android tftp实现,在Android中使用TFTP，做工精细出的Andr​​oid，Android的中上挂起SENDFILE...

在Android中使用TFTP可以通过使用第三方库或手动实现TFTP客户端。以下是手动实现TFTP客户端的基本步骤：

1. 创建一个TFTP客户端类，该类将处理TFTP协议的各个步骤。
2. 建立与TFTP服务器的连接，可以使用Socket类实现。
3. 发送RRQ（读请求）或WRQ（写请求）数据包到TFTP服务器，并等待ACK（确认）数据包的响应。
4. 根据ACK数据包的响应，发送或接收数据包，直到传输完成。
5. 关闭与TFTP服务器的连接。

以下是一个简单的TFTP客户端实现示例：

import java.io.*;
import java.net.*;

public class TFTPClient {

    private static final int TFTP_SERVER_PORT = 69;
    private static final int PACKET_SIZE = 512;

    private DatagramSocket socket;
    private InetAddress serverAddress;
    private int serverPort;
    private String fileName;
    private String mode;

    public TFTPClient(String serverAddress, String fileName, String mode) throws UnknownHostException {
        this.serverAddress = InetAddress.getByName(serverAddress);
        this.serverPort = TFTP_SERVER_PORT;
        this.fileName = fileName;
        this.mode = mode;
    }

    public void downloadFile() throws IOException {
        socket = new DatagramSocket();
        socket.setSoTimeout(5000);

        // send read request
        byte[] rrqPacket = createRRQPacket(fileName, mode);
        DatagramPacket rrqPacketToSend = new DatagramPacket(rrqPacket, rrqPacket.length, serverAddress, serverPort);
        socket.send(rrqPacketToSend);

        // receive data
        byte[] fileData = new byte[0];
        int blockNumber = 1;
        while (true) {
            byte[] dataPacket = new byte[PACKET_SIZE + 4];
            DatagramPacket dataPacketToReceive = new DatagramPacket(dataPacket, dataPacket.length);
            socket.receive(dataPacketToReceive);
            if (dataPacket[1] == 5) {
                System.out.println("Error: " + new String(dataPacket, 4, dataPacket.length - 4));
                break;
            } else if (dataPacket[1] == 3) {
                int dataPacketBlockNumber = ((dataPacket[2] & 0xFF) << 8) | (dataPacket[3] & 0xFF);
                if (dataPacketBlockNumber == blockNumber) {
                    byte[] data = new byte[dataPacket.length - 4];
                    System.arraycopy(dataPacket, 4, data, 0, data.length);
                    fileData = concatenateByteArrays(fileData, data);
                    blockNumber++;
                }
                if (dataPacket.length < PACKET_SIZE + 4) {
                    break;
                }
            }
            byte[] ackPacket = createACKPacket(blockNumber - 1);
            DatagramPacket ackPacketToSend = new DatagramPacket(ackPacket, ackPacket.length, serverAddress, serverPort);
            socket.send(ackPacketToSend);
        }

        // write file
        FileOutputStream fos = new FileOutputStream(fileName);
        fos.write(fileData);
        fos.close();

        socket.close();
    }

    private byte[] createRRQPacket(String fileName, String mode) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        baos.write(0);
        baos.write(1);
        baos.write(fileName.getBytes(), 0, fileName.length());
        baos.write(0);
        baos.write(mode.getBytes(), 0, mode.length());
        baos.write(0);
        return baos.toByteArray();
    }

    private byte[] createACKPacket(int blockNumber) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        baos.write(0);
        baos.write(4);
        baos.write((blockNumber >> 8) & 0xFF);
        baos.write(blockNumber & 0xFF);
        return baos.toByteArray();
    }

    private byte[] concatenateByteArrays(byte[] a, byte[] b) {
        byte[] result = new byte[a.length + b.length];
        System.arraycopy(a, 0, result, 0, a.length);
        System.arraycopy(b, 0, result, a.length, b.length);
        return result;
    }
}

要使用此客户端下载文件，只需创建TFTPClient对象并调用downloadFile()方法。例如：

TFTPClient client = new TFTPClient("192.168.1.100", "test.txt", "octet");
client.downloadFile();

这将从TFTP服务器下载test.txt文件并将其保存在当前目录中。