Java通过FIO读取文件

Question

我正在制作一个TFTP应用程序。根据RFC协议，所有数据必须以最大大小为512字节的块的形式发送。因此每个分组可以是<= 512字节。

奇怪的是，对于UDP协议，每次高达3mb的传输都没有大的损失。唯一可能发生的损失是当文件的最后一个块被读取时小于512个字节。

private void sendData() throws Exception
{
    DatagramPacket data = new DatagramPacket(outgoingData, outgoingData.length, clientAddress, clientPort);
    InputStream fis = new FileInputStream(responseData);

    int a;
    while((a = fis.read(outgoingData,0,512)) != -1)
    {
        serverSocket.send(data);
        Thread.sleep(5);
    }
}

由于这是一个关于读取文件的问题，我如何修复文件末尾的丢失以及无法读取小于512的文件的问题

客户端：

private void receiveData() throws Exception
{
    DatagramPacket receiveData = new DatagramPacket(incomingData, incomingData.length);
    OutputStream fos = new FileOutputStream(new File("1"+data));
    while(true)
    {
        clientSocket.receive(receiveData);
        if(receiveData.getLength() == 512)
        {
            fos.write(incomingData);xx
        } else {
            fos.write(incomingData);
            fos.close();
            break;
        }
    }
    clientSocket.close();
}

Answer 1

您的数据包(data)具有固定长度的outgoingData.length (512?)现在就来。因此，当您调用serverSocket.send(data)时，它会发送outgoingData数组中的所有数据。

问题是fis.read(outgoingData, 0, 512)有时读取的数据少于512字节。这很可能发生在文件输入流的末尾，此时根本没有那么多数据可供读取。但它也可能发生得更早(在实践中不太可能，但您仍然应该检查以确保安全)。

您已经在a中存储了实际读取的字节数。只需将这个数字传递给setLength，这样DatagramSocket就会知道只发送这么多数据。

这应该能起到作用：

private void sendData() throws Exception
{
    DatagramPacket data = new DatagramPacket(outgoingData, outgoingData.length, clientAddress, clientPort);
    InputStream fis = new FileInputStream(responseData);

    int a;
    while((a = fis.read(outgoingData,0,512)) != -1)
    {
        data.setLength(a);
        // or this
        //data = new DatagramPacket(outgoingData, a, clientAddress, clientPort);

        serverSocket.send(data);
        Thread.sleep(5);
    }
}

接收：

private void receiveData() throws Exception {
    DatagramPacket receiveData = new DatagramPacket(new byte[512], 512);
    OutputStream fos = new FileOutputStream(new File("1"+data));
    while (true) {
        clientSocket.receive(receiveData);
        if (receiveData.getLength() == 512) {
            fos.write(receiveData.getData());
        } else {
            fos.write(receiveData.getData(), receiveData.getOffset(), receiveData.getLength());
            break;
        }
    }
    fos.close();
    clientSocket.close();
}

Answer 2

    private void sendData() throws Exception
{
    DatagramPacket data = new DatagramPacket(outgoingData, outgoingData.length, clientAddress, clientPort);
    InputStream fis = new FileInputStream(responseData);

    int a;
    while((a = fis.read(outgoingData,0,512)) != -1)
    {
        data.setLength(a); //'a' is the number of bytes read setLength(int) lets you set the length of bytes you want to sent
        serverSocket.send(data);
        Thread.sleep(5);
    }
}

setLength(int) Method DatagramPacket现在在接收端，你可以这样做：

byte[]buffer = new byte[512];
DatagramPacket packet = new DatagramPacket(buffer,buffer.length);
while(socket.isBound() && !socket.isClosed()){
    socket.receive(packet);
    system.out.println("Packet Length: "+packet.getLength());
    //code here
}

修复: Server.java中的

private void sendResponse(String res) throws Exception
        {
            if(res.equals("Y"))
            {
                // Send ACK -> Send File
                DatagramPacket x = new DatagramPacket(outgoingData, outgoingData.length, clientAddress, clientPort);
                serverSocket.send(x); //<<SEND ACK
                sendData();
            } else {
                String error = "ERROR: The file you requested does not exist.";
                outgoingData = error.getBytes();
                DatagramPacket err = new DatagramPacket(outgoingData, outgoingData.length, clientAddress, clientPort);

                serverSocket.send(err);
            }
        }

我注意到你没有发送ack，而客户正在期待它，这似乎是你唯一的问题。第一个包目前对您没有任何帮助。现在，您只需将ack包设置为您想要的。我只是在它不包含字符串"ERROR“的时候发送了它。