发送和接收UDP数据包？
发送和接收UDP数据包？
提问于 2012-05-12 02:37:35
我编写了一个程序，将UDP数据包从客户端发送到服务器。
以下是发送器代码：
import java.io.IOException;
import java.net.*;
public class JavaApplication9 {
public static void main(String[] args) throws UnknownHostException, SocketException, IOException {
// TODO code application logic here
byte[] buffer = {10,23,12,31,43,32,24};
byte [] IP = {-64,-88,1,106};
InetAddress address = InetAddress.getByAddress(IP);
DatagramPacket packet = new DatagramPacket(
buffer, buffer.length, address, 57
);
DatagramSocket datagramSocket = new DatagramSocket();
datagramSocket.send(packet);
System.out.println(InetAddress.getLocalHost().getHostAddress());
}
}接收器代码函数如下：
public void run() {
try {
DatagramSocket serverSocket = new DatagramSocket(port);
byte[] receiveData = new byte[8];
byte[] sendData = new byte[8];
while (true) {
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
String sentence = new String( receivePacket.getData());
System.out.println("RECEIVED: " + sentence);
InetAddress IPAddress = receivePacket.getAddress();
String sendString = "polo";
sendData = sendString.getBytes();
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);
serverSocket.send(sendPacket);
}
} catch (IOException e) {
e.printStackTrace();
}
}我使用过Wireshark程序。UDP数据包在接收器的Wireshark程序中被接收，但是Java程序不会识别它，程序只是继续侦听端口而没有任何反应？
回答 1
Stack Overflow用户
发布于 2012-12-09 02:41:13
接收方必须将接收方端口设置为与发送方DatagramPacket中设置的端口相匹配。对于调试，请尝试侦听大于1024的端口(例如5000或9000)。端口< 1024通常由系统服务使用，需要管理员权限才能在此类端口上绑定。
如果接收方将数据包发送到它正在侦听的硬编码端口(例如端口57)，而发送方在同一台机器上，那么您将创建一个环回到接收方本身。请始终使用数据包中指定的端口，如果是生产软件，则需要进行检查以防止出现这种情况。
数据包无法到达目的地的另一个原因是发送方指定的IP地址错误。与TCP不同的是，UDP将尝试发送数据包，即使地址不可达，发送方也不会收到错误指示。作为调试的预防措施，您可以通过在接收器中打印地址来进行检查。
在您设置的发件人中：
byte [] IP= { (byte)192, (byte)168, 1, 106 };
InetAddress address = InetAddress.getByAddress(IP);但使用字符串形式的地址可能会更简单：
InetAddress address = InetAddress.getByName("192.168.1.106");换句话说，您将目标设置为192.168.1.106。如果这不是接收器，那么您将不会收到数据包。
下面是一个简单的UDP接收器：
import java.io.IOException;
import java.net.*;
public class Receiver {
public static void main(String[] args) {
int port = args.length == 0 ? 57 : Integer.parseInt(args[0]);
new Receiver().run(port);
}
public void run(int port) {
try {
DatagramSocket serverSocket = new DatagramSocket(port);
byte[] receiveData = new byte[8];
String sendString = "polo";
byte[] sendData = sendString.getBytes("UTF-8");
System.out.printf("Listening on udp:%s:%d%n",
InetAddress.getLocalHost().getHostAddress(), port);
DatagramPacket receivePacket = new DatagramPacket(receiveData,
receiveData.length);
while(true)
{
serverSocket.receive(receivePacket);
String sentence = new String( receivePacket.getData(), 0,
receivePacket.getLength() );
System.out.println("RECEIVED: " + sentence);
// now send acknowledgement packet back to sender
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length,
receivePacket.getAddress(), receivePacket.getPort());
serverSocket.send(sendPacket);
}
} catch (IOException e) {
System.out.println(e);
}
// should close serverSocket in finally block
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/10556829
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