## 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):

 * When making TLS connections with multiple [connection specs](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-connection-spec/), these are attempted in sequence until the TLS handshake succeeds.

### [Connections](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-connection/)

When you request a URL with OkHttp, here's what it does:

//
// Scanning stops if the function returns an error, in which case some of
// the input may be discarded. If that error is [ErrFinalToken], scanning
// stops with no error. A non-nil token delivered with [ErrFinalToken]
// will be the last token, and a nil token with [ErrFinalToken]
// immediately stops the scanning.
//
// Otherwise, the [Scanner] advances the input. If the token is not nil,

///

/// tip

Notice how each model's attribute with a type, default value and `Field` has the same structure as a *path operation function's* parameter, with `Field` instead of `Path`, `Query` and `Body`.

///

## Add extra information { #add-extra-information }

        assertEquals(0, dst[35]);
    }

    @Test
    @DisplayName("Test writeParameterWordsWireFormat with zero parameter count")
    void testWriteParameterWordsWireFormatZeroParameters() {
        byte[] dst = new byte[256];

        // Set up transaction with zero parameters
        transaction.setTotalParameterCount(0);
        transaction.setTotalDataCount(100);

        assertSame(tz1, tz2);
        assertSame(FessUserTimeZoneProcessProvider.centralTimeZone, tz1);
    }

    // Test with null RequestManager (edge case)
    public void test_getRequestedTimeZone_withNullRequestManager() {
        // Execute with null request manager
        TimeZone result = provider.getRequestedTimeZone(null);

        // Should still return the central time zone

            assertNotNull(buffer.getReferrals());
            assertEquals(0, buffer.getReferrals().length);
        }

        @Test
        @DisplayName("Should decode buffer with single referral")
        void testDecodeSingleReferral() {
            // Create buffer with one v3 referral
            byte[] testBuffer = new byte[100];
            ByteBuffer bb = ByteBuffer.wrap(testBuffer).order(ByteOrder.LITTLE_ENDIAN);

 * including retrieval, storage, deletion, and search functionality.
 * It handles pagination and integrates with the file authentication system.
 */
public class FileConfigService extends FessAppService {

    /**
     * Default constructor for file configuration service.
     * Creates a new instance with default values.
     */
    public FileConfigService() {
        super();
    }

    /**

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

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