This can be very useful for setting up **resources** that you need to use for the whole app, and that are **shared** among requests, and/or that you need to **clean up** afterwards. For example, a database connection pool, or loading a shared machine learning model.

## Use Case

Let's start with an example **use case** and then see how to solve it with this.

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 *
 * Typically instances of this class are created, connected and exercised automatically by the HTTP
 * client. Applications may use this class to monitor HTTP connections as members of a
 * [connection pool][ConnectionPool].
 *
 * Do not confuse this class with the misnamed `HttpURLConnection`, which isn't so much a connection
 * as a single request/response exchange.
 *
 * ## Modern TLS
 *

Webargs is a tool that was made to provide that on top of several frameworks, including Flask.

It uses Marshmallow underneath to do the data validation. And it was created by the same developers.

It's a great tool and I have used it a lot too, before having **FastAPI**.

/// info

* Adds configuration for AWS endpoint fine control: ([#72245](https://github.com/kubernetes/kubernetes/pull/72245), [@ampsingram](https://github.com/ampsingram))
    * OverrideEndpoints bool Set to true to allow custom endpoints
    * ServiceDelimiter string Delimiter to use to separate overridden services (multiple services) Defaults to "&"

```

////

//// tab | Python 3.8+

```Python hl_lines="9-13  15-16  20"
{!> ../../docs_src/response_model/tutorial003_01.py!}
```

////

Damit erhalten wir Tool-Unterstützung, vom Editor und mypy, da dieser Code hinsichtlich der Typen korrekt ist, aber wir erhalten auch die Datenfilterung von FastAPI.

Wie funktioniert das? Schauen wir uns das mal an. 🤓

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    This is a reference for the Maven Toolchains descriptor.
    <p>The default location for the toolchains file is {@code ~/.m2/toolchains.xml}
    <p>A Toolchain is a preconfigured object that Maven plugins can use for tool configuration retrieval (location and other information).
    <p>The <a href="/plugins/maven-toolchains-plugin/">toolchains-plugin</a> can read available toolchains on the user's computer

/// note

It doesn't matter what you type in the form, it won't work yet. But we'll get there.

///

This is of course not the frontend for the final users, but it's a great automatic tool to document interactively all your API.

It can be used by the frontend team (that can also be yourself).

It can be used by third party applications and systems.

 *
 * Copy WireSharkKeyLoggerListener to your test code to use in development.
 *
 * This logs TLSv1.2 on a JVM (OpenJDK 11+) without any additional code.  For TLSv1.3
 * an existing external tool is required.
 *
 * See https://stackoverflow.com/questions/61929216/how-to-log-tlsv1-3-keys-in-jsse-for-wireshark-to-decode-traffic
 *
 * Steps to run in your own code
 *