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json-sKema

json-sKema is a Json Schema validator library for the Java Virtual Machine. It implements the draft 2020-12 specification.

Are you new to JSON Schema? Get started with Understanding JSON Schema!

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Installation

Maven

Add the following dependency to the <dependencies> section of your project:

<dependency>
    <groupId>com.github.erosb</groupId>
    <artifactId>json-sKema</artifactId>
    <version>0.18.0</version>
</dependency>

Gradle

dependencies {
    implementation("com.github.erosb:json-sKema:0.18.0")
}

Usage

Hello-world

Complete source

// parse the schema JSON as string
JsonValue schemaJson = new JsonParser("""
{
	"$schema": "https://json-schema.org/draft/2020-12/schema",
	"type": "object",
	"properties": {
		"age": {
			"type": "number",
			"minimum": 0
		},
		"name": {
			"type": "string"
		},
		"email": {
			"type": "string",
			"format": "email"
		}
	}
}
""").parse();
// map the raw json to a reusable Schema instance
Schema schema = new SchemaLoader(schemaJson).load();

// create a validator instance for each validation (one-time use object)
Validator validator = Validator.create(schema, new ValidatorConfig(FormatValidationPolicy.ALWAYS));

// parse the input instance to validate against the schema
JsonValue instance = new JsonParser("""
{
	"age": -5,
	"name": null,
	"email": "invalid"
}
""").parse();

// run the validation
ValidationFailure failure = validator.validate(instance);

// print the validation failures (if any)
System.out.println(failure);

Loading a schema file from URL

// HTTP(s) protocol is also supported
Schema schema = SchemaLoader.forURL("classpath:///path/to/your/schema.json").load();

// create a validator instance for each validation (one-time use object) 
Validator validator = Validator.forSchema(schema);
// ...

Pre-registering schemas by URI before schema loading

Complete source

// Creating a SchemaLoader config with a pre-registered schema by URI
SchemaLoaderConfig config = createDefaultConfig(Map.of(
			// When the loader sees this URI,
			new URI("urn:uuid:d652a438-9897-4160-959c-bbdb690c3e0d"),

			// then it will resolve it to this schema json
			"""
			{
				"$defs": {
					"ItemType": {
						"type": "integer",
						"minimum": 0
					}
				}
			}
			"""
	));
// parsing the schema json, with a $ref to the above pre-configured URI
JsonValue schemaJson = new JsonParser("""
		{
			"type": "array",
			"items": {
				"$ref": "urn:uuid:d652a438-9897-4160-959c-bbdb690c3e0d#/$defs/ItemType"
			}
		}
		""").parse();
// loading the schema json into a Schema object
Schema schema = new SchemaLoader(schemaJson, config).load();

// running the validation
ValidationFailure result = Validator.forSchema(schema).validate(new JsonParser("[null]").parse());
System.out.println(result.toJSON());

Validating in Read or Write context

Complete source

If you want to take advantage of the "readOnly" and "writeOnly" keywords of json schema, you can tell the Validator instance if the validation happens in read or write context:

JsonValue schemaJson = new JsonParser("""
{
    "type": "object",
    "properties": {
        "id": {
            "readOnly": true,
            "type": "number"
        },
        "name": {
            "type": "string"
        },
        "password": {
            "type": "string",
            "writeOnly": true
        }
    }
}
""").parse();
// map the raw json to a reusable Schema instance
Schema schema = new SchemaLoader(schemaJson).load();

// creating write-context validator, it will report validation failures
// for read-only properties that are included in the instance
var writeContextValidator = Validator.create(schema, ValidatorConfig.builder()
        .readWriteContext(ReadWriteContext.WRITE)
        .build()
);

// creating the json document which will be validated (first in write context, then in read context)
JsonValue instance = new JsonParser("""
        {
            "id": 1,
            "name": "John Doe",
            "password": "v3ry_s3cur3"
        }
        """).parse();
var writeContextFailure = writeContextValidator.validate(instance);

// prints failure because the read-only property "id" is present in write context
System.out.println(writeContextFailure);

// creating read-context validator, it will report validation failures
// for write-only properties that are included in the instance
var readContextValidator = Validator.create(schema, ValidatorConfig.builder()
        .readWriteContext(ReadWriteContext.READ)
        .build()
);

var readContextFailure = readContextValidator.validate(instance);

// prints failure because the write-only property "password" is present in read context
System.out.println(readContextFailure);

SchemaBuilder for dynamic (programmatic) schema construction

The library allows dynamic schema construction via its SchemaBuilder class. This is useful in cases when, instead of working with static schemas or externally fed JSON Schemas, the application needs to create a schema instance at run-time, dynamically. This can be done with a fluent API, demonstrated below:

Complete source

import static com.github.erosb.jsonsKema.SchemaBuilder.*;
//...
typeObject()
    .property("myString", typeString()
        .minLength(2)
        .maxLength(50)
        .pattern("^[a-zA-Z ]*$")
    ).property("myInteger", typeInteger()
        .minimum(10)
        .maximum(20)
        .multipleOf(4)
    ).property("myObject", typeObject()
        .additionalProperties(falseSchema())
        .patternProperties(Map.of(
            "^[A-Z]{2}$", allOf(
                typeArray().items(typeNumber())
                    .prefixItems(List.of(typeBoolean(), typeBoolean())),
                typeArray().minContains(3, constSchema(new JsonNumber(1.5)))
            )
        ))
    )

Compatibility notes

The library implements the JSON Schema draft 2020-12 core and validation specifications, with the following notes:

"format" support

The library currently has built-in support for the following "format" values defined in the specification:

<table> <thead> <tr> <td>"format"</td> <td>Supported?</td> <td>Notes</td> </tr> </thead> <tbody> <tr> <td>date</td> <td>Yes</td> <td></td> </tr> <tr> <td>date-time</td> <td>Yes</td> <td>Non-UTC values with leap seconds not supported</td> </tr> <tr> <td>time</td> <td>Yes</td> <td></td> </tr> <tr> <td>duration</td> <td>Partially</td> <td></td> </tr> <tr> <td>email</td> <td>Yes</td> <td>IPV6 domain parts not supported</td> </tr> <tr> <td>uri</td> <td>Yes</td> <td></td> </tr> <tr> <td>ipv4</td> <td>Yes</td> <td></td> </tr> <tr> <td>ipv6</td> <td>Yes</td> <td></td> </tr> <tr> <td>uuid</td> <td>Yes</td> <td></td> </tr> </tbody> </table>

The following formats are NOT supported: hostname, idn-email, idn-hostname, iri, iri-reference, json-pointer, regex, relative-json-pointer, uri-reference, uri-template .

Support for older JSON Schema drafts

This project is the successor of everit-org/json-schema. If you want to use draft-04, draft-06 or draft-07 versions of JSON Schema, then you can use the everit library.

Contribution guideline

Local environment setup:

Prerequisite: JDK and Maven installed

git clone https://github.com/erosb/json-sKema.git
cd json-sKema
git submodule init
git submodule update

Building the project:

mvn clean package

Building the project and running the official test suite:

Test annotated with @Tag("acceptance") require the test suite to be pulled using:

git submodule update --init --recursive

Then run the tests:

mvn clean verify

Building the project without running the official test suite:

mvn clean package -Dgroups='!acceptance'