Java使用ymodem传输

Java可以使用YModem协议进行文件传输，以下是一个基本的示例代码：

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

public class YModem {
    private static final int PACKET_SIZE = 1024;
    private static final int FILE_SIZE = 1024 * 1024;

    private static final byte SOH = 0x01;
    private static final byte STX = 0x02;
    private static final byte EOT = 0x04;
    private static final byte ACK = 0x06;
    private static final byte NAK = 0x15;
    private static final byte CAN = 0x18;

    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            System.err.println("Usage: java YModem <filename> <port>");
            System.exit(1);
        }
        String filename = args[0];
        String portName = args[1];

        try (RandomAccessFile file = new RandomAccessFile(filename, "r");
             SerialPort port = new SerialPort(portName)) {

            // send file name and size
            sendFileNameAndSize(port, filename, (int) file.length());

            // send file data
            sendFileData(port, file);

            // end of transmission
            sendEOT(port);
        }
    }

    private static void sendFileNameAndSize(SerialPort port, String filename, int fileSize) throws Exception {
        // send file name
        byte[] nameBytes = filename.getBytes();
        port.write(nameBytes);
        port.write(0);

        // send file size
        String fileSizeStr = String.format("%d", fileSize);
        byte[] sizeBytes = fileSizeStr.getBytes();
        port.write(sizeBytes);
        port.write(0);
    }

    private static void sendFileData(SerialPort port, RandomAccessFile file) throws Exception {
        byte[] buffer = new byte[PACKET_SIZE];
        int bytesRead;
        int blockNumber = 1;

        while ((bytesRead = file.read(buffer)) != -1) {
            sendPacket(port, blockNumber, buffer, bytesRead);
            blockNumber++;
        }
    }

    private static void sendPacket(SerialPort port, int blockNumber, byte[] data, int length) throws Exception {
        byte packetNumber = (byte) blockNumber;
        byte packetNumberComplement = (byte) ~blockNumber;

        // send packet header
        if (length == PACKET_SIZE) {
            port.write(STX);
        } else {
            port.write(SOH);
        }
        port.write(packetNumber);
        port.write(packetNumberComplement);

        // send packet data
        port.write(data, 0, length);
        int paddingLength = PACKET_SIZE - length;
        for (int i = 0; i < paddingLength; i++) {
            port.write(0);
        }

        // wait for ACK or NAK
        byte response = port.read();
        if (response == ACK) {
            // packet successfully received
            return;
        } else if (response == NAK) {
            // packet not received, resend
            sendPacket(port, blockNumber, data, length);
        } else if (response == CAN) {
            // transmission cancelled
            throw new Exception("Transmission cancelled");
        } else {
            // unknown response
            throw new Exception("Unknown response: " + response);
        }
    }

    private static void sendEOT(SerialPort port) throws Exception {
        // send EOT
        port.write(EOT);

        // wait for ACK
        byte response = port.read();
        if (response != ACK) {
            throw new Exception("Unknown response: " + response);
        }
    }
}

注意，此示例代码仅用于演示目的，实际使用中需要根据具体需求进行修改和完善。同时，还需要使用相应的串口库（如 RXTX）来连接串口设备。