1. InetAddress

InetAddress的常用方法如下：

public class InetAddressDemo {
    public static void main(String[] args) throws Exception{
        // 1. 获取本机IP地址对象
        InetAddress ip1 = InetAddress.getLocalHost();
        System.out.println(ip1.getHostName());
        System.out.println(ip1.getHostAddress());

        // 2. 获取指定IP或者域名的IP地址对象
        InetAddress ip2 = InetAddress.getByName("www.baidu.com");
        System.out.println(ip2.getHostName());
        System.out.println(ip2.getHostAddress());

        // 3. 与对方地址是否可以联通
        System.out.println(ip2.isReachable(6));
    }
}

2. UDP

客户端

package Socket.UDP;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.Scanner;

public class Client {
    public static void main(String[] args) throws Exception{
        // 1. 创建客户端对象
        DatagramSocket socket = new DatagramSocket();

        Scanner sc = new Scanner(System.in);
        while (true) {
            System.out.println("请输入发送的数据,输入exit退出：");
            String message = sc.nextLine();
            if(message.equals("exit"))
                break;
            byte[] data = message.getBytes();
            // 2. 创建数据包对象封装要发出去的数据
            /**
             * 参数一：封装要发出去的数据
             * 参数二：长度
             * 参数三：服务端IP地址
             * 参数四：端口号
             */
            DatagramPacket packet = new DatagramPacket(data, data.length,
                    InetAddress.getLocalHost(), 6666);
            // 3. 开始发送数据
            socket.send(packet);
        }
        // 4. 释放资源
//        System.out.println("客户端数据发送完毕！");
        socket.close();
    }
}

服务端

package Socket.UDP;

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class Server {
    public static void main(String[] args) throws Exception{
        // 1. 创建一个服务端对象
        DatagramSocket socket = new DatagramSocket(6666);
        // 2. 创建一个数据包对象，用于接收数据对象
        while (true) {
            byte[] buf = new byte[1024];    // 1KB
            DatagramPacket packet = new DatagramPacket(buf, buf.length);
            // 3. 开始正式使用数据包来接收客户端发来的数据
            socket.receive(packet);
            // 4. 打印数据
            String res = new String(buf, 0, packet.getLength());
            System.out.println(res);
        }
    }
}

3. TCP

客户端

服务端

实现一个多人聊天室
这个小demo当时大二的时候自己写，用C++写了400多行代码，没想到java总共就100多行，哈哈哈~一是感叹java封装的好，而是觉得，当时觉得特别难特别自豪的一个项目，现在看来只是入门的一个小demo，不过心里更多是感慨这一两年内的成长变化太大了吧。

ServerReadThread

package Socket.TCP;

import java.io.*;
import java.net.Socket;

public class ServerReadThread extends Thread{
    private Socket socket;
    private String name;
    public ServerReadThread(Socket t) {
        socket = t;
        name = Thread.currentThread().getName();
    }
    @Override
    public void run() {
        try {
            InputStream is = socket.getInputStream();
            DataInputStream dis = new DataInputStream(is);
            while(true) {
                try {
                    String msg = dis.readUTF();
                    System.out.println(name + ": " + msg);
                    sendMessage2All(msg);
                } catch (IOException e) {
                    System.out.println(socket.getLocalAddress() + "下线了");
                    Server.onLineSockets.remove(socket);
                    dis.close();
                    socket.close();
                    break;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private void sendMessage2All(String msg) throws Exception {
        for (Socket onLineSocket : Server.onLineSockets) {
            OutputStream os = onLineSocket.getOutputStream();
            DataOutputStream dos = new DataOutputStream(os);
            dos.writeUTF(msg);
            dos.flush();
        }
    }
}

服务端代码

package Socket.TCP;

import java.io.DataInputStream;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class Server {
    public static List<Socket> onLineSockets = new ArrayList<>();
    public static void main(String[] args) throws Exception{
        // 1. 创建对象
        ServerSocket ss = new ServerSocket(8888);
        System.out.println("服务端启动成功");
        while(true) {
            Socket socket = ss.accept();
            onLineSockets.add(socket);
            new ServerReadThread(socket).start();
            System.out.println("Hello, " + socket.getLocalAddress());
        }
    }
}

ClientReader

package Socket.TCP;

import java.io.*;
import java.net.Socket;

public class ClientReader extends Thread{
    private Socket socket;
    private String name;
    public ClientReader(Socket s) {
        socket = s;
        name = Thread.currentThread().getName();
    }
    @Override
    public void run() {
        try {
            InputStream is = socket.getInputStream();
            DataInputStream dis = new DataInputStream(is);
            while(true) {
                try {
                    String msg = dis.readUTF();
                    System.out.println(name + ": " + msg);
                    sendMessage2All(msg);
                } catch (IOException e) {
                    System.out.println(socket.getLocalAddress() + "下线了");
                    dis.close();
                    socket.close();
                    break;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private void sendMessage2All(String msg) throws Exception {
        for (Socket onLineSocket : Server.onLineSockets) {
            OutputStream os = onLineSocket.getOutputStream();
            DataOutputStream dos = new DataOutputStream(os);
            dos.writeUTF(msg);
            dos.flush();
        }
    }
}

客户端代码

package Socket.TCP;

import java.io.DataOutputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.util.Scanner;

public class Client {
    public static void main(String[] args) throws Exception{
        // 1. 创建Socket对象，并同时请求与服务端程序的连接
        Socket socket = new Socket("127.0.0.1", 8888);
        OutputStream os = socket.getOutputStream();
        DataOutputStream dos = new DataOutputStream(os);
        Scanner sc = new Scanner(System.in);

        // 创建线程负责收消息
        new ClientReader(socket).start();

        while(true) {
            System.out.println("请发送消息：");
            String msg = sc.nextLine();
            if("exit".equals(msg)) {
                System.out.println("bye~");
                break;
            }
            dos.writeUTF(msg);
            dos.flush();
        }
        dos.close();
        socket.close();
    }
}

4. 总结

到这，Java基本的一些东西就学的差不多了，后面还剩一些Java高级，比如反射注解这些，再学一下吧。目前只能说快速拉通了一遍API，但是熟悉程度肯定没有我用了3年的C++熟悉的，后面还是要多用才行，有机会做个小项目吧。还有就是各种数据结构，这点通过去刷力扣应该就能更熟悉了。目前对我来说，没什么压力学习起来，等过几天我会再好好整理一下我的未来的一个规划的。今天就先到这告一段落了~