## 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):

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.codelibs.fess.opensearch.config.exentity.LabelType;
import org.codelibs.fess.util.ComponentUtil;
import org.dbflute.bhv.readable.EntityRowHandler;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.optional.OptionalEntity;

import com.orangesignal.csv.CsvConfig;
import com.orangesignal.csv.CsvReader;
import com.orangesignal.csv.CsvWriter;

import jakarta.annotation.Resource;

/**

    /** ISO datetime format pattern with milliseconds and UTC timezone. */
    public static final String ISO_DATETIME_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'";

    /** Date optional time format identifier. */
    public static final String DATE_OPTIONAL_TIME = "date_optional_time";

    // ============================================================
    // Default Values and Status

import java.util.NavigableMap;
import java.util.NoSuchElementException;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * An implementation of {@code RangeMap} based on a {@code TreeMap}, supporting all optional
 * operations.
 *
 * <p>Like all {@code RangeMap} implementations, this supports neither null keys nor null values.
 *
 * @author Louis Wasserman
 * @since 14.0
 */

    - [DELETE operation in REST API](#delete-operation-in-rest-api)
  - [Action Required Before Upgrading](#action-required-before-upgrading)
- [optionally, remove the old secret](#optionally-remove-the-old-secret)
  - [Previous Releases Included in v1.4.0](#previous-releases-included-in-v140)
- [v1.4.0-beta.11](#v140-beta11)
  - [Downloads](#downloads-6)

### Technical details about the JWT "subject" `sub` { #technical-details-about-the-jwt-subject-sub }

The JWT specification says that there's a key `sub`, with the subject of the token.

It's optional to use it, but that's where you would put the user's identification, so we are using it here.

JWT might be used for other things apart from identifying a user and allowing them to perform operations directly on your API.

Вы также можете использовать её для автоматической генерации кода для клиентов, которые взаимодействуют с вашим API. Например, для фронтенд-, мобильных или IoT-приложений.

### Разверните приложение (необязательно) { #deploy-your-app-optional }

При желании вы можете развернуть своё приложение FastAPI в <a href="https://fastapicloud.com" class="external-link" target="_blank">FastAPI Cloud</a>, перейдите и присоединитесь к списку ожидания, если ещё не сделали этого. 🚀

import org.codelibs.spnego.SpnegoHttpFilter;
import org.codelibs.spnego.SpnegoHttpFilter.Constants;
import org.codelibs.spnego.SpnegoHttpServletResponse;
import org.codelibs.spnego.SpnegoPrincipal;
import org.dbflute.optional.OptionalEntity;
import org.lastaflute.web.login.credential.LoginCredential;
import org.lastaflute.web.response.ActionResponse;
import org.lastaflute.web.servlet.filter.RequestLoggingFilter;

 * {@linkplain Comparable natural ordering} also does not permit insertion of non-comparable objects
 * (doing so results in {@code ClassCastException}).
 *
 * <p>This class and its iterator implement all of the optional methods of the {@link
 * Collection} and {@link Iterator} interfaces. The Iterator provided in method {@link #iterator()}
 * is not guaranteed to traverse the elements of the MonitorBasedPriorityBlockingQueue in