The OpenAPI schema is what powers the two interactive documentation systems included.

And there are dozens of alternatives, all based on OpenAPI. You could easily add any of those alternatives to your application built with **FastAPI**.

You could also use it to generate code automatically, for clients that communicate with your API. For example, frontend, mobile or IoT applications.

    return new WeakReference<>(shadowLoader);
  }

  /*
   * TODO(cpovirk): It would be great to run all these tests (including class unloading) in an
   * environment that forces Futures.getChecked to its fallback WeakSetValidator. One awful way of
   * doing so would be to derive a separate test library by using remove_from_jar to strip out
   * ClassValueValidator.
   *

 * such custom interfaces directly; they are implemented only in subclasses. Therefore, forwarding
 * {@code equals} would break symmetry, as the forwarding object might consider itself equal to the
 * object being tested, but the reverse could not be true. This behavior is consistent with the
 * JDK's collection wrappers, such as {@link java.util.Collections#unmodifiableCollection}. Use an

It might also help avoid confusion for new developers that see an unused parameter in your code and could think it's unnecessary.

///

/// info

In this example we use invented custom headers `X-Key` and `X-Token`.

But in real cases, when implementing security, you would get more benefits from using the integrated [Security utilities (the next chapter)](../security/index.md){.internal-link target=_blank}.

        // This would integrate with SMB3 encryption/signing
        if (!isAuthorizedAccess(remoteAddress, length, remoteKey)) {
            throw new SecurityException("Unauthorized RDMA remote access");
        }
    }
    
    private boolean isAuthorizedAccess(long address, int length, int key) {
        // Implementation would check against established security context

   * {@code stream} and their indices in the stream. For example,
   *
   * {@snippet :
   * mapWithIndex(
   *     Stream.of("a", "b", "c"),
   *     (e, index) -> index + ":" + e)
   * }
   *
   * <p>would return {@code Stream.of("0:a", "1:b", "2:c")}.
   *
   * <p>The resulting stream is <a
   * href="http://gee.cs.oswego.edu/dl/html/StreamParallelGuidance.html">efficiently splittable</a>

        assertTrue(pacCredentialType.isCredentialTypeCorrect());
    }

    /**
     * Tests the isCredentialTypeCorrect method with a null byte array.
     * This test is indirect as the constructor would throw an exception.
     * We can't instantiate the class with null, so we can't directly test this method's behavior with null.
     * However, the constructor logic `!isCredentialTypeCorrect()` covers this.

   *
   * <p>Historically, {@code Predicate} instances in this library have implemented this method to
   * recognize certain cases where distinct {@code Predicate} instances would in fact behave
   * identically. However, as code migrates to {@code java.util.function}, that behavior will
   * disappear. It is best not to depend on it.
   */
  @Override
  boolean equals(@Nullable Object obj);

# Header Parameter Models { #header-parameter-models }

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

    assertThat(orig.toString())
        .contains("Exception thrown from implementation: class java.lang.StackOverflowError");
  }

  // Regression test for a case where we would fail to execute listeners immediately on done futures
  // this would be observable from an afterDone callback
  public void testListenersExecuteImmediately_fromAfterDone() {
    AbstractFuture<String> f =
        new AbstractFuture<String>() {