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https://github.com/spray/spray-json
A lightweight, clean and simple JSON implementation in Scala
https://github.com/spray/spray-json
json json-parser json-serialization scala
Last synced: 24 days ago
JSON representation
A lightweight, clean and simple JSON implementation in Scala
- Host: GitHub
- URL: https://github.com/spray/spray-json
- Owner: spray
- License: apache-2.0
- Created: 2011-05-06T21:31:38.000Z (over 13 years ago)
- Default Branch: release/1.3.x
- Last Pushed: 2024-01-10T20:17:55.000Z (10 months ago)
- Last Synced: 2024-10-02T03:03:11.689Z (about 1 month ago)
- Topics: json, json-parser, json-serialization, scala
- Language: Scala
- Homepage:
- Size: 902 KB
- Stars: 973
- Watchers: 37
- Forks: 190
- Open Issues: 102
-
Metadata Files:
- Readme: README.markdown
- Changelog: CHANGELOG.md
- License: LICENSE
Awesome Lists containing this project
- awesome-json - spray-json - A lightweight, clean and simple implementation in Scala. (Libraries)
- awesome-scala - **spray-json** - json)  (Table of Contents / JSON)
README
_spray-json_ is a lightweight, clean and efficient [JSON] implementation in Scala.
It supports the following features:
* A simple immutable model of the JSON language elements
* An efficient JSON parser
* Choice of either compact or pretty JSON-to-string printing
* Type-class based (de)serialization of custom objects (no reflection, no intrusion)
* No external dependencies
_spray-json_ allows you to convert between
* String JSON documents
* JSON Abstract Syntax Trees (ASTs) with base type JsValue
* instances of arbitrary Scala types
as depicted in this diagram:
### Installation
_spray-json_ is available from maven central.
Latest release: [](https://maven-badges.herokuapp.com/maven-central/io.spray/spray-json_2.12)
If you use SBT you can include _spray-json_ in your project with
```scala
libraryDependencies += "io.spray" %% "spray-json" % "1.3.6"
```
### Usage
_spray-json_ is really easy to use.
Just bring all relevant elements in scope with
```scala
import spray.json._
import DefaultJsonProtocol._ // if you don't supply your own Protocol (see below)
```
and do one or more of the following:
1. Parse a JSON string into its Abstract Syntax Tree (AST) representation
```scala
val source = """{ "some": "JSON source" }"""
val jsonAst = source.parseJson // or JsonParser(source)
```
2. Print a JSON AST back to a String using either the `CompactPrinter` or the `PrettyPrinter`
```scala
val json = jsonAst.prettyPrint // or .compactPrint
```
3. Convert any Scala object to a JSON AST using the `toJson` extension method
```scala
val jsonAst = List(1, 2, 3).toJson
```
4. Convert a JSON AST to a Scala object with the `convertTo` method
```scala
val myObject = jsonAst.convertTo[MyObjectType]
```
In order to make steps 3 and 4 work for an object of type `T` you need to bring implicit values in scope that
provide `JsonFormat[T]` instances for `T` and all types used by `T` (directly or indirectly).
The way you normally do this is via a "JsonProtocol".
### JsonProtocol
_spray-json_ uses [SJSON]s Scala-idiomatic type-class-based approach to connect an existing type `T` with the logic how
to (de)serialize its instances to and from JSON. (In fact _spray-json_ even reuses some of [SJSON]s code, see the
'Credits' section below).
This approach has the advantage of not requiring any change (or even access) to `T`s source code. All (de)serialization
logic is attached 'from the outside'. There is no reflection involved, so the resulting conversions are fast. Scalas
excellent type inference reduces verbosity and boilerplate to a minimum, while the Scala compiler will make sure at
compile time that you provided all required (de)serialization logic.
In _spray-jsons_ terminology a 'JsonProtocol' is nothing but a bunch of implicit values of type `JsonFormat[T]`, whereby
each `JsonFormat[T]` contains the logic of how to convert instance of `T` to and from JSON. All `JsonFormat[T]`s of a
protocol need to be "mece" (mutually exclusive, collectively exhaustive), i.e. they are not allowed to overlap and
together need to span all types required by the application.
This may sound more complicated than it is.
