///

## Override the default exception handlers { #override-the-default-exception-handlers }

**FastAPI** has some default exception handlers.

These handlers are in charge of returning the default JSON responses when you `raise` an `HTTPException` and when the request has invalid data.

You can override these exception handlers with your own.

{* ../../docs_src/events/tutorial001_py310.py hl[8] *}

In this case, the `startup` event handler function will initialize the items "database" (just a `dict`) with some values.

You can add more than one event handler function.

And your application won't start receiving requests until all the `startup` event handlers have completed.

### `shutdown` event { #shutdown-event }

        assert client.app_state == {"router": True}


@pytest.mark.filterwarnings(
    r"ignore:\s*on_event is deprecated, use lifespan event handlers instead.*:DeprecationWarning"
)
def test_router_async_shutdown_handler(state: State) -> None:
    """Test that async on_shutdown event handlers are called correctly, for coverage."""
    app = FastAPI()

    @app.get("/")
    def main() -> dict[str, str]:

        }
    }

    /**
     * Loads protocol handlers from the specified base package by scanning for
     * Handler classes in subpackages and registering them as web or file protocols
     * based on their PROTOCOL_TYPE field.
     *
     * @param basePackage the base package to scan for protocol handlers
     */
    protected void loadProtocols(final String basePackage) {

This was changed in version 0.110.0 to fix unhandled memory consumption from forwarded exceptions without a handler (internal server errors), and to make it consistent with the behavior of regular Python code.

            filterPanel: $('#filterPanel')
        };

        bindEvents();
        autoResizeTextarea();
        updateCharCount();
        showStatus('ready');
    }

    /**
     * Bind event handlers
     */
    function bindEvents() {
        elements.sendBtn.on('click', sendMessage);

        elements.chatInput.on('keydown', function(e) {

new_app = UnicornMiddleware(app, some_config="rainbow")
```

But FastAPI (actually Starlette) provides a simpler way to do it that makes sure that the internal middlewares handle server errors and custom exception handlers work properly.

For that, you use `app.add_middleware()` (as in the example for CORS).

```Python
from fastapi import FastAPI
from unicorn import UnicornMiddleware

app = FastAPI()

    /**
     * Dispatches an event to all registered handlers for the event name.
     *
     * @param event the event to dispatch.
     */
    protected void dispatchEvent(final EventInfo event) {
        final List<Consumer<EventInfo>> handlers = eventHandlers.get(event.name);
        if (handlers != null) {
            for (final Consumer<EventInfo> handler : handlers) {
                try {

おそらくコードの中で直接使用する必要はないでしょう。

しかし、高度なシナリオのために必要な場合には、カスタムヘッダーを追加することができます:

{* ../../docs_src/handling_errors/tutorial002_py310.py hl[14] *}

## カスタム例外ハンドラのインストール { #install-custom-exception-handlers }

カスタム例外ハンドラは[Starletteと同じ例外ユーティリティ](https://www.starlette.dev/exceptions/)を使用して追加することができます。

あなた（または使用しているライブラリ）が`raise`するかもしれないカスタム例外`UnicornException`があるとしましょう。

そして、この例外をFastAPIでグローバルに処理したいと思います。

│   │   ├── admin/             # Admin controllers ({feature}/ with Action, Forms)
│   │   └── api/               # API controllers
│   ├── service/               # Business logic services
│   ├── pager/                 # Pagination handlers
│   └── job/                   # Background jobs
├── api/                       # REST API infrastructure
├── opensearch/                # DBFlute integration for OpenSearch