InetAddress cannot directly create an object, because its constructor permission modifier is the default, but it has a static method that can be called directly through the class name

InetAddress address = InetAddress.getByName("localhost");
System.out.println(address);//域名/IP地址
//getByName()中可以封装ip、域名等可以与ip映射的东西
System.out.println(address.getHostName());//获取域名
System.out.println(address.getHostAddress());//获取ip地址
 
//关于类InetSocketAddress
InetSocketAddress inetSocketAddress = new InetSocketAddress("192.168.199.217", 8080);
System.out.println(inetSocketAddress.getHostName());//获得域名
System.out.println(inetSocketAddress.getPort());//获得端口号
InetAddress address1 = inetSocketAddress.getAddress();//获得ip地址对象
System.out.println(address1.getHostName());//获得域名
System.out.println(address1.getHostAddress());//获得IP地址

communication related

TCP/IP architecture: the foundation of network communication.
Two important conditions for communication: IP+port (port)
Communication protocol: Certain rules must be followed when transmitting data between devices. This rule is called a communication protocol.

Socket

Role: the application layer obtains the transport layer protocol (TCP/UDP)

TCP protocol

Name: Transmission Control Protocol

Features:

reliable, connection-oriented
Three handshakes are established to establish a connection, and four handshakes are released to release the connection

Notice:

Need to open the server first to wait for client requests
Two-way communication between the client and the server, close the connection when the client inputs I want to close the connection

TCP practice operation

client

public class Customer {
    public static void main(String[] args) throws IOException {
        //创建套接字，指定服务器的IP和端口
        Socket socket = new Socket("127.0.0.1", 6666);
        socket.setSoTimeout(1000000);//设置连接超时时间，以ms为单位
        OutputStream outputStream = socket.getOutputStream();//获取输出流用来发送数据
        DataOutputStream dataOutputStream = new DataOutputStream(outputStream);//变成可处理字符串的输出流——装饰模式
        InputStream inputStream = socket.getInputStream();//获取输入流用来读数据
        DataInputStream dataInputStream = new DataInputStream(inputStream);//变成可处理字符串的输入流——装饰模式
        String s1="";
        while(!s1.equals("关闭")) {
            String s = new Scanner(System.in).nextLine();
            dataOutputStream.writeUTF(s);//给服务器发送数据——不阻塞
            s1 = dataInputStream.readUTF();//读取服务端信息——其为阻塞方法
            System.out.println(s1);
        }
        //以下为关流
        dataOutputStream.close();
        outputStream.close();
        socket.close();
    }
}

Server

public class Service {
    public static void main(String[] args) throws IOException {
        //创建套接字，监听6666端口
        ServerSocket serverSocket = new ServerSocket(6666);
        //accept()为阻塞方法，等待用户端数据，什么时候收到数据什么时候执行，返回值为客户端socket，接到这个socket后，客户端和服务器才真正建立连接，才真正可以通信了
        Socket accept = serverSocket.accept();
        InputStream inputStream = accept.getInputStream();//获取输入流，用来得到客户端数据
        DataInputStream dataInputStream = new DataInputStream(inputStream);//利用字符串处理流来读取字符串
        OutputStream outputStream = accept.getOutputStream();//获取输出流，用来向客户端写数据
        DataOutputStream dataOutputStream = new DataOutputStream(outputStream);
        String s1="";
        while(!s1.equals("关闭")) {
            String s = dataInputStream.readUTF();//读取客户端数据——其为阻塞方法
            System.out.println(s);//信息
            if(s.equals("我想关闭连接")){
                s1="关闭";
                dataOutputStream.writeUTF(s1);
            }else {
                s1 = new Scanner(System.in).nextLine();
                dataOutputStream.writeUTF(s1);//不阻塞
            }
        }
        //以下为关流
        dataInputStream.close();
        inputStream.close();
        accept.close();//客户端socket
        serverSocket.close();
    }
}//全写好之后运行该服务等待客户端请求