_spray-json_ comes with a `DefaultJsonProtocol`, which already covers all of Scala's value types as well as the most
important reference and collection types. As long as your code uses nothing more than these you only need the
`DefaultJsonProtocol`. Here are the types already taken care of by the `DefaultJsonProtocol`:
* Byte, Short, Int, Long, Float, Double, Char, Unit, Boolean
* String, Symbol
* BigInt, BigDecimal
* Option, Either, Tuple1 - Tuple7
* List, Array
* immutable.{Map, Iterable, Seq, IndexedSeq, LinearSeq, Set, Vector}
* collection.{Iterable, Seq, IndexedSeq, LinearSeq, Set}
* JsValue
In most cases however you'll also want to convert types not covered by the `DefaultJsonProtocol`. In these cases you
need to provide `JsonFormat[T]`s for your custom types. This is not hard at all.
### Providing JsonFormats for Case Classes
If your custom type `T` is a case class then augmenting the `DefaultJsonProtocol` with a `JsonFormat[T]` is really easy:
```scala
case class Color(name: String, red: Int, green: Int, blue: Int)
object MyJsonProtocol extends DefaultJsonProtocol {
implicit val colorFormat = jsonFormat4(Color)
}
import MyJsonProtocol._
import spray.json._
val json = Color("CadetBlue", 95, 158, 160).toJson
val color = json.convertTo[Color]
```
The `jsonFormatX` methods reduce the boilerplate to a minimum, just pass the right one the companion object of your
case class and it will return a ready-to-use `JsonFormat` for your type (the right one is the one matching the number
of arguments to your case class constructor, e.g. if your case class has 13 fields you need to use the `jsonFormat13`
method). The `jsonFormatX` methods try to extract the field names of your case class before calling the more general
`jsonFormat` overloads, which let you specify the field name manually. So, if spray-json has trouble determining the
field names or if your JSON objects use member names that differ from the case class fields you can also use
`jsonFormat` directly.
There is one additional quirk: If you explicitly declare the companion object for your case class the notation above will
stop working. You'll have to explicitly refer to the companion objects `apply` method to fix this:
```scala
case class Color(name: String, red: Int, green: Int, blue: Int)
object Color
object MyJsonProtocol extends DefaultJsonProtocol {
implicit val colorFormat = jsonFormat4(Color.apply)
}
```
If your case class is generic in that it takes type parameters itself the `jsonFormat` methods can also help you.
However, there is a little more boilerplate required as you need to add context bounds for all type parameters
and explicitly refer to the case classes `apply` method as in this example:
```scala
case class NamedList[A](name: String, items: List[A])
object MyJsonProtocol extends DefaultJsonProtocol {
implicit def namedListFormat[A :JsonFormat] = jsonFormat2(NamedList.apply[A])
}
```
#### NullOptions
The `NullOptions` trait supplies an alternative rendering mode for optional case class members. Normally optional
members that are undefined (`None`) are not rendered at all. By mixing in this trait into your custom JsonProtocol you
can enforce the rendering of undefined members as `null`.
(Note that this only affect JSON writing, spray-json will always read missing optional members as well as `null`
optional members as `None`.)
### Providing JsonFormats for other Types
Of course you can also supply (de)serialization logic for types that aren't case classes.
Here is one way to do it:
```scala
class Color(val name: String, val red: Int, val green: Int, val blue: Int)
object MyJsonProtocol extends DefaultJsonProtocol {
implicit object ColorJsonFormat extends RootJsonFormat[Color] {
def write(c: Color) =
JsArray(JsString(c.name), JsNumber(c.red), JsNumber(c.green), JsNumber(c.blue))
def read(value: JsValue) = value match {
case JsArray(Vector(JsString(name), JsNumber(red), JsNumber(green), JsNumber(blue))) =>
new Color(name, red.toInt, green.toInt, blue.toInt)
case _ => deserializationError("Color expected")
}
}
}
import MyJsonProtocol._
val json = new Color("CadetBlue", 95, 158, 160).toJson
val color = json.convertTo[Color]
```
This serializes `Color` instances as a JSON array, which is compact but does not make the elements semantics explicit.
You need to know that the color components are ordered "red, green, blue".
Another way would be to serialize `Color`s as JSON objects:
```scala
object MyJsonProtocol extends DefaultJsonProtocol {
implicit object ColorJsonFormat extends RootJsonFormat[Color] {
def write(c: Color) = JsObject(
"name" -> JsString(c.name),
"red" -> JsNumber(c.red),
"green" -> JsNumber(c.green),
"blue" -> JsNumber(c.blue)
)
def read(value: JsValue) = {
value.asJsObject.getFields("name", "red", "green", "blue") match {
case Seq(JsString(name), JsNumber(red), JsNumber(green), JsNumber(blue)) =>
new Color(name, red.toInt, green.toInt, blue.toInt)
case _ => throw new DeserializationException("Color expected")
}
}
}
}
```
This is a bit more verbose in its definition and the resulting JSON but transports the field semantics over to the
JSON side. Note that this is the approach _spray-json_ uses for case classes.
