Java - Network

// Network

import java.net.InetAddress;

import java.net.UnknownHostException;

public class GetIP {

    public static void main(String[] args) throws UnknownHostException {

        

        // Get LocalHost IP

        InetAddress addr = InetAddress.getLocalHost();

        System.out.println(addr.getHostAddress());

        

        // Get Domain IP

        String domain = "www.sangmoo.xyz";

        addr = InetAddress.getByName(domain);

        System.out.println(addr.getHostAddress());

        

        // 특정 도메인에 여러 IP가 있을 경우

        domain = "www.youtube.com";

        InetAddress[] addrs = InetAddress.getAllByName(domain); // 여러 IP이기 때문에 []형식

        System.out.println(domain+" 에 연결된 IP들");

        for(InetAddress ip : addrs) {

            System.out.println(ip.getHostAddress());

        }

    }

}

// TCP는 연결 지향형이다. -> 소켓통신

// 신호가 끊기면 이어서 간다.

// 반면에 UDP는 중간에 끊기면 데이터를 버린다.

import java.io.IOException;

import java.net.InetSocketAddress;

import java.net.ServerSocket;

import java.net.Socket;

public class Server {

    public static void main(String[] args) throws IOException {

        

        ServerSocket server =null;

        try {

            // 1. 소켓생성

            server = new ServerSocket();

            // 2. IP 개방

            server.bind(new InetSocketAddress("localhost", 9000));

            // 3. 클라이언트 요청 대기

            while(true) {

                System.out.println("요청 대기 중");

                // 4. 요청에 따른 실행 및 응답

                Socket socket = server.accept();

                /*해야 할 일 수행 - Client의 주소 확인*/

                InetSocketAddress addr

                 = (InetSocketAddress) socket.getRemoteSocketAddress();

                System.out.println("Client 주소 확인 : "+addr.getAddress()+" : "+addr.getPort());

            }

        }

        catch (IOException e) {

            e.printStackTrace();

            // 5. 소켓 반납

            server.close();

            System.out.println("Server Close");

        }

    }

}

import java.io.IOException;

import java.net.InetSocketAddress;

import java.net.Socket;

public class Client {

    public static void main(String[] args) throws IOException {

        

        // 1. 소켓 생성

        Socket socket = new Socket();

        // 2. 접속 요청

        try {

            socket.connect(new InetSocketAddress("localhost", 9000));

            // 3. 요청이 받아지면 작업 수행

            System.out.println("접속 완료");

        } catch (IOException e) {

            e.printStackTrace();

        }

        // 4. 소켓 반납

        socket.close();

    }

}

* 에코 서버를 통해서 메세지를 보내고 받는 기능이 가능한지 판단 가능

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.OutputStreamWriter;

import java.net.InetSocketAddress;

import java.net.ServerSocket;

import java.net.Socket;

public class Server {

    public static void main(String[] args) throws IOException {

        

        ServerSocket server = null;

        

        try {

            // 1. 소켓 생성

            server = new ServerSocket();

            // 2. IP 개방

            server.bind(new InetSocketAddress("localhost",9000));

            // 3. 요청 대기

            while(true) {

                System.out.println("요청 대기 중");

                // 4. 접속 요청 수락

                Socket socket = server.accept();

                System.out.println("접속 수락");

                // 5. is와 os준비

                InputStream is = socket.getInputStream();

                OutputStream os = socket.getOutputStream();

                InputStreamReader reader = new InputStreamReader(is);

                OutputStreamWriter writer = new OutputStreamWriter(os, "utf-8");

                // 6. is와 os로 데이터 주고 받기

//              int data; // EOF가 없기 때문에 무한 루프가 된다.

//              while((data = reader.read()) != -1) {

//                  System.out.print(data);

//                  writer.write(data);

//              }

                

                // 방법 1 - 큰 배열 하나로 받아내는 방법

                char[] arr= new char[20];

                reader.read(arr); // while문이 없으므로 단 한번만 받아온다.

                String msg = new String(arr);

                System.out.println("받은 메세지 : "+msg);

                writer.write(msg);

                

//              // 방법 2 - EOF 대신 특정 문자로 대체 하는 방법

//              char data;

//              while(true) {

//                  data = (char) reader.read();

//                  System.out.print(data);

//                  writer.write(data);

//                  if(data == '~') {

//                      break;

//                  }

//              }

                

//              char[] b = new char[1024];

//              while(reader.read(b) != -1) {

//                  System.out.print("Client : "+b);

//                  writer.write(b);

//              }

                

                writer.flush();

                System.out.println("전송 완료");

                // 7. 자원 반납

                is.close();

                os.close();

                reader.close();

                writer.close();

            }

        } catch (IOException e) {

            e.printStackTrace();

            // 7. 자원 반납

            server.close();

        }

    }

}

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.OutputStreamWriter;

import java.net.InetSocketAddress;

import java.net.Socket;

public class Client {

    public static void main(String[] args) throws IOException {

        

        // 1. 소켓 생성

        Socket socket = new Socket();

        

        // 2. 접속 요청

        try {

            socket.connect(new InetSocketAddress("localhost", 9000));

            System.out.println("연결 완료");

            

            OutputStream os = socket.getOutputStream();

            OutputStreamWriter writer = new OutputStreamWriter(os, "utf-8");

            

            // 4. 데이터 전송

            String msg = "Hello, Server";

            writer.write(msg);

            writer.flush();

            System.out.println("전송 완료");

            

            // 5. 데이터 수신

            InputStream is = socket.getInputStream();

            InputStreamReader reader = new InputStreamReader(is);

            

            char[] arr = new char[20];

            reader.read(arr);

            String reply = new String(arr);

            System.out.println("받은 메세지 : " + msg);

            writer.write(reply);

            

            // 6. 자원 반납

            is.close();

            os.close();

            reader.close();

        } catch (IOException e) {

            e.printStackTrace();

        } finally {

            socket.close();

        }

    }

}