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Java网络编程之UDP实现原理解析

时间:2021-12-20 13:35     来源/作者:计院阮小杰

UDP实现通信非常简单,没有服务器,每个都是客户端,每个客户端都需要一个发送端口和一个接收端口。一个客户端向另一个客户端发送消息时,需要知道对方的IP和接收端口,所用到的类为DatagramSocket。

DatagramSocket socket =new DatagramSocket(),发送端socket,若不指定端口,系统自动分配

DatagramSocket socket =new DatagramSocket("接收信息端口"),接收端socket,需要指定接收端口

​ 若想客户端之间进行全双工通信,每个客户端都要有两个线程,一个用于发送信息,一个用于接收信息。

​ 那么UDP怎么实现私聊和群聊呢?(在本机一台电脑的情况下实现)

​ 首先私聊,客户端向另一个客户端发送消息,就要知道其IP(本机都是固定的localhost)和接收端口,也需要姓名进行标识,所以,每个客户端都至少要自己的姓名和接收端口,而且端口不可重复,否则会报端口被占用的错。

​ 其次群聊,由于在本机一台电脑上进行,接收端口各不相同,所以广播就不行了,此时就希望每个客户端在启动的时候,能够把自己的姓名和接收端口给存起来,然后就可以遍历进行群聊。

​ 实现:

  • 第一种,在每个客户端启动时,输入自己的姓名和接收端口,发送信息时,需要输入对方的接收端口号,如果输入时输入了多个端口,就是群发。那么这样每次发送信息时都要指定对方的端口。。。
  • 第二种,客户端启动时,输入姓名和接收端口,此时就把数据存起来,发送信息时,只用指定对方姓名即可。。。可用数据库存,可用文件存,我用的是XML来存。

要创建xml文件,路径在Operation类中

UdpClient.java:

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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();
        }
    }
}

发送信息:

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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();
        }
    }
}

接收消息:

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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();
    }
}

操作XML文件类:

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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;
    }
}

用户实体类:

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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 + "]";
    }
    
}

运行结果:
Java网络编程之UDP实现原理解析

Java网络编程之UDP实现原理解析

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原文链接:https://www.cnblogs.com/it-ruanjie/p/15225456.html

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