先存个档

2 years ago · 3fc7f6131a
commit 3fc7f6131a
26 changed files with 1184 additions and 0 deletions
--- a/.gitignore
+++ b/.gitignore
@ -0,0 +1,33 @@
+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
--- a/exp1-oop/pom.xml
+++ b/exp1-oop/pom.xml
@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>net.lensfrex</groupId>
+        <artifactId>lesson</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>exp1-oop</artifactId>
+
+    <properties>
+        <maven.compiler.source>8</maven.compiler.source>
+        <maven.compiler.target>8</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>
--- a/exp1-oop/src/main/java/net/lensfrex/AbstractExtends.java
+++ b/exp1-oop/src/main/java/net/lensfrex/AbstractExtends.java
@ -0,0 +1,30 @@
+package net.lensfrex;
+
+public class AbstractExtends {
+    protected void run() {
+        Father father = new Child();
+
+        father.method1();
+        father.method2();
+    }
+}
+
+// ------------------------------------------
+abstract class Father {
+    public abstract void method1();
+
+    public abstract void method2();
+}
+
+// -------------------------------------------
+class Child extends Father {
+    @Override
+    public void method1() {
+        System.out.println("Do some thing in method1");
+    }
+
+    @Override
+    public void method2() {
+        System.out.println("Do some thing in method2");
+    }
+}
--- a/exp1-oop/src/main/java/net/lensfrex/Interface.java
+++ b/exp1-oop/src/main/java/net/lensfrex/Interface.java
@ -0,0 +1,26 @@
+package net.lensfrex;
+
+public class Interface {
+    protected void run() {
+        AnInterface anInterface = new AnInterface() {
+            @Override
+            public void method1() {
+                System.out.println("Do some thing in method1");
+            }
+
+            @Override
+            public void method2() {
+                System.out.println("Do some thing in method2");
+            }
+        };
+
+        anInterface.method1();
+        anInterface.method2();
+    }
+}
+
+interface AnInterface {
+    void method1();
+
+    void method2();
+}
--- a/exp1-oop/src/main/java/net/lensfrex/Main.java
+++ b/exp1-oop/src/main/java/net/lensfrex/Main.java
@ -0,0 +1,51 @@
+package net.lensfrex;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+
+public class Main {
+    public static void main(String[] args) throws Exception {
+        if (args.length > 0) {
+            execute(args[0]);
+        } else {
+            System.out.println("Witch to run? (1, 2, 3)");
+            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+
+            execute(reader.readLine());
+        }
+    }
+
+    private static void execute(String option) {
+        Main main = new Main();
+
+        switch (option) {
+            case "1":
+                main.run1();
+                break;
+            case "2":
+                main.run2();
+                break;
+            case "3":
+                main.run3();
+                break;
+            default:
+                System.out.printf("Invalid input for '%s'%n", option);
+        }
+    }
+
+    private void run1() {
+        Rectangle rectangle = new Rectangle(3, 4);
+
+        System.out.println("rectangleHeight: " + rectangle.getHeight());
+        System.out.println("rectangleWidth: " + rectangle.getWidth());
+        System.out.println("rectangleSize: " + rectangle.getSize());
+    }
+
+    private void run2() {
+        new Interface().run();
+    }
+
+    private void run3() {
+        new AbstractExtends().run();
+    }
+}
--- a/exp1-oop/src/main/java/net/lensfrex/Rectangle.java
+++ b/exp1-oop/src/main/java/net/lensfrex/Rectangle.java
@ -0,0 +1,33 @@
+package net.lensfrex;
+
+public class Rectangle {
+    private float height = 0;
+    private float width = 0;
+
+    public Rectangle() {}
+
+    public Rectangle(float height, float width) {
+        this.height = height;
+        this.width = width;
+    }
+
+    public float getSize() {
+        return height * width;
+    }
+
+    public float getHeight() {
+        return height;
+    }
+
+    public void setHeight(float height) {
+        this.height = height;
+    }
+
+    public float getWidth() {
+        return width;
+    }
+
+    public void setWidth(float width) {
+        this.width = width;
+    }
+}
--- a/exp2-thread/pom.xml
+++ b/exp2-thread/pom.xml
@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>net.lensfrex</groupId>
