Dependency Injection

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>at.aydin.academy</groupId>
        <artifactId>01dependencyinjection-pair</artifactId>
        <version>1.0.0</version>
        <relativePath>../pom.xml</relativePath>
    </parent>
    <artifactId>di-modern</artifactId>
    <packaging>jar</packaging>
    <name>DI Modern</name>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

package at.aydin.lab.di.modern;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DiModernApplication {
    public static void main(String[] args) {
        SpringApplication.run(DiModernApplication.class, args);
    }
}

package at.aydin.lab.di.modern;

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class GreetingRunner implements CommandLineRunner {
    private final GreetingPort greetingPort;
    // Design Pattern: Constructor Injection
    // Zweck: Abhängigkeiten sind sichtbar, unveränderlich und leicht testbar.
    public GreetingRunner(GreetingPort greetingPort) {
        this.greetingPort = greetingPort;
    }

    @Override
    public void run(String ... args) {
        System.out.println(greetingPort.greet("Aydin"));
    }
}

package at.aydin.lab.di.modern;

// Design Pattern: Port (Hexagonal Architecture)
// Zweck: Die Anwendung hängt von einem fachlichen Vertrag statt einer konkreten Implementierung ab.
public interface GreetingPort {
    String greet(String name);
}

package at.aydin.lab.di.modern;

import org.springframework.stereotype.Service;

@Service
public class GermanGreetingService implements GreetingPort {
    @Override
    public String greet(String name) {
        return "Willkommen, " + name + "!";
    }
}

package at.aydin.lab.di.modern;

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

class GermanGreetingServiceTest {
    @Test
    void greetsUser() {
        assertEquals("Willkommen, Test!", new GermanGreetingService().greet("Test"));
    }
}