我们的老师让我们修改 MulticastImageSender (MIS) 和 MulticastImageReceiver (MIR) 类中的两个程序。唯一的问题是，我似乎无法弄清楚如何让它们像他给我们时那样正常工作。我一直被告知我的地址不是多播地址。
MIS 的参数：java -jar MIS.jar 127.0.0.0 1234 4 "/home/kevin/Pictures/ME.png" MIR 的参数：java -jar MIR.jar 127.0.0.0 1234
然后我先运行接收器，但我不断得到这些输出
MIS 的输出：
Sent /home/kevin/Pictures/ME.png to 127.0.0.0 on port 1234
MIR 的输出：
Exception in thread "main" java.lang.IllegalArgumentException: Not a multicast address
at MulticastImageReceiver.main(MulticastImageReceiver.java:35)
现在我知道多播地址是 244.xxx 并保留了一些地址，但我想我需要使用本地机器地址将其发送给自己。或者通过使用 244.xxx 地址创建我的多播套接字，我的路由器（计算机网络接口卡？）知道我的地址是 127.0.0.0，并且发送者使用相同的路由器（NIC？）创建多播套接字知道发送它又给我了？
** 我曾经发布过这个问题，但无济于事。我意识到我收到的错误来自这一行
if (!multicastAddress.isMulticastAddress())
我只是在学习所有这些东西，并试图弄清楚如何实际运行这个程序，以便我可以真正开始我的任务。我所需要的只是快速解释要使用的地址和原因。
使用 Ubuntu Oneric、Eclipse IDE、Java
资源：
MIS
public class MulticastImageSender
{
private static final int TIMEOUT = 3000; // Time between sends (milliseconds)
private static final int MAXFILELEN = 65000; // File must fit in single datagram
public static void main(String[] args) throws IOException, InterruptedException
{
if (args.length < 4) // Test for correct # of args
throw new IllegalArgumentException("Parameter(s): <Multicast Address> <Port> <TTL> <Image File> [<Image File>...]");
InetAddress multicastAddress = InetAddress.getByName(args[0]);
int destPort = Integer.parseInt(args[1]);
// Destination port of multicast packets
int TTL = Integer.parseInt(args[2]);
// Create a UDP multicast socket with any available local port
MulticastSocket socket = new MulticastSocket();
socket.setTimeToLive(TTL);
// Set the TTL
for (int i=3; i < args.length; i++)
{
RandomAccessFile file = new RandomAccessFile(args[i], "r");
if (file.length() > MAXFILELEN)
throw new IOException("File too big");
byte [] fileBuffer = new byte[(int) file.length()];
file.read(fileBuffer);
file.close();
// Create a datagram to send
DatagramPacket sendPacket = new DatagramPacket(fileBuffer, fileBuffer.length, multicastAddress, destPort);
socket.send(sendPacket); // Send the echo string
System.out.println("Sent " + args[i] + " to " + sendPacket.getAddress().getHostAddress() + " on port " + sendPacket.getPort());
Thread.sleep(TIMEOUT);
}
socket.close();
}
}
MIR 及其支持线程
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.io.*;
public class MulticastImageReceiver extends JFrame
{
private static final long serialVersionUID = 1L;
private JLabel picture;
// Label to contain image
public MulticastImageReceiver()
{
super("Multicast Image Receiver"); // Set the window title
setSize(300, 300);
// Set the window size
picture = new JLabel("No image", SwingConstants.CENTER);
JScrollPane scrollPane = new JScrollPane(picture);
getContentPane().add(scrollPane, "Center");
addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent evt){ System.exit(0);}});
}
public JLabel getPicture()
{
return picture;
}
public static void main(String[] args) throws IOException
{
if (args.length != 2) // Test for correct # of args
throw new IllegalArgumentException( "Parameter(s): <Multicast Address> <Port>");
final InetAddress multicastAddress = InetAddress.getByName(args[0]);
if (!multicastAddress.isMulticastAddress())
throw new IllegalArgumentException("Not a multicast address");
int port = Integer.parseInt(args[1]);
// Destination port of multicast packets
MulticastImageReceiver multicastImageReceiver = new MulticastImageReceiver();
multicastImageReceiver.setVisible(true);
new Thread(new MulticastImageReceiverThread(multicastImageReceiver, multicastAddress, port,"No Image")).start();
}
}
米尔螺纹
import java.awt.*;
import javax.swing.*;
import java.net.*;
import java.io.*;
class MulticastImageReceiverThread implements Runnable
{
private static final int MAXFILELEN = 65000;
// File must fit in single datagram
private InetAddress multicastAddress;
// Sender multicast address
private int port;
// Sender port
Runnable updateImage;
// Anonymous class for Swing event queue to update label
String imageText;
// Label text
byte[] image = new byte[MAXFILELEN];
// Bytes of image
boolean imageValid = false;
// True if image contains valid bytes
public MulticastImageReceiverThread(final MulticastImageReceiver frame, InetAddress multicastAddress, int port, String initialImageText)
{
this.multicastAddress = multicastAddress;
this.port = port;
this.imageText = initialImageText;
updateImage = new Runnable()
{
public void run()
{
JLabel picture = frame.getPicture();
picture.setText(imageText);
if (imageValid)
{
ImageIcon newImage = new ImageIcon(image);
picture.setIcon(newImage);
picture.setPreferredSize(new Dimension(newImage.getIconWidth(), newImage.getIconHeight()));
}
else
picture.setIcon(null);
picture.revalidate();
}
};
}
public void changeImage()
{
try
{
SwingUtilities.invokeAndWait(updateImage);
// Put update in queue and wait until handled
}
catch (Exception e)
{
System.out.println(e.getMessage());}
}
public void run()
{
// Create a datagram to receive
DatagramPacket recvPacket = new DatagramPacket(image, MAXFILELEN);
MulticastSocket socket;
// Create a UDP multicast socket with the specified local port
try
{
socket = new MulticastSocket(port);
socket.joinGroup(multicastAddress); // Join the multicast group
}
catch (IOException e)
{
imageText = "Problem with multicast socket";
imageValid = false; changeImage(); return;
}
for (;;)
{
try
{
socket.receive(recvPacket); // Receive the image
}
catch (IOException e)
{ break; }
// Assume exception due to file closing
imageText = "";
imageValid = true;
changeImage();
recvPacket.setLength(MAXFILELEN);
// You have to reset this!!!
}
}
}