+        <artifactId>lesson</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>exp2-thread</artifactId>
+
+    <properties>
+        <maven.compiler.source>8</maven.compiler.source>
+        <maven.compiler.target>8</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>
--- a/exp2-thread/src/main/java/net/lensfrex/Main.java
+++ b/exp2-thread/src/main/java/net/lensfrex/Main.java
@ -0,0 +1,42 @@
+package net.lensfrex;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+
+public class Main {
+    public static void main(String[] args) throws Exception {
+        System.out.println("Thread Lesson report");
+
+        if (args.length > 0) {
+            execute(args[0]);
+        } else {
+            System.out.println("Witch to run? (1, 2)");
+            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+
+            execute(reader.readLine());
+        }
+    }
+
+    private static void execute(String option) {
+        Main main = new Main();
+
+        switch (option) {
+            case "1":
+                main.run1();
+                break;
+            case "2":
+                main.run2();
+                break;
+            default:
+                System.out.printf("Invalid input for '%s'%n", option);
+        }
+    }
+
+    private void run1() {
+        new RabbitAndTortoise().runTest();
+    }
+
+    private void run2() {
+        new Ticket().runTest();
+    }
+}
--- a/exp2-thread/src/main/java/net/lensfrex/RabbitAndTortoise.java
+++ b/exp2-thread/src/main/java/net/lensfrex/RabbitAndTortoise.java
@ -0,0 +1,42 @@
+package net.lensfrex;
+
+public class RabbitAndTortoise {
+    public void runTest() {
+        Animal rabbit = new Animal("Rabbit", 16, 32);
+        Animal tortoise = new Animal("Tortoise", 8, 32);
+
+        new Thread(rabbit).start();
+        new Thread(tortoise).start();
+    }
+}
+
+class Animal implements Runnable {
+    private final String name;
+
+    private final int speed;
+    private final int targetDistance;
+
+    private int totalDistance = 0;
+
+    public Animal(String name, int speed, int targetDistance) {
+        this.name = name;
+        this.speed = speed;
+        this.targetDistance = targetDistance;
+    }
+
+    @Override
+    public void run() {
+        while (totalDistance <= targetDistance) {
+            try {
+                Thread.sleep((int) (Math.random() * 1000) + 500);
+            } catch (Exception ignored) {
+                return;
+            }
+
+            totalDistance += speed;
+            System.out.printf("[%s] has run %d%n", name, totalDistance);
+        }
+
+        System.out.printf("[%s] has finish the game.%n", name);
+    }
+}
--- a/exp2-thread/src/main/java/net/lensfrex/Ticket.java
+++ b/exp2-thread/src/main/java/net/lensfrex/Ticket.java
@ -0,0 +1,40 @@
+package net.lensfrex;
+
+public class Ticket {
+    public void runTest() {
+        TicketOffice ticketOffice = new TicketOffice();
+        new Thread(ticketOffice, "0").start();
+        new Thread(ticketOffice, "1").start();
+        new Thread(ticketOffice, "2").start();
+    }
+}
+
+class TicketOffice implements Runnable {
+    private static int ticket = 8;
+
+    @Override
+    public void run() {
+        String name = Thread.currentThread().getName();
+        while(sellTicket(name));
+    }
+
+    private boolean sellTicket(String name) {
+        synchronized (this) {
+            if (ticket <= 0) {
+                System.out.printf("[%s]: Ticket was sold out.%n", name);
+                return false;
+            }
+
+            System.out.printf("TicketOffice '%s' is selling ticket No.%s%n", name, ticket);
+            ticket--;
+
+            try {
+                Thread.sleep(128);
+            } catch (Exception ignored) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}
--- a/exp3-network/pom.xml
+++ b/exp3-network/pom.xml
@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>net.lensfrex</groupId>
+        <artifactId>lesson</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>exp3-network</artifactId>
+
+    <properties>
+        <maven.compiler.source>8</maven.compiler.source>
+        <maven.compiler.target>8</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+    <dependencies>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>2.11.0</version>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>
--- a/exp3-network/src/main/java/net/lensfrex/Main.java
