/*
         * It's very unlikely that any loaded Futures class will see getChecked called with more
         * than a handful of exceptions. But it seems prudent to set a cap on how many we'll cache.
         * This avoids out-of-control memory consumption, and it keeps the cache from growing so
         * large that doing the lookup is noticeably slower than redoing the work would be.
         *

Events
======

Events allow you to capture metrics on your application’s HTTP calls. Use events to monitor:

 * The size and frequency of the HTTP calls your application makes. If you’re making too many calls, or your calls are too large, you should know about it!
 * The performance of these calls on the underlying network. If the network’s performance isn’t sufficient, you need to either improve the network or use less of it.

### EventListener

        Set<ConstraintViolation<TestBean>> violations = validator.validate(bean);
        assertFalse(violations.isEmpty());
        assertEquals(1, violations.size());

        // Test too many fields
        bean.setCronExpression("* * * * * * * *");
        violations = validator.validate(bean);
        assertFalse(violations.isEmpty());

        // Test too few fields

        /*
         * It's very unlikely that any loaded Futures class will see getChecked called with more
         * than a handful of exceptions. But it seems prudent to set a cap on how many we'll cache.
         * This avoids out-of-control memory consumption, and it keeps the cache from growing so
         * large that doing the lookup is noticeably slower than redoing the work would be.
         *

Public License.  It also provides other free software developers Less
of an advantage over competing non-free programs.  These disadvantages
are the reason we use the ordinary General Public License for many
libraries.  However, the Lesser license provides advantages in certain
special circumstances.

  For example, on rare occasions, there may be a special need to

        assertNull(emptyIterator.next(), "Final next call");
    }

    @Test
    @DisplayName("EmptyIterator should be lightweight and efficient")
    void testPerformanceCharacteristics() {
        // When - create many instances quickly
        long startTime = System.currentTimeMillis();

        for (int i = 0; i < 10000; i++) {
            EmptyIterator iterator = new EmptyIterator();
            iterator.hasNext();

    expected.addAll(index, elements);
    expectContents(expected);
  }

  /*
   * TODO: if we're testing a list, we could check indexOf(). (Doing it in
   * AbstractListTester isn't enough because many tests that run on lists don't
   * extends AbstractListTester.) We could also iterate over all elements to
   * verify absence
   */
  protected void expectMissing(E... elements) {
    for (E element : elements) {

<img src="/img/tutorial/additional-responses/image01.png">

## Combine predefined responses and custom ones { #combine-predefined-responses-and-custom-ones }

You might want to have some predefined responses that apply to many *path operations*, but you want to combine them with custom responses needed by each *path operation*.

For those cases, you can use the Python technique of "unpacking" a `dict` with `**dict_to_unpack`:

```Python

# Behind a Proxy { #behind-a-proxy }

In many situations, you would use a **proxy** like Traefik or Nginx in front of your FastAPI app.

These proxies could handle HTTPS certificates and other things.

## Proxy Forwarded Headers { #proxy-forwarded-headers }

## Pydantic

Toda la validación de datos se realiza internamente con <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a>, así que obtienes todos los beneficios de esta. Y sabes que estás en buenas manos.

Puedes usar las mismas declaraciones de tipo con `str`, `float`, `bool` y muchos otros tipos de datos complejos.

Varios de estos se exploran en los siguientes capítulos del tutorial.

## El orden importa