### Providing JsonFormats for unboxed types
A value class
```scala
case class PhoneNumber(value: String) extends AnyVal
val num = PhoneNumber("+1 212 555 1111")
```
or a class with multiple members
```scala
case class Money(currency: String, amount: BigDecimal)
val bal = Money("USD", 100)
```
can be handled as above with `jsonFormatX`, etc.
It may be preferable, however, to serialize such instances without object boxing:
as `"USD 100"` instead of `{"currency":"USD","amount":100}`.
This requires explicit (de)serialization logic:
```scala
implicit object MoneyFormat extends JsonFormat[Money] {
val fmt = """([A-Z]{3}) ([0-9.]+)""".r
def write(m: Money) = JsString(s"${m.currency} ${m.amount}")
def read(json: JsValue) = json match {
case JsString(fmt(c, a)) => Money(c, BigDecimal(a))
case _ => deserializationError("String expected")
}
}
```
### JsonFormat vs. RootJsonFormat
According to the JSON specification not all of the defined JSON value types are allowed at the root level of a JSON
document. A JSON string for example (like `"foo"`) does not constitute a legal JSON document by itself.
Only JSON objects or JSON arrays are allowed as JSON document roots.
In order to distinguish, on the type-level, "regular" JsonFormats from the ones producing root-level JSON objects or
arrays _spray-json_ defines the [`RootJsonFormat`][1] type, which is nothing but a marker specialization of `JsonFormat`.
Libraries supporting _spray-json_ as a means of document serialization might choose to depend on a `RootJsonFormat[T]`
for a custom type `T` (rather than a "plain" `JsonFormat[T]`), so as to not allow the rendering of illegal document
roots. E.g., the `SprayJsonSupport` trait of _spray-routing_ is one notable example of such a case.
All default converters in the `DefaultJsonProtocol` producing JSON objects or arrays are actually implemented as
`RootJsonFormat`. When "manually" implementing a `JsonFormat` for a custom type `T` (rather than relying on case class
support) you should think about whether you'd like to use instances of `T` as JSON document roots and choose between
a "plain" `JsonFormat` and a `RootJsonFormat` accordingly.
[1]: http://spray.github.com/spray/api/spray-json/cc/spray/json/RootJsonFormat.html
### JsonFormats for recursive Types
If your type is recursive such as
```scala
case class Foo(i: Int, foo: Foo)
```
you need to wrap your format constructor with `lazyFormat` and supply an explicit type annotation:
```scala
implicit val fooFormat: JsonFormat[Foo] = lazyFormat(jsonFormat(Foo, "i", "foo"))
```
Otherwise your code will either not compile (no explicit type annotation) or throw an NPE at runtime (no `lazyFormat`
wrapper). Note, that `lazyFormat` returns a `JsonFormat` even if it was given a `RootJsonFormat` which means it isn't
picked up by `SprayJsonSupport`. To get back a `RootJsonFormat` just wrap the complete `lazyFormat` call with another
call to `rootFormat`.
### Customizing Parser Settings
The parser can be customized by providing a custom instance of `JsonParserSettings` to `JsonParser.apply` or
`String.parseJson`:
```scala
val customSettings =
JsonParserSettings.default
.withMaxDepth(100)
.withMaxNumberCharacters(20)
val jsValue = JsonParser(jsonString, customSettings)
// or
val jsValue = jsonString.parseJson(customSettings)
```
### Credits
Most of type-class (de)serialization code is nothing but a polished copy of what **Debasish Ghosh** made available
with his [SJSON] library. These code parts therefore bear his copyright.
Additionally the JSON AST model is heavily inspired by the one contributed by **Jorge Ortiz** to [Databinder-Dispatch].
### License
_spray-json_ is licensed under [APL 2.0].
### Mailing list
Spray-json is in primarily "maintanance mode", as it contains the basic functionality it is meant to deliver.
If you have any questions about it though, please open issues on this repository.
### Maintanance mode
_spray-json_ is largely considered feature-complete for the basic functionality it provides.
It is currently maintained by the Akka team at Lightbend.
Feedback and contributions to the project, no matter what kind, are always very welcome.
Along with any patches, please state that the patch is your original work and that you license the work to the
_spray-json_ project under the project’s open source license.
[JSON]: http://json.org
[SJSON]: https://github.com/debasishg/sjson
[Databinder-Dispatch]: https://github.com/dispatch/classic
[APL 2.0]: http://www.apache.org/licenses/LICENSE-2.0