{* ../../docs_src/middleware/tutorial001_py39.py hl[8:9,11,14] *}

/// tip | Tipp

Beachten Sie, dass benutzerdefinierte proprietäre Header hinzugefügt werden können <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">unter Verwendung des `X-`-Präfixes</a>.

   */
  @SuppressWarnings("unchecked")
  public static <T extends @Nullable Object> Collector<T, ?, T> onlyElement() {
    return (Collector) ONLY_ELEMENT;
  }

  /**
   * This atrocity is here to let us report several of the elements in the stream if there were more
   * than one, not just two.
   */
  @SuppressWarnings("EmptyList") // ImmutableList doesn't support nullable element types

    }

    /*
     * We need the top SIGNIFICAND_BITS + 1 bits, including the "implicit" one bit. To make rounding
     * easier, we pick out the top SIGNIFICAND_BITS + 2 bits, so we have one to help us round up or
     * down. twiceSignifFloor will contain the top SIGNIFICAND_BITS + 2 bits, and signifFloor the
     * top SIGNIFICAND_BITS + 1.
     *

## Date

2025-08-06

## Context

Our codebase uses `null` extensively to represent an absence of value or optionality of the argument.
We utilize nullness annotations in Java code and somewhat rely on IDE warnings to guide us.
However, the Java code we have is not fully annotated, which causes several consequences:
* IDE warnings can be misleading
* Redundant null checks may increase binary size, hurt performance, and increase cognitive load for readers

 * classes and the classes they depend on. The classes are not relocated, they all
 * remain in their original namespace. This reduces the final Gradle distribution
 * size and makes us more conscious of which parts of a library we really need.
 *
 * WARNING: if you decide to do the minification by hand, make sure that you cover all paths of loading classes:

   * with a warning under recent JVMs), or it may fall back even further to
   * AtomicReferenceFieldUpdaterAtomicHelper, which would fail with a similar problem to
   * VarHandleAtomicHelperMaker, forcing us all the way to SynchronizedHelper.
   *
   * Additionally, it seems that nestmates do not help with runtime reflection under *Android*, even

   * they can return ASCII characters that match real hostnames.
   */
  private fun String.asciiToLowercase(): String =
    when {
      isAscii() -> lowercase(Locale.US) // This is an ASCII string.
      else -> this
    }

  /** Returns true if the [String] is ASCII encoded (0-127). */
  private fun String.isAscii() = length == utf8Size().toInt()

  /**

    private final Executor adapterExecutor;

    // The execution list to hold our listeners.
    private final ExecutionList executionList = new ExecutionList();

    // This allows us to only start up a thread waiting on the delegate future when the first
    // listener is added.
    private final AtomicBoolean hasListeners = new AtomicBoolean(false);

    // The delegate future.

* `5xx` 상태 코드는 서버 오류에 사용됩니다. 이것들을 직접 사용할 일은 거의 없습니다. 응용 프로그램 코드나 서버의 일부에서 문제가 발생하면 자동으로 이들 상태 코드 중 하나를 반환합니다.

/// tip | 팁

각각의 상태 코드와 이들이 의미하는 내용에 대해 더 알고싶다면 <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Status" class="external-link" target="_blank"><abbr title="Mozilla Developer Network">MDN</abbr> HTTP 상태 코드에 관한 문서</a> 를 확인하십시오.

///

## 이름을 기억하는 쉬운 방법

상기 예시 참고:

# WebSockets { #websockets }

Você pode usar <a href="https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API" class="external-link" target="_blank">WebSockets</a> com **FastAPI**.

## Instale `websockets` { #install-websockets }

Garanta que você criou um [ambiente virtual](../virtual-environments.md){.internal-link target=_blank}, o ativou e instalou o `websockets` (uma biblioteca Python que facilita o uso do protocolo "WebSocket"):

<div class="termy">