UDP protocol

Name: User Datagram Protocol

Features:

connectionless oriented
Split the data packets and send them to the destination one by one, and finally make a summary on the server side (there will be packet loss problems)

Notice:

Sender and receiver are equal
Two-way communication between the sender and the receiver, stop when the sender enters the next chat

UDP practice operation

sender

public class Send {
    public static void main(String[] args) throws IOException {
        //准备套接字，指定发送方的端口号
        DatagramSocket datagramSocket = new DatagramSocket(8888);
        String s1="";
        while(!s1.equals("bye bye")) {
            //发送阶段
            //准备数据包
            String s = new Scanner(System.in).nextLine();
            byte[] bytes = s.getBytes();
            //里面传接收方的IP地址对象及端口
            DatagramPacket localhost = new DatagramPacket(bytes, bytes.length, InetAddress.getByName("localhost"), 6666);
            //向目标地址发送数据包
            datagramSocket.send(localhost);//不是阻塞方法
 
            //接收阶段
            byte[] b = new byte[1024];
            DatagramPacket datagramPacket = new DatagramPacket(b, b.length);
            datagramSocket.receive(datagramPacket);
            byte[] data = datagramPacket.getData();
            s1 = new String(data, 0, datagramPacket.getLength());
            System.out.println(s1);
        }
        //关流
        datagramSocket.close();
    }
}

receiver

public class Get {
    public static void main(String[] args) throws IOException {
        DatagramSocket datagramSocket = new DatagramSocket(6666);//指定接收方的端口号
        boolean flag=true;
        while(flag) {
            //接收阶段
            //搞一个空数据包用来接收对方传过来的数据
            byte[] bytes = new byte[1024];
            DatagramPacket datagramPacket = new DatagramPacket(bytes, bytes.length);
            //接收对方发过来的数据包放入datagramPacket数据包中进行填充
            datagramSocket.receive(datagramPacket);//其为阻塞方法，接收数据包后，datagramPacket里面的内容就填充好了
            //取出数据
            byte[] data = datagramPacket.getData();
            String s = new String(data, 0, datagramPacket.getLength());//取出特定长度的字节数据转化为字符串类型
            System.out.println(s);
            if(s.equals("下次再聊")){
                DatagramPacket end = new DatagramPacket("bye bye".getBytes(), "bye bye".getBytes().length, InetAddress.getByName("localhost"), 8888);
                datagramSocket.send(end);
                flag=false;
            }else {
                //发送阶段
                //准备数据包
                String s1 = new Scanner(System.in).nextLine();
                byte[] b = s1.getBytes();
                DatagramPacket localhost = new DatagramPacket(b, b.length, InetAddress.getByName("localhost"), 8888);
                //向目标地址发送数据包
                datagramSocket.send(localhost);//不是阻塞方法
            }
        }
        //关流
        datagramSocket.close();
    }
}

Java HTTP request

Open the tomcat service to receive requests

@RestController
@RequestMapping("/hello")
public class MyController {
    @GetMapping("/getName")
    public String responseName(String name){
        return "你的名字为"+name;
    }
    @PostMapping("/getUser")
    public String responseUser(@RequestBody Map<String,Object> map){
        System.out.println(map);
        return "你的post请求发送成功";
    }
}

