Dependency Injection Framework

This is a simple example of a dependency injection framework in Kotlin that supports both constructor injection and property injection. It demonstrates how to use the framework in your project.

Improvements needed

Creates the whole graph at startup, that is very inefficient. It should create the graph on demand, when a class is requested.
Uses reflection. This is slow and error-prone. It should use code generation instead.
To publish the library to Maven Central.
...many other things...

Usage

To use the dependency injection framework, follow these steps:

Create an instance of the Injector class in your main function:

fun main(args: Array<String>) {
    val injector = Injector()
    // ...
}

Use the inject method of the Injector class to register the desired package for component scanning. For example:

injector.inject("com.example_package")

Define your classes with dependencies and annotate them with the @Inject annotation on the constructor or properties. Here's an example:

class CoffeeMaker @Inject constructor(private val pump: Pump) {
    @Inject
    lateinit var heater: Heater

    fun makeCoffee() {
        pump.drip()
        heater.heat()
        System.out.println("Coffee!!!")
    }
}

class Pump @Inject constructor() {
    fun drip(): Unit {}
}

class Heater @Inject constructor() {
    fun heat(): Unit {}
}

Finally, use the get method of the Injector class to obtain an instance of the desired class. For example:

val maker = injector.get<CoffeeMaker>()
maker.makeCoffee()

Classes

Injector

The Injector class is responsible for managing dependencies and providing instances of the requested classes. It provides the following methods:

inject(packageName: String): Scans the given package for classes with the @Inject annotation and registers them for dependency injection.
get<T>(): T: Retrieves an instance of the requested class T from the injector.

@Inject Annotation

The @Inject annotation is used to mark constructors and properties that have dependencies. The framework uses this annotation to identify the constructors that need to be invoked and properties that need to be injected.

License

This project is licensed under the MIT License.

pietmau / DiProject