+++ b/exp3-network/src/main/java/net/lensfrex/Main.java
@ -0,0 +1,53 @@
+package net.lensfrex;
+
+import net.lensfrex.socket.client.Client;
+import net.lensfrex.socket.server.Server;
+import net.lensfrex.socket.common.Util;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+
+public class Main {
+    public static void main(String[] args) throws Exception {
+        System.out.println("Thread Lesson report");
+
+        if (args.length > 0) {
+            execute(args[0]);
+        } else {
+            System.out.println("Witch to run? (1server, 1client, 2)");
+            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+
+            execute(reader.readLine());
+        }
+    }
+
+    private static void execute(String option) {
+        Main main = new Main();
+
+        switch (option) {
+            case "1server":
+                main.run1Server();
+                break;
+            case "1client":
+                main.run1Client();
+                break;
+            case "2":
+                main.run2();
+                break;
+            default:
+                System.out.printf("Invalid input for '%s'%n", option);
+        }
+    }
+
+    private void run1Server() {
+        new Server().start();
+    }
+
+    private void run1Client() {
+        new Client().start();
+    }
+
+    private void run2() {
+        new URLConnectionResource().startTest();
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/URLConnectionResource.java
+++ b/exp3-network/src/main/java/net/lensfrex/URLConnectionResource.java
@ -0,0 +1,44 @@
+package net.lensfrex;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.net.URLConnection;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+public class URLConnectionResource {
+    private static final String targetSite = "https://www.gnu.org/licenses/gpl-3.0.txt";
+    public void startTest() {
+        URLConnection urlConnection;
+        try {
+            urlConnection = new URL(targetSite).openConnection();
+
+            Set<Map.Entry<String, List<String>>> headers = urlConnection.getHeaderFields().entrySet();
+
+            for (Map.Entry<String, List<String>> entry : headers) {
+                String key = entry.getKey();
+                List<String> values = entry.getValue();
+                for (String value : values) {
+                    System.out.printf("%s: %s%n", key, value);
+                }
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+            return;
+        }
+
+        System.err.println("--------------------------------");
+
+        try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream(), StandardCharsets.UTF_8))) {
+            String line = bufferedReader.readLine();
+            for (int i = 0; line != null && i < 10; i++, line = bufferedReader.readLine()) {
+                System.out.println(line);
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/client/Client.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/client/Client.java
@ -0,0 +1,216 @@
+package net.lensfrex.socket.client;
+
+import javafx.application.Application;
+import javafx.geometry.Insets;
+import javafx.geometry.Pos;
+import javafx.scene.Parent;
+import javafx.scene.Scene;
+import javafx.stage.Stage;
+
+import javafx.scene.control.*;
+import javafx.scene.layout.*;
+import net.lensfrex.socket.client.controller.ClientConnection;
+import net.lensfrex.socket.common.Common;
+import net.lensfrex.socket.common.Constant;
+import net.lensfrex.socket.common.DataPack;
+import net.lensfrex.socket.common.MessageData;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.Random;
+
+public class Client extends Application {
+    public void start() {
+        launch();
+    }
+
+    @Override
+    public void start(Stage stage) throws Exception {
+        Scene scene = new Scene(new UI().buildUI(), 515, 509);
+
+        // 主题，不想要或者网络出错的话注释掉就好了
+//        scene.getStylesheets().add(new URL("https://www.lensfrex.net/light.css").toExternalForm());
+//        scene.getStylesheets().add(new URL("https://www.lensfrex.net/dark.css").toExternalForm());
+        scene.getStylesheets().add(new URL("http://127.0.0.1/light.css").toExternalForm());
+
+        stage.setTitle("(￣﹃￣)");
+        stage.setScene(scene);
+
+        stage.show();
+    }
+}
+
+class UI {
+    private static final String[] DEFAULT_USERNAMES = {"Rex", "Red", "Ash", "Aether"};
+
+    private Pane pane;
+    private VBox rootBox;
+
