*
   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated. Instead,
   * use the {@code ArrayList} {@linkplain ArrayList#ArrayList() constructor} directly, taking
   * advantage of <a
   * href="https://docs.oracle.com/javase/tutorial/java/generics/genTypeInference.html#type-inference-instantiation">"diamond"
   * syntax</a>.
   */
  @GwtCompatible(serializable = true)

Remember that dependencies can have sub-dependencies?

`get_current_user` will have a dependency with the same `oauth2_scheme` we created before.

The same as we were doing before in the *path operation* directly, our new dependency `get_current_user` will receive a `token` as a `str` from the sub-dependency `oauth2_scheme`:

//// tab | Python 3.10+

```Python hl_lines="25"
{!> ../../docs_src/security/tutorial002_an_py310.py!}

import okhttp3.internal.platform.Platform

/**
 * Modern reflection based SocketAdapter for Conscrypt class SSLSockets.
 *
 * This is used directly for providers where class name is known e.g. the Google Play Provider
 * but we can't compile directly against it, or in fact reliably know if it is registered and
 * on classpath.
 */

import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@link Map#putIfAbsent}. Can't be invoked directly; please see
 * {@link com.google.common.collect.testing.MapTestSuiteBuilder}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.

# Templates

You can use any template engine you want with **FastAPI**.

A common choice is Jinja2, the same one used by Flask and other tools.

There are utilities to configure it easily that you can use directly in your **FastAPI** application (provided by Starlette).

## Install dependencies

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and install `jinja2`:

<div class="termy">

## Import `Field`

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

Notice that `Field` is imported directly from `pydantic`, not from `fastapi` as are all the rest (`Query`, `Path`, `Body`, etc).

///

## Declare model attributes

You can then use `Field` with model attributes:

You can declare a parameter in a *path operation function* or dependency function with the type `BackgroundTasks`, and then you can use it to schedule the execution of background tasks after the response is sent.

You can import it directly from `fastapi`:

```python
from fastapi import BackgroundTasks
```

things you should know about contributing:

1.  API changes require discussion, use cases, etc. Code comes later.
2.  Pull requests are great for small fixes for bugs, documentation, etc.
3.  Pull requests are not merged directly into the master branch.
4.  Code contributions require signing a Google CLA.

API changes
-----------

We make changes to Guava's public [APIs][], including adding new APIs, very

But `OAuth2PasswordRequestForm` is just a class dependency that you could have written yourself, or you could have declared `Form` parameters directly.

But as it's a common use case, it is provided by **FastAPI** directly, just to make it easier.

///

### Use the form data

/// tip

import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@link Map#forEach}. Can't be invoked directly; please see
 * {@link com.google.common.collect.testing.MapTestSuiteBuilder}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.