PHP-Jackson

A lightweight, flexible object serializer for PHP, inspired by Jackson.

It provides strong typing, JSON ↔ object mapping, generics support, array/object shapes, custom type mappers, and detailed error tracing.

📚 Contents

• Overview
• Integrations
  • Laravel ↗
  • Symfony ↗
  • Guzzle ↗
• Installation
• Basic Usage
• Deserializing from JSON
• Merging Additional Data (readValueWith)
• Serializing Objects
• Generic Types (list<t> map<k, v> shapes)
  • List Example
  • Map Example
  • Array Shape Example
  • Object Shape Example
• Renaming JSON keys with #[JsonProperty]
• Custom Type Mappers
  • Using Custom Mappers with External Context
  • Pinning a Mapper on the Class with #[JsonMapper]
• Date Handling
• Error Handling
• Development
• Summary

---

Overview

Main components:

• JsonObjectMapper — handles JSON strings at the boundary.
• ArrayObjectMapper — handles associative arrays at the boundary.
• Type Mappers — custom readers/writers for specific classes.
• Generic Types — support for list<T>, map<K,V>, shapes, etc.
• Date Handling — built-in support for DateTime and Carbon.
• Error Reporting — typed exceptions with full trace paths.

---

🚀 Installation

composer require tcds-io/php-jackson

🧩 Integrations

PHP Jackson offers first-class integrations for popular PHP frameworks and tools. Each integration extends the core mapper with framework-specific features for a smoother development experience.

Official Plugins:

• Laravel ↗ — controller injection, JSON responses, request error handling, and Eloquent casts
• Symfony ↗ — controller argument resolvers, JSON responses, and configurable request error handling
• Guzzle ↗ — typed HTTP client with request DTO mapping and async response parsing

🔧 Basic Usage

Reading JSON into typed objects

use Tcds\Io\Jackson\JsonObjectMapper;

$mapper = new JsonObjectMapper();

$address = $mapper->readValue(Address::class, $json);

Equivalent array version:

use Tcds\Io\Jackson\ArrayObjectMapper;

$mapper = new ArrayObjectMapper();

$address = $mapper->readValue(Address::class, $dataArray);

---

📥 Deserializing from JSON

$json = <<<JSON
{
    "street": "Ocean avenue",
    "number": "100",
    "main": "true",
    "place": {
        "city": "Rio de Janeiro",
        "country": "Brazil",
        "position": { "lat": "-26.9013", "lng": "-48.6655" }
    }
}
JSON;

$mapper = new JsonObjectMapper();

$address = $mapper->readValue(Address::class, $json);

The resulting object matches:

new Address(
    street: 'Ocean avenue',
    number: 100,
    main: true,
    place: new Place(
        city: 'Rio de Janeiro',
        country: 'Brazil',
        position: new LatLng(lat: -26.9013, lng: -48.6655),
    ),
);

---

➕ Merging Additional Data (readValueWith)

Merging data is useful when the incoming payload does not contain all required values and those values must be completed from another source:

$partial = <<<JSON
{
    "street": "Ocean avenue",
    "number": "100",
    "main": "true"
}
JSON;

$address = $mapper->readValueWith(
    Address::class,
    $partial,
    [
        'place' => [
            'city' => "Rio de Janeiro",
            'country' => "Brazil",
            'position' => [
                'lat' => -26.9013,
                'lng' => -48.6655,
            ]
        ]
    ]
);

---

📤 Serializing Objects

Array output:

$mapper = new ArrayObjectMapper();
$array = $mapper->writeValue($object);

JSON output:

$mapper = new JsonObjectMapper();
$json = $mapper->writeValue($object);

---

📚 Generic Types (list<T>, map<K,V>, shapes)

The generic() and shape() helper functions are loaded by Composer through php-better-generics.

List example

$list = $mapper->readValue('list<LatLng>', $json);

Using generic():

$type = generic('list', [LatLng::class]);

$list = $mapper->readValue($type, $json);

---

Map example

$type = generic('map', ['string', Address::class]);

$result = $mapper->readValue($type, [
    'main'  => Address::mainData(),
    'other' => Address::otherData(),
]);

---

Array Shape Example

$type = shape('array', [
    'type'     => AccountType::class,
    'position' => LatLng::class,
]);

Produces:

[
  'type' => AccountType::CHECKING,
  'position' => new LatLng(...),
]

---

Object Shape Example

$type = shape('object', [
    'type'     => AccountType::class,
    'position' => LatLng::class
]);

Produces a stdClass:

$object->type     === AccountType::CHECKING
$object->position instanceof LatLng

---

🏷️ Renaming JSON keys with #[JsonProperty]