+    private HBox serverControlVBox;
+    private TextField serverTextField;
+
+    private TextArea messageTextArea;
+    private HBox userControlVBox;
+    private TextField usernameTextField;
+    private Button loginButton, logoutButton;
+    private HBox messageControlVBox;
+    private TextField messageTextField;
+    private Button sendButton;
+
+    protected Parent buildUI() {
+        pane = new Pane();
+
+        rootBox = new VBox();
+        rootBox.setPadding(new Insets(10, 10, 10, 10));
+        rootBox.setSpacing(20);
+        rootBox.setPrefWidth(500);
+        rootBox.setPrefHeight(500);
+
+        messageTextArea = new TextArea("暂无消息...");
+        messageTextArea.setPrefHeight(700);
+        messageTextArea.setEditable(false);
+
+        rootBox.getChildren().addAll(serverControlPane(), userControlPane(), messageTextArea, messageControlPane());
+        pane.getChildren().addAll(rootBox);
+
+        return pane;
+    }
+
+    private HBox serverControlPane() {
+        serverControlVBox = new HBox();
+        serverControlVBox.setSpacing(10);
+        serverControlVBox.setAlignment(Pos.CENTER_LEFT);
+
+        Label serverLabel = new Label("服务器地址：");
+
+        serverTextField = new TextField("127.0.0.1:2333");
+        serverTextField.setPrefWidth(320);
+
+        serverControlVBox.getChildren().addAll(serverLabel, serverTextField);
+
+        return serverControlVBox;
+    }
+
+
+    private HBox userControlPane() {
+        userControlVBox = new HBox();
+        userControlVBox.setSpacing(10);
+        userControlVBox.setAlignment(Pos.CENTER_LEFT);
+
+        Label usernameLabel = new Label("用户名：");
+
+        String username = DEFAULT_USERNAMES[new Random().nextInt(DEFAULT_USERNAMES.length)];
+        usernameTextField = new TextField(username);
+        usernameTextField.setPrefWidth(200);
+
+        loginButton = new Button("登录");
+        loginButton.setOnAction(e -> {
+            try {
+                this.auth(Constant.OPCODE_LOGIN);
+
+                logoutButton.setDisable(false);
+                loginButton.setDisable(true);
+                serverTextField.setDisable(true);
+                usernameTextField.setDisable(true);
+                messageControlVBox.setDisable(false);
+            } catch (Exception ex) {
+                ex.printStackTrace();
+                messageTextArea.textProperty().set("登录服务器时发生错误：" + ex);
+            }
+        });
+
+        logoutButton = new Button("注销");
+        logoutButton.setDisable(true);
+        logoutButton.setOnAction(e -> {
+            try {
+                this.auth(Constant.OPCODE_LOGOUT);
+
+                logoutButton.setDisable(true);
+                loginButton.setDisable(false);
+                serverTextField.setDisable(false);
+                usernameTextField.setDisable(false);
+                messageControlVBox.setDisable(true);
+            } catch (Exception ex) {
+                ex.printStackTrace();
+                messageTextArea.textProperty().set("登录服务器时发生错误：" + ex);
+            }
+        });
+
+        userControlVBox.getChildren().addAll(usernameLabel, usernameTextField, loginButton, logoutButton);
+
+        return userControlVBox;
+    }
+
+    private void auth(byte[] opcode) throws Exception {
+        String[] address = serverTextField.getText().split(":");
+        int port = Integer.parseInt(address[1]);
+
+        ClientConnection connection = new ClientConnection(address[0], port);
+
+        byte[] data = usernameTextField.getText().getBytes(StandardCharsets.UTF_8);
+        OutputStream outputStream = connection.getOutputStream();
+
+        Common.send(data, opcode, outputStream);
+        connection.finishOutput();
+
+        InputStream inputStream = connection.getInputStream();
+        byte[] header = new byte[4];
+        inputStream.read(header);
+
+        DataPack dataPack = Common.readDataPack(inputStream);
+        MessageData messageData = MessageData.parse(dataPack.getData());
+        messageTextArea.textProperty().set(messageTextArea.getText() +
+                        String.format("\n服务器[%s]响应：%s", messageData.getIdText(), messageData.getMessageText()));
+        connection.finishInput();
+
+        connection.disconnect();
+    }
+
+    private HBox messageControlPane() {
+        messageControlVBox = new HBox();
+        messageControlVBox.setSpacing(10);
+        messageControlVBox.setAlignment(Pos.CENTER_LEFT);
