使用java语言的tftp代码调用

在Java中实现TFTP（简单文件传输协议）客户端通常需要使用到网络编程的知识。以下是一个简单的TFTP客户端代码示例，它使用了Java的`DatagramSocket`和`DatagramPacket`类来实现。

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

public class TFTPClient {

    private static final int TFTPD_PORT = 69; // TFTP服务端默认端口号

    public static void main(String[] args) {
        if (args.length != 2) {
            System.out.println("Usage: java TFTPClient <hostname> <filename>");
            return;
        }

        String hostname = args[0];
        String filename = args[1];

        DatagramSocket clientSocket = null;
        try {
            clientSocket = new DatagramSocket();

            // 发送读取请求
            byte[] opcode = {'1', '0'}; // RRQ opcode
            byte[] filenameData = filename.getBytes();
            byte[] mode = "octet".getBytes();

            byte[] buffer = new byte[516];
            int offset = 0;

            // 构建RRQ包
            buffer[offset++] = opcode[0];
            buffer[offset++] = opcode[1];
            System.arraycopy(filenameData, 0, buffer, offset, filenameData.length);
            offset += filenameData.length;
            System.arraycopy(mode, 0, buffer, offset, mode.length);

            // 发送请求到服务器
            InetAddress serverAddress = InetAddress.getByName(hostname);
            DatagramPacket request = new DatagramPacket(buffer, buffer.length, serverAddress, TFTPD_PORT);
            clientSocket.send(request);

            // 接收响应
            byte[] receiveData = new byte[516];
            DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
            clientSocket.receive(receivePacket);
            int errorCode = receiveData[1] * 256 + receiveData[2];

            if (errorCode != 0) {
                System.out.println("Error: " + errorCode);
                return;
            }

            // 读取数据
            int fileLength = (receiveData[4] << 24) + (receiveData[5] << 16) + (receiveData[6] << 8) + receiveData[7];
            byte[] fileData = new byte[fileLength];
            System.arraycopy(receiveData, 8, fileData, 0, fileLength);
            FileOutputStream out = new FileOutputStream(filename);

            // 循环直到文件传输完毕
            while (fileLength > 0) {
                int length = Math.min(fileLength, receiveData.length - 8);
                System.arraycopy(receiveData, 8, fileData, fileLength - fileLength, length);
                out.write(fileData, fileLength - fileLength, length);
                fileLength -= length;

                clientSocket.receive(receivePacket);
                System.arraycopy(receiveData, 8, fileData, fileLength - fileLength, length);
            }

            out.close();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (clientSocket != null) {
                clientSocket.close();
            }
        }
    }
}

这段代码展示了如何使用Java创建一个简单的TFTP客户端，它尝试从指定的主机读取一个文件。客户端首先发送一个读取请求（RRQ），然后接收服务器的响应。如果响应是错误码，它将打印错误信息；如果成功，它将进入循环接收文件数据直到整个文件传输完成。

请注意，这个示例是一个非常基础的TFTP客户端实现，并没有处理所有的TFTP协议细节和网络异常情况。在实际应用中，可能需要更健壮的错误处理和协议支持。