Java网络编程之UDP实现原理解析

public class UdpClient {

	public static void main(String[] args) {
		try {
			Scanner scanner = new Scanner(System.in);
			User user = new User();
			System.out.print("请输入用户名》》");
			String userName = scanner.next();
			if (Operation.userIsExist(userName)) {
				//如果此用户已经注册过，直接把注册时用的接收端口分配给他
				user = Operation.findUserByName(userName);
			}else {
				//未注册，用户自己指定端口
				while(true) {
					System.out.println("请输入接收端口》》");
					int port = Integer.parseInt(scanner.next());
					if (Operation.portIsExist(port)) {
						System.err.println("该端口已被使用，请重新输入。。。。");
						continue;
					}else {
						user.setName(userName);
						user.setPort(port);
						Operation.addUser(user);
						break;
					}
				}
			}
			new Thread(new SendMsg(user)).start();
			new Thread(new ReceiveMsg(user)).start();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

public class SendMsg implements Runnable{

	private User self = null;
	private DatagramSocket socket = null;
	private BufferedReader reader = null;
	public SendMsg(User self) {
		try {
			socket = new DatagramSocket();
			reader = new BufferedReader(new InputStreamReader(System.in));
			this.self = self;
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	@Override
	public void run() {	
		try {
			while(true) {
				String[] msg = reader.readLine().split("@");
				if (msg.length != 2) {
					System.err.println("注意格式：消息@对方名字（私聊）或all（群聊）");
					continue;
				}
				msg[0] = self.getName()+"说："+msg[0];
				byte[] data = msg[0].getBytes();
				String toPerson = msg[1];
				if (("all").equals(toPerson)) {
					//群聊，获取所有用户，不管对方在不在线，都发过去
					List<User> users = Operation.getUsers();
					for(User user:users) {
						if (self != user) {
							DatagramPacket packet = new DatagramPacket(data, 0,data.length,new InetSocketAddress("localhost",user.getPort()));
						    socket.send(packet);
						}
					}
				}else {
					//私聊
					try {
						DatagramPacket packet = new DatagramPacket(data, 0,data.length,new InetSocketAddress("localhost",Operation.findUserByName(toPerson).getPort()));
				        socket.send(packet);
					} catch (Exception e) {
						System.out.println("对方不在线。。。");
					}
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

public class ReceiveMsg implements Runnable{

	private DatagramSocket socket = null;
	public ReceiveMsg(User user) {
		try {
			socket = new DatagramSocket(user.getPort());
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	@Override
	public void run() {
		try {
			while(true) {
				//准备接收包裹
				byte[] container = new byte[1024];
				DatagramPacket packet = new DatagramPacket(container,0,container.length);
				socket.receive(packet);
				byte[]data = packet.getData();
				String receiveData = new String(data, 0, data.length);
				System.out.println(receiveData);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		socket.close();
	}
}

public class Operation {
	private static String FILE_PATH = "config/user.xml";     //文件目录
 
        //在xml文件中添加一个用户信息
	public static void addUser(User user)
	{
		InputStream in = null;
		SAXReader reader = new SAXReader();
		Document doc = null;
		try
		{
			in = new FileInputStream(FILE_PATH);
			doc = reader.read(in);
			Element root = doc.getRootElement();   //获取xml根节点，即users节点
			Element element = root.addElement("user");
			element.addElement("name").addText(user.getName());
			element.addElement("port").addText(String.valueOf(user.getPort()));
 
			FileOutputStream fos = new FileOutputStream(FILE_PATH);
			//格式化xml文件
			OutputFORMat format = OutputFormat.createPrettyPrint();
			format.setEncoding("utf-8");
			XMLWriter writer = new XMLWriter(fos,format);
			writer.write(doc);
			writer.close();
		}
		catch (Exception e)
		{
			System.out.println("error");
		}
		finally
		{
			try
			{
			
				if(in != null)
					in.close();
			}
			catch (IOException e)
			{
				System.out.println("error");
			}
		}
	}
 
        //列出xml中所有用户信息
	public static List<User> getUsers()
	{
		InputStream in = null;
		SAXReader reader = new SAXReader();
		Document doc = null;
		List<User> users = new ArrayList<>();
		try
		{
			in = new FileInputStream(FILE_PATH);
			doc = reader.read(in);
			Element root = doc.getRootElement();
			List<Element> elements = root.elements();
			for (Element element : elements)
			{
				User user = new User();
				user.setName(element.elementText("name"));
				user.setPort(Integer.valueOf(element.elementText("port")));
				users.add(user);
			}
		}
		catch (Exception e1)
		{
			System.out.println("error");
		}
		finally
		{
			try
			{
				in.close();
			}
			catch (IOException e)
			{
				System.out.println("error");
			}
		}
 
		return users;
	}
	public static User findUserByName(String name) {
		InputStream in = null;
		SAXReader reader = new SAXReader();
		Document doc = null;
		try {
			in = new FileInputStream(FILE_PATH);
			doc = reader.read(in);
			Element root = doc.getRootElement();
			List<Element> elements = root.elements();
			for (Element element : elements)
			{
				if(name != null && name.equals(element.elementText("name"))) {
					User user = new User();
					user.setName(name);
					user.setPort(Integer.parseInt(element.elementText("port")));
					return user;
				}
			}
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (DocumentException e) {
			e.printStackTrace();
		}
		return null;
	}
	
	public static boolean portIsExist(int port) {
		InputStream in = null;
		SAXReader reader = new SAXReader();
		Document doc = null;
		
		try {
			in = new FileInputStream(FILE_PATH);
			doc = reader.read(in);
			Element root = doc.getRootElement();
			List<Element> elements = root.elements();
			for (Element element : elements)
			{
				if(port == Integer.parseInt(element.elementText("port")))
					return true;
			}
			
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (DocumentException e) {
			e.printStackTrace();
		}
		return false;
	}
        //判断某个用户是否存在该xml中
	public static boolean userIsExist(String name) 
	{
		InputStream in = null;
		SAXReader reader = new SAXReader();
		Document doc = null;
		try {
			in = new FileInputStream(FILE_PATH);
			doc = reader.read(in);
			Element root = doc.getRootElement();
			List<Element> elements = root.elements();
			for (Element element : elements)
			{
				if(name != null && name.equals(element.elementText("name")))
					return true;
			}
			
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (DocumentException e) {
			e.printStackTrace();
		}
		return false;
	}
}

public class User implements Serializable{

	private String name;//姓名
	private int port;//接收端口
	public String getName() {
		return name;
	}
	public int getPort() {
		return port;
	}
	public void setName(String name) {
		this.name = name;
	}
	public void setPort(int port) {
		this.port = port;
	}
	@Override
	public String toString() {
		return "User [name=" + name + ", port=" + port + "]";
	}
	
}