+        messageControlVBox.setDisable(true);
+
+        Label usernameLabel = new Label("输入消息：");
+
+        messageTextField = new TextField();
+        messageTextField.setPrefWidth(320);
+
+        sendButton = new Button("发送");
+        sendButton.setOnAction(e -> {
+            String[] address = serverTextField.getText().split(":");
+            int port = Integer.parseInt(address[1]);
+            try {
+                ClientConnection connection = new ClientConnection(address[0], port);
+
+                MessageData messageData = new MessageData(usernameTextField.getText(), messageTextField.getText());
+
+                Common.send(messageData.toBytes(), Constant.OPCODE_SEND_MESSAGE, connection.getOutputStream());
+                connection.finishOutput();
+
+                InputStream inputStream = connection.getInputStream();
+                byte[] header = new byte[4];
+                inputStream.read(header);
+
+                DataPack dataPack = Common.readDataPack(inputStream);
+                MessageData responseData = MessageData.parse(dataPack.getData());
+                messageTextArea.textProperty().set(messageTextArea.getText() +
+                        String.format("\n服务器[%s]响应：%s", responseData.getIdText(), responseData.getMessageText()));
+                connection.finishInput();
+
+                connection.disconnect();
+            } catch (IOException ex) {
+                ex.printStackTrace();
+                messageTextArea.textProperty().set("登录服务器时发生错误：" + ex);
+            }
+        });
+
+        messageControlVBox.getChildren().addAll(usernameLabel, messageTextField, sendButton);
+
+        return messageControlVBox;
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/client/Global.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/client/Global.java
@ -0,0 +1,4 @@
+package net.lensfrex.socket.client;
+
+public class Global {
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/client/MainUI.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/client/MainUI.java
@ -0,0 +1,7 @@
+package net.lensfrex.socket.client;
+
+import javafx.scene.layout.Pane;
+
+public class MainUI extends Pane {
+
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/client/controller/ClientConnection.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/client/controller/ClientConnection.java
@ -0,0 +1,34 @@
+package net.lensfrex.socket.client.controller;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.Socket;
+
+public class ClientConnection {
+    private final Socket socket;
+
+    public ClientConnection(String host, int port) throws IOException {
+        this.socket = new Socket(host, port);
+    }
+
+    public InputStream getInputStream() throws IOException {
+        return socket.getInputStream();
+    }
+
+    public OutputStream getOutputStream() throws IOException {
+        return socket.getOutputStream();
+    }
+
+    public void disconnect() throws IOException {
+        socket.close();
+    }
+
+    public void finishOutput() throws IOException {
+        socket.shutdownOutput();
+    }
+
+    public void finishInput() throws IOException {
+        socket.shutdownInput();
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/common/Common.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/common/Common.java
@ -0,0 +1,44 @@
+package net.lensfrex.socket.common;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+
+public class Common {
+    public static DataPack readDataPack(InputStream inputStream) {
+        return readDataPack(Util.readAllData(inputStream));
+    }
+
+    public static DataPack readDataPack(byte[] dataPackBytes) {
+        return DataPack.parse(dataPackBytes);
+    }
+
+    public static int sendMessage(String id, String message, OutputStream outputStream) throws IOException {
+        MessageData messageData = new MessageData(id, message);
+
+        return sendMessage(messageData, outputStream);
+    }
+
+    public static int sendMessage(MessageData message, OutputStream outputStream) throws IOException {
+        return sendMessage(message.toBytes(), outputStream);
+    }
+
+    public static int sendMessage(byte[] data, OutputStream outputStream) throws IOException {
+        return send(data, Constant.OPCODE_SEND_MESSAGE, outputStream);
+    }
+
+    public static int send(byte[] data, byte[] opcode, OutputStream outputStream) throws IOException {
+        DataPack dataPack = new DataPack(opcode, data);
