* Access to the `Connection` that carries the request.

### Rewriting Requests

Interceptors can add, remove, or replace request headers. They can also transform the body of those requests that have one. For example, you can use an application interceptor to add request body compression if you're connecting to a webserver known to support it.

```java

   * occur when using {@link CacheBuilder#weakKeys}, {@link CacheBuilder#weakValues}, or {@link
   * CacheBuilder#softValues}.
   */
  COLLECTED {
    @Override
    boolean wasEvicted() {
      return true;
    }
  },

  /**
   * The entry's expiration timestamp has passed. This can occur when using {@link

# Custom Response Classes - File, HTML, Redirect, Streaming, etc.

There are several custom response classes you can use to create an instance and return them directly from your *path operations*.

Read more about it in the [FastAPI docs for Custom Response - HTML, Stream, File, others](https://fastapi.tiangolo.com/advanced/custom-response/).

You can import them directly from `fastapi.responses`:

```python
from fastapi.responses import (
    FileResponse,

under the License.
-->

<!--
 | This is the toolchains file for Maven. It can be specified at two levels:
 |
 |  1. User Level. This toolchains.xml file provides configuration for a single user,
 |                 and is normally provided in ${user.home}/.m2/toolchains.xml.
 |
 |                 NOTE: This location can be overridden with the CLI option:
 |
 |                 -t /path/to/user/toolchains.xml
 |

/// tip

You can set a dependency override for a dependency used anywhere in your **FastAPI** application.

The original dependency could be used in a *path operation function*, a *path operation decorator* (when you don't use the return value), a `.include_router()` call, etc.

FastAPI will still be able to override it.

///

/*
 * © 2025 CodeLibs, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of

     *
     * @return minimum size in bytes for compression to be beneficial
     */
    int getMinCompressionSize();

    /**
     * Gets the maximum data size that can be compressed in a single operation.
     *
     * @return maximum size in bytes that can be compressed
     */
    int getMaxCompressionSize();

    /**
     * Gets a human-readable name for the compression algorithm.
     *

But this way we can focus on how the **Dependency Injection** system works.

### Create a dependency, or "dependable" { #create-a-dependency-or-dependable }

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

# Declare Request Example Data { #declare-request-example-data }

You can declare examples of the data your app can receive.

Here are several ways to do it.

## Extra JSON Schema data in Pydantic models { #extra-json-schema-data-in-pydantic-models }

You can declare `examples` for a Pydantic model that will be added to the generated JSON Schema.

//// tab | Pydantic v2

{* ../../docs_src/schema_extra_example/tutorial001_py310.py hl[13:24] *}

So, you can look for that specific exception inside the dependency with `except SomeException`.

In the same way, you can use `finally` to make sure the exit steps are executed, no matter if there was an exception or not.

{* ../../docs_src/dependencies/tutorial007.py hl[3,5] *}

## Sub-dependencies with `yield` { #sub-dependencies-with-yield }