It is designed to be very simple to use, and to make it very easy for any developer to integrate other components with **FastAPI**.

## What is "Dependency Injection" { #what-is-dependency-injection }

## Code size { #code-size }

This example might seem verbose. Keep in mind that we are mixing security, data models, utility functions and *path operations* in the same file.

But here's the key point.

The security and dependency injection stuff is written once.

import jakarta.annotation.PostConstruct;
import jakarta.annotation.PreDestroy;
import jakarta.annotation.Resource;

/**
 * A container implementation that manages the lifecycle and dependency injection of components
 * in a crawler application. This container supports both singleton and prototype component
 * instantiation patterns.
 *
 * <p>The container provides mechanisms for:
 * <ul>

     */
    public RelatedQueryHelper() {
        super();
    }

    /**
     * Initializes the RelatedQueryHelper after dependency injection is complete.
     * This method is called automatically by the dependency injection framework
     * and loads the initial related query configurations.
     */
    @PostConstruct
    public void init() {
        if (logger.isDebugEnabled()) {

* Any keyword arguments that should be passed to the task function (`message="some notification"`).

## Dependency Injection { #dependency-injection }

Using `BackgroundTasks` also works with the dependency injection system, you can declare a parameter of type `BackgroundTasks` at multiple levels: in a *path operation function*, in a dependency (dependable), in a sub-dependency, etc.

It achieves something somewhat similar to what can be done with Flask-apispec.

It has an integrated dependency injection system, inspired by Angular 2. It requires pre-registering the "injectables" (like all the other dependency injection systems I know), so, it adds to the verbosity and code repetition.

        super();
    }

    /** Logger instance for this class */
    private static final Logger logger = LogManager.getLogger(FessFileTransformer.class);

    /**
     * Initializes the transformer after dependency injection.
     * Sets up the Fess configuration and data serializer components.
     */
    @PostConstruct
    public void init() {
        if (logger.isDebugEnabled()) {

    }

    /**
     * Registers this creator with the dictionary manager upon initialization.
     * This method is annotated with {@link PostConstruct} to be executed after
     * dependency injection is complete.
     */
    @PostConstruct
    public void register() {
        if (logger.isInfoEnabled()) {
            logger.info("Load {}", this.getClass().getSimpleName());
        }

### Dependency Injection { #dependency-injection }

FastAPI includes an extremely easy to use, but extremely powerful <abbr title='also known as "components", "resources", "services", "providers"'><strong>Dependency Injection</strong></abbr> system.

* Even dependencies can have dependencies, creating a hierarchy or **"graph" of dependencies**.

    /** Factory for creating and managing ingesters */
    private IngestFactory ingestFactory = null;

    /**
     * Initializes the processor after dependency injection.
     * Sets up the ingest factory if available in the component system.
     */
    @PostConstruct
    public void init() {
        if (ComponentUtil.hasIngestFactory()) {