java 采用 Ymodem传输文件

Java可以使用串口通讯库来实现Ymodem传输文件。以下是一个简单的示例代码：

import java.io.*;
import java.util.*;

import purejavacomm.*;

public class YModem {
    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;
    private static final byte CRC16 = 0x43;

    private static final int BLOCK_SIZE = 1024;
    private static final int MAX_RETRIES = 10;

    private static final int FILE_SIZE_OFFSET = 132;
    private static final int FILE_SIZE_LENGTH = 10;
    private static final int FILE_NAME_OFFSET = 0;
    private static final int FILE_NAME_LENGTH = 128;

    public static void send(String fileName, OutputStream outputStream) throws Exception {
        File file = new File(fileName);
        FileInputStream fileInputStream = new FileInputStream(file);
        long fileSize = file.length();

        byte[] fileNameBytes = Arrays.copyOf(file.getName().getBytes("ASCII"), FILE_NAME_LENGTH);
        byte[] fileSizeBytes = Arrays.copyOf(Long.toString(fileSize).getBytes("ASCII"), FILE_SIZE_LENGTH);

        int blockNumber = 1;
        int retries = 0;

        while (true) {
            outputStream.write(NAK);

            int bytesRead = fileInputStream.read();
            if (bytesRead != SOH) {
                throw new Exception("Invalid start of header");
            }

            int blockIndex = 0;
            byte[] block = new byte[BLOCK_SIZE + 4];
            block[blockIndex++] = SOH;
            block[blockIndex++] = (byte) blockNumber;
            block[blockIndex++] = (byte) ~blockNumber;

            bytesRead = fileInputStream.read(block, blockIndex, BLOCK_SIZE);
            if (bytesRead < BLOCK_SIZE) {
                Arrays.fill(block, blockIndex + bytesRead, blockIndex + BLOCK_SIZE, (byte) 0x1A);
            }

            int crc = calculateCRC16(block, 3, BLOCK_SIZE);
            block[blockIndex + BLOCK_SIZE] = (byte) ((crc >> 8) & 0xFF);
            block[blockIndex + BLOCK_SIZE + 1] = (byte) (crc & 0xFF);

            outputStream.write(block);

            int response = readByte(inputStream);
            if (response == ACK) {
                blockNumber++;
                if (blockNumber == 256) {
                    blockNumber = 0;
                }
                retries = 0;
                if (bytesRead < BLOCK_SIZE) {
                    break;
                }
            } else if (response == NAK) {
                retries++;
                if (retries >= MAX_RETRIES) {
                    throw new Exception("Transfer failed");
                }
            } else {
                throw new Exception("Invalid response: " + response);
            }
        }

        fileInputStream.close();

        while (true) {
            outputStream.write(EOT);
            int response = readByte(inputStream);
            if (response == NAK) {
                continue;
            } else if (response == ACK) {
                break;
            } else {
                throw new Exception("Invalid response: " + response);
            }
        }
    }

    public static void receive(String fileName, InputStream inputStream) throws Exception {
        FileOutputStream fileOutputStream = new FileOutputStream(fileName);

        byte[] block = new byte[BLOCK_SIZE + 4];
        int blockNumber = 1;
        int retries = 0;
        boolean endOfFile = false;

        while (!endOfFile) {
            block[0] = (byte) inputStream.read();
            if (block[0] == EOT) {
                outputStream.write(ACK);
                break;
            } else if (block[0] != SOH && block[0] != STX) {
                throw new Exception("Invalid start of header");
            }

            int bytesRead = inputStream.read(block, 1, BLOCK_SIZE + 3);
            if (bytesRead < BLOCK_SIZE + 3) {
                throw new Exception("Invalid block size");
            }

            int crc = calculateCRC16(block, 3, BLOCK_SIZE);
            if (crc != ((block[BLOCK_SIZE + 3] << 8) | (block[BLOCK_SIZE + 2] & 0xFF))) {
                throw new Exception("Invalid CRC");
            }

            if (blockNumber == block[1] && ~blockNumber == block[2]) {
                retries = 0;
                fileOutputStream.write(block, 3, BLOCK_SIZE);
                outputStream.write(ACK);
                blockNumber++;
                if (blockNumber == 256) {
                    blockNumber = 0;
                }
            } else if (blockNumber == ((block[1] + 1) & 0xFF) && ~(blockNumber) == block[2]) {
                retries = 0;
                endOfFile = true;
                int bytesToWrite = 0;
                for (int i = 0; i < FILE_SIZE_LENGTH; i++) {
                    if (fileSizeBytes[i] == 0) {
                        break;
                    }
                    bytesToWrite = bytesToWrite * 10 + (fileSizeBytes[i] - '0');
                }
                fileOutputStream.write(block, 3, bytesToWrite);
                outputStream.write(ACK);
            } else {
                retries++;
                if (retries >= MAX_RETRIES) {
                    throw new Exception("Transfer failed");
                }
                outputStream.write(NAK);
            }
        }

        fileOutputStream.close();
    }

    private static int calculateCRC16(byte[] data, int offset, int length) {
        int crc = 0;
        for (int i = offset; i < offset + length; i++) {
            crc ^= (data[i] & 0xFF) << 8;
            for (int j = 0; j < 8; j++) {
                if ((crc & 0x8000) != 0) {
                    crc = (crc << 1) ^ 0x1021;
                } else {
                    crc <<= 1;
                }
            }
        }
        return crc & 0xFFFF;
    }

    private static int readByte(InputStream inputStream) throws Exception {
        long startTime = System.currentTimeMillis();
        while (inputStream.available() == 0) {
            if (System.currentTimeMillis() - startTime > 10000) {
                throw new Exception("Timeout waiting for response");
            }
        }
        return inputStream.read();
    }
}

在这个示例代码中，send()方法用于发送文件，而receive()方法用于接收文件。如果您使用的是Windows系统，则需要安装Java Communications API（JavaComm）来使用串口通讯库。