
    }
}

我希望有一个人可以帮助我。

Answer 1

从java.nio.ByteBuffer的docs中:

Throws: BufferUnderflowException - If there are fewer than eight bytes remaining in this buffer

我认为这很清楚这是异常的来源。为了修复它，您需要确保ByteBuffer中有足够的数据以便读取double(8个字节)，而不是hasRemaining()，后者仅检查一个字节:

while (mappedByteBufferOut.remaining() >= 36) {//36 = 4 * 8(double) + 1 * 4(int)