Actually, `Query`, `Path` and others you'll see next create objects of subclasses of a common `Param` class, which is itself a subclass of Pydantic's `FieldInfo` class.

And Pydantic's `Field` returns an instance of `FieldInfo` as well.

`Body` also returns objects of a subclass of `FieldInfo` directly. And there are others you will see later that are subclasses of the `Body` class.

  public void testSubtypeOfInnerClass_nonStaticAnonymousClass() {
    TypeToken<?> supertype = new TypeToken<Mall<Outdoor>.Shop<Electronics>>() {};
    Class<?> subclass = new Mall<Outdoor>().new Shop<Electronics>() {}.getClass();
    assertTrue(TypeToken.of(subclass).isSubtypeOf(supertype));
  }

  @SuppressWarnings("RestrictedApiChecker") // crashes under JDK8, which EP no longer supports

* Decompressing gzip-compressed request bodies.
* Automatically logging all request bodies.

## Handling custom request body encodings

Let's see how to make use of a custom `Request` subclass to decompress gzip requests.

And an `APIRoute` subclass to use that custom request class.

### Create a custom `GzipRequest` class

/// tip

        // The raw class isn't even a subclass.
      }
    }
    if (!spec.suppressGetSupertype()) {
      try {
        assertThat(getSupertype(paramType, TypeToken.of(returnType).getRawType()))
            .isNotEqualTo(returnType);
      } catch (IllegalArgumentException notSubtype2) {
        // The raw class isn't even a subclass.
      }
    }
    return null;
  }

/**
 * Tests that all package-private {@code writeReplace} methods are overridden in any existing
 * subclasses. Without such overrides, optimizers might put a {@code writeReplace}-containing class
 * and its subclass in different packages, causing the serialization system to fail to invoke {@code
 * writeReplace} when serializing an instance of the subclass. For an example of this problem, see
 * b/310253115.
 */

        // The raw class isn't even a subclass.
      }
    }
    if (!spec.suppressGetSupertype()) {
      try {
        assertThat(getSupertype(paramType, TypeToken.of(returnType).getRawType()))
            .isNotEqualTo(returnType);
      } catch (IllegalArgumentException notSubtype2) {
        // The raw class isn't even a subclass.
      }
    }
    return null;
  }

 *
 * <p>For details about this hack, see {@code GwtSerializationDependencies}, which takes the same
 * approach but with a subclass rather than a superclass.
 *
 * <p>TODO(cpovirk): Consider applying this subclass approach to our other types.
 */
@SuppressWarnings("rawtypes") // https://github.com/google/guava/issues/989
@GwtCompatible(emulated = true)

import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;

/**
 * Verifies that subclasses from generated model classes are possible.
 */
class ExtendedPluginDescriptorTest {

    /**
     * A subclass of the generated class {@link PluginDescriptor} that adds an additional field.
     */
    public static class ExtendedPluginDescriptor extends PluginDescriptor {

This simple case is handled automatically by FastAPI because the return type annotation is the class (or a subclass of) `Response`.

And tools will also be happy because both `RedirectResponse` and `JSONResponse` are subclasses of `Response`, so the type annotation is correct.

### Annotate a Response Subclass

You can also use a subclass of `Response` in the type annotation:

```Python hl_lines="8-9"

   * {@link ForwardingMap#entrySet}. In many cases, you may wish to override {@link
   * ForwardingMap#keySet} to forward to this implementation or a subclass thereof.
   *
   * @since 10.0
   */
  protected class StandardKeySet extends Maps.KeySet<K, V> {
    /** Constructor for use by subclasses. */
    public StandardKeySet() {
      super(ForwardingMap.this);
    }
  }

  /**