1、UDP
- 用户数据报协议，又称用户数据报文协议
- 简单的面向数据报的传输层协议
- 用户数据协议，非连接协议
- 不可靠、结构简单、无校验、速度快、容易丢包、可广播
2.应用
- DNS、TFTP、SNMP
- 视频、音频（直播）；普通数据（无关紧要数据）
3.UDP包最大长度
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4.UDP局域网搜索
4.1UDP 提供者，用于提供服务
public class UDPProvider {
public static void main(String[] args) throws IOException {
// 生成一份唯一标示
String sn = UUID.randomUUID().toString();
Provider provider = new Provider(sn);
provider.start();
// 读取任意键盘信息后可以退出
//noinspection ResultOfMethodCallIgnored
System.in.read();
provider.exit();
}
private static class Provider extends Thread {
private final String sn;
private boolean done = false;
private DatagramSocket ds = null;
public Provider(String sn) {
super();
this.sn = sn;
}
@Override
public void run() {
super.run();
System.out.println("UDPProvider Started.");
try {
// 监听20000 端口
ds = new DatagramSocket(20000);
while (!done) {
// 构建接收实体
final byte[] buf = new byte[512];
DatagramPacket receivePack = new DatagramPacket(buf, buf.length);
// 接收
ds.receive(receivePack);
// 打印接收到的信息与发送者的信息
// 发送者的IP地址
String ip = receivePack.getAddress().getHostAddress();
int port = receivePack.getPort();
int dataLen = receivePack.getLength();
String data = new String(receivePack.getData(), 0, dataLen);
System.out.println("UDPProvider receive form ip:" + ip
+ "\tport:" + port + "\tdata:" + data);
// 解析端口号
int responsePort = MessageCreator.parsePort(data);
if (responsePort != -1) {
// 构建一份回送数据
String responseData = MessageCreator.buildWithSn(sn);
byte[] responseDataBytes = responseData.getBytes();
// 直接根据发送者构建一份回送信息
DatagramPacket responsePacket = new DatagramPacket(responseDataBytes,
responseDataBytes.length,
receivePack.getAddress(),
responsePort);
ds.send(responsePacket);
}
}
} catch (Exception ignored) {
} finally {
close();
}
// 完成
System.out.println("UDPProvider Finished.");
}
private void close() {
if (ds != null) {
ds.close();
ds = null;
}
}
/**
* 提供结束
*/
void exit() {
done = true;
close();
}
}
}
4.2UDP 搜索者，用于搜索服务支持方
public class UDPSearcher {
private static final int LISTEN_PORT = 30000;
public static void main(String[] args) throws IOException, InterruptedException {
System.out.println("UDPSearcher Started.");
Listener listener = listen();
sendBroadcast();
// 读取任意键盘信息后可以退出
//noinspection ResultOfMethodCallIgnored
System.in.read();
List devices = listener.getDevicesAndClose();
for (Device device : devices) {
System.out.println("Device:" + device.toString());
}
// 完成
System.out.println("UDPSearcher Finished.");
}
private static Listener listen() throws InterruptedException {
System.out.println("UDPSearcher start listen.");
CountDownLatch countDownLatch = new CountDownLatch(1);
Listener listener = new Listener(LISTEN_PORT, countDownLatch);
listener.start();
countDownLatch.await();
return listener;
}
private static void sendBroadcast() throws IOException {
System.out.println("UDPSearcher sendBroadcast started.");
// 作为搜索方，让系统自动分配端口
DatagramSocket ds = new DatagramSocket();
// 构建一份请求数据
String requestData = MessageCreator.buildWithPort(LISTEN_PORT);
byte[] requestDataBytes = requestData.getBytes();
// 直接构建packet
DatagramPacket requestPacket = new DatagramPacket(requestDataBytes,
requestDataBytes.length);
// 20000端口, 广播地址
requestPacket.setAddress(InetAddress.getByName("255.255.255.255"));
requestPacket.setPort(20000);
// 发送
ds.send(requestPacket);
ds.close();
// 完成
System.out.println("UDPSearcher sendBroadcast finished.");
}
private static class Device {
final int port;
final String ip;
final String sn;
private Device(int port, String ip, String sn) {
this.port = port;
this.ip = ip;
this.sn = sn;
}
@Override
public String toString() {
return "Device{" +
"port=" + port +
", ip='" + ip + '\'' +
", sn='" + sn + '\'' +
'}';
}
}
private static class Listener extends Thread {
private final int listenPort;
/**
* 同步辅助类
*/
private final CountDownLatch countDownLatch;
private final List devices = new ArrayList<>();
private boolean done = false;
private DatagramSocket ds = null;
public Listener(int listenPort, CountDownLatch countDownLatch) {
super();
this.listenPort = listenPort;
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
super.run();
// 通知已启动
countDownLatch.countDown();
try {
// 监听回送端口
ds = new DatagramSocket(listenPort);
while (!done) {
// 构建接收实体
final byte[] buf = new byte[512];
DatagramPacket receivePack = new DatagramPacket(buf, buf.length);
// 接收
ds.receive(receivePack);
// 打印接收到的信息与发送者的信息
// 发送者的IP地址
String ip = receivePack.getAddress().getHostAddress();
int port = receivePack.getPort();
int dataLen = receivePack.getLength();
String data = new String(receivePack.getData(), 0, dataLen);
System.out.println("UDPSearcher receive form ip:" + ip
+ "\tport:" + port + "\tdata:" + data);
String sn = MessageCreator.parseSn(data);
if (sn != null) {
Device device = new Device(port, ip, sn);
devices.add(device);
}
}
} catch (Exception ignored) {
} finally {
close();
}
System.out.println("UDPSearcher listener finished.");
}
private void close() {
if (ds != null) {
ds.close();
ds = null;
}
}
List getDevicesAndClose() {
done = true;
close();
return devices;
}
}
}
public class MessageCreator {
private static final String SN_HEADER = "收到暗号，我是（SN）:";
private static final String PORT_HEADER = "这是暗号，请回电端口（Port）:";
public static String buildWithPort(int port) {
return PORT_HEADER + port;
}
public static int parsePort(String data) {
if (data.startsWith(PORT_HEADER)) {
return Integer.parseInt(data.substring(PORT_HEADER.length()));
}
return -1;
}
public static String buildWithSn(String sn) {
return SN_HEADER + sn;
}
public static String parseSn(String data) {
if (data.startsWith(SN_HEADER)) {
return data.substring(SN_HEADER.length());
}
return null;
}
}