java ymodem

Ymodem 是一种用于在串行通信中进行文件传输的协议。在 Java 中实现 Ymodem 文件传输可以使用以下步骤：

1. 建立串行通信连接：使用 Java 的串行通信库（如 RXTX）来建立与目标设备的串行通信连接。

2. 实现 Ymodem 协议：在 Java 中实现 Ymodem 协议的核心功能，包括发送文件和接收文件。这涉及到处理 Ymodem 协议的数据包格式、校验和和重传机制等。

3. 发送文件：通过串行连接发送文件，将文件分成多个数据包并使用 Ymodem 协议进行传输。发送过程中需要处理接收方的确认和重传请求。

4. 接收文件：通过串行连接接收文件，解析接收到的数据包并按照 Ymodem 协议进行处理。在接收过程中需要发送确认和重传请求。

需要注意的是，实现 Ymodem 文件传输可能涉及到一些底层的串行通信和字节处理的知识。你可以参考相关的文档和示例代码来帮助你完成这个任务。

相关问题

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。

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。