Krypton

A straight-forward Java model of JSON schemas (Draft 4).

Krypton allows developers to work with JSON schemas using Java.

Get Started

Krypton requires Java 7 or later.

Get from Maven Central...

<dependency>
  <groupId>com.github.hgwood.nobleschemas</groupId>
  <artifactId>krypton</artifactId>
  <version>1.1.0</version>
</dependency>

group: 'com.github.hgwood.nobleschemas', name: 'krypton', version: '1.1.0'

...or build from sources

mvn install

Usage

Use Jackson Databind's ObjectMapper to read the serialized JSON schema into Krypton's Schema class.

try (InputStream schemaStream = getClass().getResourceAsStream("schema.json")) {
    return new ObjectMapper().readValue(schemaStream, Schema.class);
}

Krypton requires Jackson 2.7 or later. Serialization is also supported.

Specification Support

Krypton is able to deserialize all fields of all objects defined in the JSON Schema Draft 4 specification, without known limitation. Please open an issue if you detect any.

Please note however, that there is no validation aside from basic type correctness. For example, Krypton does not verify that values in the required property are actually the names of properties, only that they are strings.

Technical choices

The objects defined by the spec are modeled in a simple way, without resorting to inheritance. Think of them as maps with typed values of different types (which is what they are in JSON). In accordance with this philosophy, all fields are public. Builder-style setters are provided for convenience.

Furthermore, there is no coherence validation. Krypton will not complain that a property reserved for schemas of type string (e.g. minLength) have a value while the type property has the value object, just as JSON would not complain.

JSON arrays are deserialized into either Lists or Sets depending on the semantic of the value in the specification. If the specification requires the values to be unique (e.g. required), then it is a Set. Mind that this means duplicates and order are not preserved upon deserialization.

Type mapping

The types of the fields match the types defined in the spec with the following mapping:

Type in spec	Type in Krypton
string	String
integer	BigInteger
number	BigDecimal
boolean	Boolean

• | Object T | T [T] | List<T> or Set<T> {T} | Map<String, T> Union | Specific class

Union types

Union types are modeled using specific classes that have as many fields as the union supports. Those classes expose utility methods to help distinguish between the different cases.

Roadmap

• Validation

Change log

The versioning follows semantic versioning.

1.1.0

• feat: serialization support
• fix: added patternProperties
• refactor: separated toJson from toString in SimpleType
  • This makes things clearer. toString will get back its default behavior in 2.0.
• refactor: renamed convenience methods in Items
  • Older names remain but are deprecated and will be removed in 2.0.

1.0.1

• fix: correct deserialization of SimpleType
  • The deserialized value was always ARRAY

1.0.0

• feat: 100% spec support (i.e. should deserialize any valid schema)

Edit: it was found later that the patternProperties field was missing from the Schema class. It was added in 1.1.0.