## An app with callbacks { #an-app-with-callbacks }

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

			// then it is implicit on for the sub-system.
			enabled = true
		}
		v, _ := currKVS.Lookup(hkv.Key)
		if v == "" && !hkv.Optional && enabled {
			// Return error only if the
			// key is enabled, for state=off
			// let it be empty.
			return false, Errorf(
				"'%s' is not optional for '%s' sub-system, please check '%s' documentation",
				hkv.Key, subSys, subSys)
		}
	}
	c[subSys][tgt] = currKVS

 * to add or remove multiple occurrences of an element at once, or to set the count of an element to
 * a specific value. These modification operations are optional, but implementations which support
 * the standard collection operations {@link #add(Object)} or {@link #remove(Object)} are encouraged
 * to implement the related methods as well. Finally, two collection views are provided: {@link

    * **WebSockets**
    * HTTPX ve `pytest` tabanlı aşırı kolay testler
    * **CORS**
    * **Cookie Sessions**
    * ...ve daha fazlası.

### Uygulamanızı deploy edin (opsiyonel) { #deploy-your-app-optional }

İsterseniz FastAPI uygulamanızı [FastAPI Cloud](https://fastapicloud.com)'a deploy edebilirsiniz; eğer henüz yapmadıysanız gidip bekleme listesine katılın. 🚀

Shared scheme

```
org.gradle[.<qualifier>].<feature-name>.<detail>
```

The optional qualifier defines the secondary aspects, if any.

For better ergonomics on the CLI, some properties can have supplementary command-line build option(s).

import org.codelibs.fess.dict.synonym.SynonymItem;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.ActionResponse;
import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;

* (Starlette 덕분에) 많은 추가 기능:
    * **웹 소켓**
    * HTTPX 및 `pytest`에 기반한 극히 쉬운 테스트
    * **CORS**
    * **쿠키 세션**
    * ...기타 등등.

### 앱 배포하기(선택 사항) { #deploy-your-app-optional }

선택적으로 FastAPI 앱을 [FastAPI Cloud](https://fastapicloud.com)에 배포할 수 있습니다. 아직이라면 대기자 명단에 등록해 보세요. 🚀

이미 **FastAPI Cloud** 계정이 있다면(대기자 명단에서 초대해 드렸습니다 😉), 한 번의 명령으로 애플리케이션을 배포할 수 있습니다.

<div class="termy">

import org.codelibs.fess.query.QueryFieldConfig;
import org.codelibs.fess.query.parser.QueryParser;
import org.codelibs.fess.score.QueryRescorer;
import org.codelibs.fess.util.ComponentUtil;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.core.message.UserMessages;
import org.lastaflute.web.util.LaRequestUtil;
import org.opensearch.action.search.SearchRequestBuilder;
import org.opensearch.index.query.BoolQueryBuilder;

To get a connection to a specific server, use `Manager.Connection(host)` to get a connection to the specified host.
From this connection individual requests can be made.

Each handler, with optional subroutes can be registered with the manager using
`Manager.RegisterXHandler(handlerID, handler, subroutes...)`.

A `Handler()` function provides an HTTP handler, which should be hooked up to the appropriate route on the server.

import org.jspecify.annotations.Nullable;

/**
 * CompactLinkedHashMap is an implementation of a Map with insertion or LRU iteration order,
 * maintained with a doubly linked list through the entries. All optional operations (put and
 * remove) are supported. Null keys and values are supported.
 *
 * <p>{@code containsKey(k)}, {@code put(k, v)} and {@code remove(k)} are all (expected and