# Dependencies { #dependencies }

**FastAPI** has a very powerful but intuitive **<abbr title="also known as components, resources, providers, services, injectables">Dependency Injection</abbr>** system.

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 }

    @Timeout(value = 1, unit = TimeUnit.SECONDS) // Very short timeout
    void testBroadcastTimeout() {
        // Configure for broadcast-only resolution with very short timeout
        when(mockConfig.getResolveOrder()).thenReturn(Arrays.asList(ResolverType.RESOLVER_BCAST));
        when(mockConfig.getNetbiosSoTimeout()).thenReturn(50); // Very short
        when(mockConfig.getNetbiosRetryCount()).thenReturn(1);

That should make more sense now. ✨

All that is what powers FastAPI (through Starlette) and what makes it have such an impressive performance.

## Very Technical Details { #very-technical-details }

/// warning

You can probably skip this.

These are very technical details of how **FastAPI** works underneath.

They are, more or less, at opposite ends, complementing each other.

Requests has a very simple and intuitive design, it's very easy to use, with sensible defaults. But at the same time, it's very powerful and customizable.

That's why, as said in the official website:

> Requests is one of the most downloaded Python packages of all time

The way you use it is very simple. For example, to do a `GET` request, you would write:

```Python

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

It declares an optional query parameter `q` as a `str`, and then it just returns it.

This is quite simple (not very useful), but will help us focus on how the sub-dependencies work.

## Second dependency, "dependable" and "dependant" { #second-dependency-dependable-and-dependant }

That's what all the systems with "login with Facebook, Google, X (Twitter), GitHub" use underneath.

### OAuth 1 { #oauth-1 }

There was an OAuth 1, which is very different from OAuth2, and more complex, as it included direct specifications on how to encrypt the communication.

It is not very popular or used nowadays.

OAuth2 doesn't specify how to encrypt the communication, it expects you to have your application served with HTTPS.

/// tip

# GraphQL { #graphql }

As **FastAPI** is based on the **ASGI** standard, it's very easy to integrate any **GraphQL** library also compatible with ASGI.

You can combine normal FastAPI *path operations* with GraphQL on the same application.

/// tip

**GraphQL** solves some very specific use cases.

It has **advantages** and **disadvantages** when compared to common **web APIs**.

   */
  @IgnoreJRERequirement // Users will use this only if they're already using streams.
  public static ImmutableLongArray copyOf(LongStream stream) {
    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
    long[] array = stream.toArray();
    return (array.length == 0) ? EMPTY : new ImmutableLongArray(array);
  }

  /**

   *
   * @since 22.0 (but only since 33.4.0 in the Android flavor)
   */
  public static ImmutableIntArray copyOf(IntStream stream) {
    // Note this uses very different growth behavior from copyOf(Iterable) and the builder.
    int[] array = stream.toArray();
    return (array.length == 0) ? EMPTY : new ImmutableIntArray(array);
  }

  /**

        value = "${spaces}";
        assertEquals("   ", ResourceUtil.resolve(value));

        // Test long property name
        System.setProperty("very.long.property.name.with.many.dots", "long");
        value = "${very.long.property.name.with.many.dots}";
        assertEquals("long", ResourceUtil.resolve(value));

        // Test multiple occurrences of same variable