Par défaut, **FastAPI** convertirait automatiquement cette valeur de retour en JSON en utilisant le `jsonable_encoder` expliqué dans [JSON Compatible Encoder](../tutorial/encoder.md){.internal-link target=_blank}.

Ensuite, en arrière-plan, il mettra ces données JSON-compatible (par exemple un `dict`) à l'intérieur d'un `JSONResponse` qui sera utilisé pour envoyer la réponse au client.

 *
 * <p>Each request is associated with a {@link ProtoSession} that contains the configuration
 * and context necessary for request processing, including:
 * <ul>
 *   <li>User and system properties for interpolation</li>
 *   <li>Session start time information</li>
 *   <li>Project directory structures</li>
 * </ul>
 *
 * <p>Requests can optionally carry trace information through {@link RequestTrace} to support:
 * <ul>

       <title>Incubating APIs</title>
       <link xmlns:xslthl="http://xslthl.sf.net" rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,400i,700">
       <meta xmlns:xslthl="http://xslthl.sf.net" content="width=device-width, initial-scale=1" name="viewport">

   * given value. If multiple parameters with the same attributes are necessary use {@link
   * #withParameters(String, Iterable)}. Prefer {@link #withCharset} for setting the {@code charset}
   * parameter when using a {@link Charset} object.
   *
   * @throws IllegalArgumentException if either {@code attribute} or {@code value} is invalid
   */

  /**
   * An instance created in {@link #readObject} to be returned from {@link #readResolve}. This field
   * is used only by those methods, and it is never set in a "normal" instance.
   *
   * <p>This class needs to write deserialized data into fields that are {@code final transient}.
   * Such writes will become impossible to perform in {@link #readObject} after JEP 500. Instead, we

本例没有实现回调本身（只是一行代码），只有文档部分。

/// tip | 提示

实际的回调只是 HTTP 请求。

实现回调时，要使用 <a href="https://www.encode.io/httpx/" class="external-link" target="_blank">HTTPX</a> 或 <a href="https://requests.readthedocs.io/" class="external-link" target="_blank">Requests</a>。

///

## 编写回调文档代码

应用不执行这部分代码，只是用它来*记录 外部 API* 。

但，您已经知道用 **FastAPI** 创建自动 API 文档有多简单了。

    } else if (superString != null) {
      return resultString + superString;
    }
    return null;
  }

  /**
   * An {@link AbstractTransformFuture} that delegates to an {@link AsyncFunction} and {@link
   * #setFuture(ListenableFuture)}.
   */
  private static final class AsyncTransformFuture<
          I extends @Nullable Object, O extends @Nullable Object>

 *
 * <p>If the resulting URLs are inserted into an HTML or XML document, they will require additional
 * escaping with {@link com.google.common.html.HtmlEscapers} or {@link
 * com.google.common.xml.XmlEscapers}.
 *
 * @author David Beaumont
 * @author Chris Povirk
 * @since 15.0
 */
@GwtCompatible
public final class UrlEscapers {
  private UrlEscapers() {}

If you have a new feature idea, please build it in an external library. There are
[many libraries][works_with_okhttp] that sit on top or hook in via existing APIs. If you build
something that integrates with OkHttp, tell us so that we can link it!

Before code can be accepted all contributors must complete our
[Individual Contributor License Agreement (CLA)][cla].


Code Contributions
------------------

If you have a new feature idea, please build it in an external library. There are
[many libraries][works_with_okhttp] that sit on top or hook in via existing APIs. If you build
something that integrates with OkHttp, tell us so that we can link it!

Before code can be accepted all contributors must complete our
[Individual Contributor License Agreement (CLA)][cla].


Code Contributions
------------------