Note: The port I used here is 8088

HTTP sends GET request

public class HttpTest {
    public static void main(String[] args) throws Exception{
        //定义一个url字符串
        String urlstr = "http://localhost:8088/hello/getName?name=lili";
        //将url字符串转换为url对象
        URL url = new URL(urlstr);
        //通过该url对象创建连接
        URLConnection urlConnection = url.openConnection();
        //URLConnection为一个抽象类，我们需要HttpURLConnection
        HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
        //使用url.openConnection()创建了连接，connect()方法可有可无;
        //如果使用HttpURLConnection conn=new HttpURLConnection(new URL(“路径”))，则需要使用connect()方法进行连接。
        //httpURLConnection.connect();
        //设置请求头
        httpURLConnection.setRequestProperty("Accept-Charset", "utf-8");
        //设置请求类型
        httpURLConnection.setRequestMethod("GET");
        //设置连接超时时间10s
        httpURLConnection.setConnectTimeout(10000);
        //设置读取超时时间10秒
        httpURLConnection.setReadTimeout(10000);
        //允许从远程服务器中读取数据，默认为true
        httpURLConnection.setDoInput(true);
        //获取HttpURLConnection的输入流，用来读数据
        InputStream inputStream = httpURLConnection.getInputStream();
        //装饰模式，处理流对该流进行处理
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream, "UTF-8");
        //该处理流用来增加处理效率
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        String line;
        StringBuilder all = new StringBuilder();
        //若该行数据不为空，则追加到all
        while ((line = bufferedReader.readLine()) != null) {
            all.append(line);
        }
        System.out.println(all);
        //获得响应状态码
        int responseCode = httpURLConnection.getResponseCode();
        System.out.println(responseCode);
        //关流
        bufferedReader.close();
        inputStreamReader.close();
        inputStream.close();
        //关闭连接
        httpURLConnection.disconnect();
    }
}

HTTP send POST request

public class HttpTestPost {
    public static void main(String[] args) throws Exception{
        //定义一个url字符串
        String urlstr = "http://localhost:8088/hello/getUser";
        //将url字符串转换为url对象
        URL url = new URL(urlstr);
        //通过该url对象创建连接
        URLConnection urlConnection = url.openConnection();
        //URLConnection为一个抽象类，我们需要HttpURLConnection
        HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
        //设置请求头
        httpURLConnection.setRequestProperty("appId", "app_service");
        //设置请求类型
        httpURLConnection.setRequestMethod("POST");
        //设置请求体格式，这里设置的是json格式
        httpURLConnection.setRequestProperty("Content-Type", "application/json; charset=utf-8;");
        //设置连接超时时间10s
        httpURLConnection.setConnectTimeout(10000);
        //设置请求体
        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("name","lili");
        map.put("age",18);
        //将usermap转化为json格式
        ObjectMapper mapper = new ObjectMapper();
        String jsonBody = mapper.writeValueAsString(map);
        //设置成true，向远程服务器写数据,默认是false
        httpURLConnection.setDoOutput(true);
        OutputStream outputStream = httpURLConnection.getOutputStream();
        outputStream.write(jsonBody.getBytes());
        outputStream.flush();
        //关流
        outputStream.close();
        //允许从远程服务器中读取数据，默认为true
        //httpURLConnection.setDoInput(true);
        //获取HttpURLConnection的输入流，用来读数据
        InputStream inputStream = httpURLConnection.getInputStream();
        //装饰模式，处理流对该流进行处理
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream, "UTF-8");
        //该处理流用来增加处理效率
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        String line;
        StringBuilder all = new StringBuilder();
        //若该行数据不为空，则追加到all
        while ((line = bufferedReader.readLine()) != null) {
            all.append(line);
        }
        System.out.println(all);
        //获得响应状态码
        int responseCode = httpURLConnection.getResponseCode();
        System.out.println(responseCode);
        //关流
        bufferedReader.close();
        inputStreamReader.close();
        inputStream.close();
        //关闭连接
        httpURLConnection.disconnect();
    }
}

Notice:

There is no need to create a connection after using url.openConnection() to create a connection
Using HttpURLConnection conn=new HttpURLConnection(new URL("path")), you need to use the connect() method to connect.
The httpURLConnection.setDoInput(true) method is to allow reading data from the remote server, the default is true
The httpURLConnection.setDoOutput(true) method is to allow writing data to the remote server, the default is false

Network programming and HTTP requests

IP and port operation

communication related

Socket

TCP protocol

Features:

TCP practice operation

client

Server

UDP protocol

Features:

UDP practice operation

sender

receiver

Java HTTP request

Open the tomcat service to receive requests

HTTP sends GET request

HTTP send POST request

Notice:

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