how to build an api

pom.xml

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+<?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>ch.heig.dai</groupId>
+    <artifactId>ch.heig.dai</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <version>3.6.0</version>
+                <configuration>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <archive>
+                        <manifest>
+                            <mainClass>ch.heig.dai.Main</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>make-assembly</id>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.javalin</groupId>
+            <artifactId>javalin</artifactId>
+            <version>5.6.3</version>
+        </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-simple</artifactId>
+            <version>2.0.7</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>2.15.0</version>
+        </dependency>
+    </dependencies>
+
+</project>

src/main/java/ch/heig/dai/Main.java

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+package ch.heig.dai;
+
+import io.javalin.*;
+
+public class Main {
+    public static void main(String[] args) {
+
+        Javalin app = Javalin.create().start(7000);
+
+        UserController userController = new UserController();
+        app.get("/api/users", userController::getAll);
+        app.get("/api/users/{id}", userController::getOne);
+        app.post("/api/users/", userController::create);
+        app.put("/api/users/{id}", userController::update);
+        app.delete("/api/users/{id}", userController::delete);
+    }
+}

src/main/java/ch/heig/dai/User.java

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+package ch.heig.dai;
+
+public class User {
+    public String firstName = "";
+    public String lastName = "";
+
+    public User() { }
+
+    public User(String firstName, String lastName) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+}

src/main/java/ch/heig/dai/UserController.java

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+package ch.heig.dai;
+
+import io.javalin.http.Context;
+import java.util.concurrent.ConcurrentHashMap;
+
+class UserController {
+
+    // "Database" of users
+    // Since the server is multi-threaded, we need to use a thread-safe data structure
+    // such as ConcurrentHashMap or HashMap
+    private ConcurrentHashMap<Integer, User> users = new ConcurrentHashMap<Integer, User>();
+    private int lastId = 0;
+
+    public UserController() {
+        // Add some users to the "database"
+        users.put(++lastId, new User("Anita", "Braig"));
+        users.put(++lastId, new User("Bill", "Ding"));
+        users.put(++lastId, new User("Chris P.", "Bacon"));
+    }
+
+    public void getOne(Context ctx) {
+        int id = Integer.parseInt(ctx.pathParam("id"));
+        ctx.json(users.get(id));
+    }
+
+    public void getAll(Context ctx) {
+        ctx.json(users);
+    }
+
+    public void create(Context ctx) {
+        User user = ctx.bodyAsClass(User.class);
+        users.put(++lastId, user);
+        ctx.status(201);
+    }
+
+    public void delete(Context ctx) {
+        int id = Integer.parseInt(ctx.pathParam("id"));
+        users.remove(id);
+        ctx.status(204);
+    }
+
+    public void update(Context ctx) {
+        int id = Integer.parseInt(ctx.pathParam("id"));
+        User user = ctx.bodyAsClass(User.class);
+        users.put(id, user);
+        ctx.status(200);
+    }
+
+}