中间件不必是专为 FastAPI 或 Starlette 定制的，只要遵循 ASGI 规范即可。

总之，ASGI 中间件是类，并把 ASGI 应用作为第一个参数。

因此，有些第三方 ASGI 中间件的文档推荐以如下方式使用中间件：

```Python
from unicorn import UnicornMiddleware

app = SomeASGIApp()

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

但 FastAPI（实际上是 Starlette）提供了一种更简单的方式，能让内部中间件在处理服务器错误的同时，还能让自定义异常处理器正常运作。

为此，要使用 `app.add_middleware()` （与 CORS 中的示例一样）。

```Python
from fastapi import FastAPI

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
public class MapSizeTester<K, V> extends AbstractMapTester<K, V> {
  public void testSize() {
    assertEquals("size():", getNumElements(), getMap().size());
  }

    app.include_router(router)
    app.include_router(prefix_router, prefix="/prefix")
    app.include_router(native_prefix_route)
    return app


app = make_app(app)


def test_app():
    client = TestClient(app)
    with client.websocket_connect("/") as websocket:
        data = websocket.receive_text()
        assert data == "Hello, world!"


def test_router():

    protected void testRead() {
        final Map<String, Object> searchBody = new HashMap<>();
        String response = checkGetMethod(searchBody, "").asString();
        final Map<String, Object> res = JsonPath.from(response).getMap("response");
        assertTrue(res.containsKey("env_props"));
        assertTrue(res.containsKey("system_props"));
        assertTrue(res.containsKey("fess_props"));
        assertTrue(res.containsKey("bug_report_props"));

    protected void testRead() {
        final Map<String, Object> searchBody = new HashMap<>();
        String response = checkGetMethod(searchBody, "").asString();
        final Map<String, Object> res = JsonPath.from(response).getMap("response.setting");
        assertTrue(!res.isEmpty());
        assertEquals(new Integer(0), JsonPath.from(response).get("response.status"));
    }

    @Override
    protected void tearDown() {
        // do nothing

So, in the documentation for third-party ASGI middlewares they will probably tell you to do something like:

```Python
from unicorn import UnicornMiddleware

app = SomeASGIApp()

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.

    assertEquals("get(null) should return the associated value", getValueForNullKey(), get(null));
  }

  public void testGet_wrongType() {
    try {
      assertNull("get(wrongType) should return null or throw", getMap().get(WrongType.VALUE));
    } catch (ClassCastException tolerated) {
    }
  }

In der Dokumentation für ASGI-Middlewares von Drittanbietern wird Ihnen wahrscheinlich gesagt, etwa Folgendes zu tun:

```Python
from unicorn import UnicornMiddleware

app = SomeASGIApp()

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

class APIRouteC(APIRoute):
    x_type = "C"


router_a = APIRouter(route_class=APIRouteA)
router_b = APIRouter(route_class=APIRouteB)
router_c = APIRouter(route_class=APIRouteC)


@router_a.get("/")
def get_a():
    return {"msg": "A"}


@router_b.get("/")
def get_b():
    return {"msg": "B"}


@router_c.get("/")
def get_c():
    return {"msg": "C"}

  private SortedMap<K, V> navigableMap;
  private Entry<K, V> a;
  private Entry<K, V> c;

  @Override
  public void setUp() throws Exception {
    super.setUp();
    navigableMap = (SortedMap<K, V>) getMap();
    List<Entry<K, V>> entries =
        copyToList(
            getSubjectGenerator()
                .getSampleElements(getSubjectGenerator().getCollectionSize().getNumElements()));