PHP-Jackson maps JSON keys to PHP names 1:1 by default. When the wire format uses a different naming convention (snake_case, kebab-case, etc.), pin the JSON key on the constructor parameter (or property) with #[JsonProperty]:

use Tcds\Io\Jackson\Node\JsonProperty;

readonly class User
{
    public function __construct(
        #[JsonProperty('first_name')] public string $firstName,
        #[JsonProperty('last_name')] public string $lastName,
        public int $age,
    ) {}
}

The attribute is honored on both directions:

$mapper = new JsonObjectMapper();

$user = $mapper->readValue(User::class, '{"first_name":"Arthur","last_name":"Dent","age":42}');
// User { firstName: "Arthur", lastName: "Dent", age: 42 }

$mapper->writeValue($user);
// {"first_name":"Arthur","last_name":"Dent","age":42}

Error traces and the expected payload on UnableToParseValue use the wire key — the one users will recognize from the JSON they are sending — not the PHP identifier.

---

🧩 Custom Type Mappers

Custom mappers are useful when object construction depends on complex logic or external data:

use Tcds\Io\Jackson\ArrayObjectMapper;

$mapper = new ArrayObjectMapper(
    typeMappers: [
        LatLng::class => [
            'reader' => fn(string $data) => new LatLng(...explode(',', $data)),
            'writer' => fn(LatLng $data) => sprintf("%s, %s", $data->lat, $data->lng),
        ]
    ]
);

This allows:

"position" => "-26.9013, -48.6655"

to become:

new LatLng(-26.9013, -48.6655)

and serialize back into:

"position" => "-26.9013, -48.6655"

---

Using Custom Mappers with External Context

use Tcds\Io\Jackson\ArrayObjectMapper;

$mapper = new ArrayObjectMapper(
    typeMappers: [
        User::class => [
            'reader' => fn() => Auth::user(),
            'writer' => fn(User $data) => [
                'id' => $data->id,
                'name' => $data->name,
                // 'email' intentionally omitted
            ],
        ]
    ]
);

Mapper closures can receive any of the named arguments used internally by PHP-Jackson:

fn(mixed $data, string $type, ObjectMapper $mapper, array $path): mixed

Use only the parameters you need; ReflectionFunction::call() binds them by name.

---

Pinning a Mapper on the Class with #[JsonMapper]

If a class always wants the same custom (de)serialization, declare it once on the class itself instead of registering it on every mapper instance:

use Tcds\Io\Jackson\Node\JsonMapper;

#[JsonMapper(reader: MoneyReader::class, writer: MoneyWriter::class)]
readonly class Money
{
    public function __construct(public int $cents) {}
}

The reader and writer accept any of:

• a class string of an implementation of Reader / Writer (instance is built with a no-arg constructor),
• a class string of StaticReader / StaticWriter (no instance — the static read / write is called),
• a class string of any class with a matching __invoke (treated as a MapperClosure),
• an instance of Reader / Writer (PHP 8.1 new in attribute initializers),
• a Closure matching MapperClosure, when constructing JsonMapper programmatically (PHP attribute literals can't carry closures).

Resolution order on every read/write:

1. #[JsonMapper] attribute on the target class — declaration site, wins
2. typeMappers constructor argument
3. default reader/writer

That is, an explicit class-level mapper cannot be silently overridden by mapper-instance config — the class itself is the canonical source.

---

🕒 Date Handling

PHP-Jackson provides built-in support for:

• DateTime
• DateTimeImmutable
• Carbon
• CarbonImmutable
• DateTimeInterface

Dates are serialized and deserialized using ISO-8601 strings:

[
  'datetime' => '2025-10-22T11:21:31+00:00'
]

---

❗ Error Handling

When parsing fails, the library throws:

UnableToParseValue

Properties:

$e->trace;     // ['address','place','position']
$e->expected;  // expected type description
$e->given;     // actual given value

Example message:

Unable to parse value at .address.place.position

This makes debugging extremely easy.

---

🔧 Development

composer install
composer tests       # runs cs:check + phpstan + phpunit
composer cs:fix      # auto-fix code style

---

✅ Summary

You can:

• Read JSON → typed objects via JsonObjectMapper
• Read arrays → typed objects via ArrayObjectMapper
• Merge missing fields using readValueWith
• Write objects → JSON/arrays via writeValue
• Use generics (list<T>, map<K,V>, shapes)
• Rename wire keys per field with #[JsonProperty('snake_case')]
• Register custom mappers for any class via typeMappers or pin them on the class itself with #[JsonMapper(reader: …, writer: …)]
• Rely on strong error tracing with full path information