+
+        return send(dataPack, outputStream);
+    }
+
+    public static int send(DataPack dataPack, OutputStream outputStream) throws IOException {
+        outputStream.write(Constant.MAGIC_HEADER);
+        outputStream.write(dataPack.toBytes());
+
+        outputStream.flush();
+        return dataPack.getDataLength();
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/common/Constant.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/common/Constant.java
@ -0,0 +1,16 @@
+package net.lensfrex.socket.common;
+
+import java.nio.charset.StandardCharsets;
+
+public class Constant {
+    public static final int LENGTH_BYTE_SIZE = 4;
+    public static final byte[] MAGIC_HEADER = "AETH".getBytes(StandardCharsets.UTF_8);
+
+    public static final int OPCODE_LENGTH = 4;
+    public static final byte[] OPCODE_REQUEST_MESSAGE = "RMSG".getBytes(StandardCharsets.UTF_8);
+    public static final byte[] OPCODE_SEND_MESSAGE = "SMSG".getBytes(StandardCharsets.UTF_8);
+    public static final byte[] OPCODE_LOGIN = "LOGI".getBytes(StandardCharsets.UTF_8);
+    public static final byte[] OPCODE_LOGOUT = "LOGO".getBytes(StandardCharsets.UTF_8);
+
+    public static final String MESSAGE_OK = "OPERATION-OK";
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/common/DataPack.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/common/DataPack.java
@ -0,0 +1,60 @@
+package net.lensfrex.socket.common;
+
+import java.io.ByteArrayOutputStream;
+import java.io.Serializable;
+import java.util.Arrays;
+
+public class DataPack implements Serializable {
+    private final byte[] opcode;
+    private final byte[] data;
+
+    public DataPack(byte[] opcode, byte[] data) {
+        this.opcode = opcode;
+        this.data = data;
+    }
+
+    public static DataPack parse(byte[] bytes) {
+        int offset = 0;
+        byte[] opcode = Arrays.copyOfRange(bytes, offset, offset + Constant.OPCODE_LENGTH);
+
+        offset += Constant.OPCODE_LENGTH;
+        int dataLength = Util.bytesToInt32(Arrays.copyOfRange(bytes, offset, offset + Constant.LENGTH_BYTE_SIZE));
+
+        offset += Constant.LENGTH_BYTE_SIZE;
+        byte[] data = Arrays.copyOfRange(bytes, offset, offset + dataLength);
+
+        return new DataPack(opcode, data);
+    }
+
+    public byte[] toBytes() {
+        try {
+            int totalLength = Constant.OPCODE_LENGTH + Constant.LENGTH_BYTE_SIZE + data.length;
+            ByteArrayOutputStream stream = new ByteArrayOutputStream(totalLength);
+
+            stream.write(opcode);
+            stream.write(Util.int32ToBytes(data.length));
+            stream.write(data);
+
+            return stream.toByteArray();
+        } catch (Exception e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+
+    public byte[] getOpcode() {
+        return opcode;
+    }
+
+    public byte[] getData() {
+        return data;
+    }
+
+    public int getTotalLength() {
+        return Constant.OPCODE_LENGTH + Constant.LENGTH_BYTE_SIZE + data.length;
+    }
+
+    public int getDataLength() {
+        return data.length;
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/common/MessageData.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/common/MessageData.java
@ -0,0 +1,80 @@
+package net.lensfrex.socket.common;
+
+import java.io.ByteArrayOutputStream;
+import java.io.Serializable;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+
+public class MessageData implements Serializable {
+    private final byte[] id;
+    private final byte[] messageData;
+
+    public MessageData(byte[] id, byte[] messageData) {
+        this.id = id;
+        this.messageData = messageData;
+    }
+
+    public MessageData(String id, String messageData) {
+        this.id = id.getBytes(StandardCharsets.UTF_8);
+        this.messageData = messageData.getBytes(StandardCharsets.UTF_8);
+    }
+
+    public static MessageData parse(byte[] data) {
+        int offset = 0;
+        int idLength = Util.bytesToInt32(Arrays.copyOfRange(data, offset, offset + Constant.LENGTH_BYTE_SIZE));
+
+        offset += Constant.LENGTH_BYTE_SIZE;
+        byte[] id = Arrays.copyOfRange(data, offset, offset + idLength);
+
+        offset += idLength;
+        int messageDataLength = Util.bytesToInt32(Arrays.copyOfRange(data, offset, offset + Constant.LENGTH_BYTE_SIZE));
+
+        offset += Constant.LENGTH_BYTE_SIZE;
+        byte[] messageData = Arrays.copyOfRange(data, offset, offset + messageDataLength);
