使用 UDP 多播发送文件

Question

我想使用 UDP 多播将我的文件发送给我的朋友，但是当我尝试运行代码时，输出是这样的：

输出：

Exception in thread "main" java.lang.IllegalArgumentException: illegal length or offset
    at java.net.DatagramPacket.setData(Unknown Source)
    at java.net.DatagramPacket.<init>(Unknown Source)
    at Source.createConnection(Source.java:44)
    at Source.main(Source.java:102)

这是我的代码：

 import java.io.*;

    import java.net.*;
    public class Source {
    private DatagramSocket socket = null;
    private FE event = null;
    private String sourceFilePath = "C:/joe's/file/text/hai.txt";
    private String destinationPath = "C:/maria/file2/laboratory/";
    private String hostname= "192.168.43.65";

    public Source(){ }
    public static void main1(String[] args)throws Exception
    {
        try
        {
            DatagramSocket s = new DatagramSocket();

            byte[]line = new byte[100];

            System.out.print("Enter text to send");
            int len = System.in.read(line);
            InetAddress dest = InetAddress.getByName("192.168.43.65");

            DatagramPacket pkt = new DatagramPacket(line,len,dest,16900);

            s.send(pkt);
            s.close();
        }

    catch(Exception err){
        System.err.println(err);

    }
    }

    public void createConnection() {

    try {
    socket = new DatagramSocket();

    byte[] incomingData = new byte[9999];
    event = getFE();
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    ObjectOutputStream os = new ObjectOutputStream(outputStream);
    os.writeObject(event);

    byte[] data = outputStream.toByteArray();
    DatagramPacket sendPacket = new DatagramPacket(data, data.length, 9876);
    socket.send(sendPacket);
    System.out.println("File sent from AppsA");

    DatagramPacket incomingPacket = new DatagramPacket(incomingData, 
    incomingData.length);
    socket.receive(incomingPacket);
    String response = new String(incomingPacket.getData());
    System.out.println("Response from AppsB:" + response);
    Thread.sleep(2000);
    System.exit(0); 
    }

 catch (UnknownHostException e) {
    e.printStackTrace();
    } catch (SocketException e) {
    e.printStackTrace();
    } catch (IOException e) {
    e.printStackTrace();
    } catch (InterruptedException e) {
    e.printStackTrace();
    }
    }



 public FE getFE() {
 FE fileEvent = new FE();
 String fileName = sourceFilePath.substring(sourceFilePath.lastIndexOf("/") + 1, 
 sourceFilePath.length());
 String path = sourceFilePath.substring(0, sourceFilePath.lastIndexOf("/") + 1);
    fileEvent.setDestinationDirectory(destinationPath);

    fileEvent.setFilename(fileName);
    fileEvent.setSourceDirectory(sourceFilePath);
    File file = new File(sourceFilePath);
    if (file.isFile())
 {
    try {
    DataInputStream diStream = new DataInputStream(new FileInputStream(file));
    long len = (int) file.length();
    byte[] fileBytes = new byte[(int) len];
    int read = 0;
    int numRead = 0;
    while (read < fileBytes.length && (numRead = diStream.read(fileBytes, read,
    fileBytes.length - read)) >= 0) {
    read = read + numRead;
    }

    fileEvent.setFileSize(len);
    fileEvent.setFileData(fileBytes);
    fileEvent.setStatus("Success");
    } catch (Exception e) {
    e.printStackTrace();
    fileEvent.setStatus("Error");
    }
    }

 else {
    System.out.println("path specified is not pointing to a file");
    fileEvent.setStatus("Error");
    }
    return fileEvent;
    }
    public static void main(String[] args)throws Exception {
    Source app = new Source();
    app.createConnection();
    }
    }

Answer 1

你的问题在于DatagramPacket的构造函数使用不当：

DatagramPacket sendPacket = new DatagramPacket(data, data.length, 9876);

上面一行是正确的，但是下面的代码：

DatagramPacket incomingPacket = new DatagramPacket(incomingData, 
incomingData.length);

应该是这样的：

DatagramPacket incomingPacket = new DatagramPacket(incomingData, 
9876);

DatagramPacket 构造函数中的第二个参数是长度。您最初将 sendPacket 上的长度设置为 9876

使用 UDP 多播发送文件

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