+
+        return new MessageData(id, messageData);
+    }
+
+    public byte[] toBytes() {
+        try {
+            int byteSize = Constant.LENGTH_BYTE_SIZE * 2 + id.length + messageData.length;
+            ByteArrayOutputStream stream = new ByteArrayOutputStream(byteSize);
+
+            stream.write(Util.int32ToBytes(id.length));
+            stream.write(id);
+            stream.write(Util.int32ToBytes(messageData.length));
+            stream.write(messageData);
+
+            return stream.toByteArray();
+        } catch (Exception e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+
+    public byte[] getId() {
+        return id;
+    }
+
+    public String getIdText() {
+        return new String(id);
+    }
+
+    public byte[] getMessageData() {
+        return messageData;
+    }
+
+    public String getMessageText() {
+        return new String(messageData);
+    }
+
+    @Override
+    public String toString() {
+        return "MessageData{" +
+                "idLength=" + id.length +
+                ", id='" + new String(id) +
+                "', messageLength=" + messageData.length +
+                ", messageData='" + new String(messageData) +
+                ";}";
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/common/User.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/common/User.java
@ -0,0 +1,36 @@
+package net.lensfrex.socket.common;
+
+import java.util.Objects;
+
+public class User {
+    private final String id;
+
+    public User(String id) {
+        this.id = id;
+    }
+
+    public User(byte[] id) {
+        this.id = new String(id);
+    }
+
+    public String getId() {
+        return id;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        User user = (User) o;
+        return id.equals(user.id);
+    }
+
+    public boolean equals(String id) {
+        return this.id.equals(id);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id);
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/common/Util.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/common/Util.java
@ -0,0 +1,66 @@
+package net.lensfrex.socket.common;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Random;
+
+public class Util {
+    private static final char[] alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
+    private static final Random random = new Random();
+
+    public static String randomString(int length) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < length; i++) {
+            sb.append(alphabet[random.nextInt(alphabet.length)]);
+        }
+
+        return sb.toString();
+    }
+
+    public static int bytesToInt32(byte[] bytes) {
+        int result = 0;
+        for (int i = 0; i < 4; i++) {
+            int shift = (3 - i) * 8;
+            result += (bytes[i] & 0xFF) << shift;
+        }
+
+        return result;
+    }
+
+    public static byte[] int32ToBytes(int i) {
+        byte[] result = new byte[4];
+        result[0] = (byte) ((i >> 24) & 0xFF);
+        result[1] = (byte) ((i >> 16) & 0xFF);
+        result[2] = (byte) ((i >> 8) & 0xFF);
+        result[3] = (byte) (i & 0xFF);
+
+        return result;
+    }
+
+    public static byte[] readAllData(InputStream inputStream) {
+        return readAllData(inputStream, 5);// read every 5kb in default
+    }
+
+    public static byte[] readAllData(InputStream inputStream, int byteAllocation) {
+        try {
+            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+            byte[] bytes = new byte[1024 * byteAllocation];
+
+            while(true) {
+                int length = inputStream.read(bytes);
+                if (length == -1) {
+                    break;
+                }
+                byteArrayOutputStream.write(bytes, 0, length);
+            }
+
+            byteArrayOutputStream.flush();
+
+            return byteArrayOutputStream.toByteArray();
+        } catch (Exception e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+}
--- a/exp3-network/src/main/java/net/lensfrex/socket/server/Server.java
+++ b/exp3-network/src/main/java/net/lensfrex/socket/server/Server.java
@ -0,0 +1,118 @@
+package net.lensfrex.socket.server;
+
+import net.lensfrex.socket.common.*;
+
+import java.io.*;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.Arrays;
+import java.util.HashSet;
+
+public class Server {
+    private static boolean stop = false;
+
+    public void start() {
+        Server.stop = false;
+
+        try (ServerSocket serverSocket = new ServerSocket(2333)) {
+            while (!stop) {
+                // Start a new thread to service more than one client
+                new ServerThread(serverSocket.accept()).start();
+            }
+        } catch (Exception e) {
+            System.err.println("Some exception happened: " + e);
+        }
+    }
+
+    public void stop() {
+        Server.stop = true;
+    }
+}
+
+class ServerThread extends Thread {
+    private static final String SERVER_ID = "MASTER-SERVER";
+    
+    private static final HashSet<User> onlineUsers = new HashSet<>();
+
+    private final Socket socket;
+
+    public ServerThread(Socket socket) {
+        this.socket = socket;
+    }
+
+    @Override
+    public void run() {
+        try (InputStream inputStream = socket.getInputStream(); OutputStream outputStream = socket.getOutputStream()) {
+            byte[] clientMagicHeader = new byte[Constant.MAGIC_HEADER.length];
+            if (inputStream.read(clientMagicHeader) == -1) {
+                return;
+            }
+
+            this.executeAction(inputStream, outputStream);
+            socket.shutdownOutput();
+            socket.shutdownInput();
+            socket.close();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private void executeAction(InputStream inputStream, OutputStream outputStream) throws IOException {
+        DataPack dataPack = Common.readDataPack(inputStream);
+        byte[] opcode = dataPack.getOpcode();
+
+        if (Arrays.equals(Constant.OPCODE_LOGIN, opcode)) {
+            this.login(new String(dataPack.getData()));
+            Common.sendMessage(SERVER_ID, Constant.MESSAGE_OK, outputStream);
+        } else if (Arrays.equals(Constant.OPCODE_LOGOUT, opcode)) {
+            this.logout(new String(dataPack.getData()));
+            Common.sendMessage(SERVER_ID, Constant.MESSAGE_OK, outputStream);
+        } else if (Arrays.equals(Constant.OPCODE_REQUEST_MESSAGE, opcode)) {
+            this.sendRandomMessage(outputStream);
+        } else if (Arrays.equals(Constant.OPCODE_SEND_MESSAGE, opcode)) {
+            String receivedMessage = this.receiveMessage(dataPack);
+            String responseMessage = String.format("Receive message '%s'",  receivedMessage);
+
+            Common.sendMessage(SERVER_ID, responseMessage, outputStream);
+        }
+    }
+
+    private void login(String id) {
+        onlineUsers.add(new User(id));
+
+        System.out.printf("User '%s' login.%n", id);
+    }
+
+    private void logout(String id) {
+        onlineUsers.remove(new User(id));
+
+        System.out.printf("User '%s' logout.%n", id);
+    }
+
+    private void sendRandomMessage(OutputStream outputStream) throws IOException {
+        this.sendMessage(Util.randomString(64), outputStream);
+    }
+
+    private void sendMessage(String messageText, OutputStream outputStream) throws IOException {
+        Common.sendMessage(SERVER_ID, messageText, outputStream);
+    }
+
+    private String receiveMessage(DataPack dataPack) {
+        byte[] data = dataPack.getData();
+        MessageData messageData = MessageData.parse(data);
+
+        User user = new User(messageData.getIdText());
+
+        if (!onlineUsers.contains(user)) {
+            String message = "User " + user.getId() + " is not online, but send a message.";
+            System.err.println(message);
+
+            return message;
+        }
+
+        System.out.printf("Receive message '%s' from: '%s'%n", messageData.getMessageText(), user.getId());
+        System.out.println("----------------");
+
+        return messageData.getMessageText();
+    }
+}
--- a/pom.xml
+++ b/pom.xml
@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>net.lensfrex</groupId>
+    <artifactId>lesson</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>pom</packaging>
+    <modules>
+        <module>exp1-oop</module>
+        <module>exp2-thread</module>
+        <module>exp3-network</module>
+    </modules>
+
+    <properties>
+        <maven.compiler.source>8</maven.compiler.source>
+        <maven.compiler.target>8</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>
--- a/src/main/java/net/lensfrex/Main.java
+++ b/src/main/java/net/lensfrex/Main.java
@ -0,0 +1,7 @@
+package net.lensfrex;
+
+public class Main {
+    public static void main(String[] args) {
+        System.out.println("Hello world!");
+    }
+}