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This is a Java implementation of the JSON Schema Core Draft v4, v6, v7, v2019-09 and v2020-12 specification for JSON schema validation. This implementation supports Customizing Meta-Schemas, Vocabularies, Keywords and Formats.

In addition, OpenAPI 3 request/response validation is supported with the use of the appropriate meta-schema. For users who want to collect information from a JSON node based on the schema, the walkers can help. The JSON parser used is the Jackson parser. As it is a key component in our light-4j microservices framework to validate request/response against OpenAPI specification for light-rest-4j and RPC schema for light-hybrid-4j at runtime, performance is the most important aspect in the design.

Information on the compatibility support for each version, including known issues, can be found in the Compatibility with JSON Schema versions document.

Since Draft 2019-09 the format keyword only generates annotations by default and does not generate assertions.

This behavior can be overridden to generate assertions by setting the setFormatAssertionsEnabled to true in SchemaValidatorsConfig or ExecutionConfig.

This library can contain breaking changes in minor version releases that may require code changes.

Information on notable or breaking changes when upgrading the library can be found in the Upgrading to new versions document.

The Releases page will contain information on the latest versions.

The JSON Schema Validation Comparison project from Creek has an informative Comparison of JVM based Schema Validation Implementations which compares both the functional and performance characteristics of a number of different Java implementations.

• Functional comparison
• Performance comparison

The Bowtie project has a report that compares functional characteristics of different implementations, including non-Java implementations, but does not do any performance benchmarking.

This should be the fastest Java JSON Schema Validator implementation.

The following is the benchmark results from the JSON Schema Validator Perftest project that uses the Java Microbenchmark Harness.

Note that the benchmark results are highly dependent on the input data workloads and schemas used for the validation.

In this case this workload is using the Draft 4 specification and largely tests the performance of the evaluating the properties keyword. You may refer to Results of performance comparison of JVM based JSON Schema Validation Implementations for benchmark results for more typical workloads

If performance is an important consideration, the specific sample workloads should be benchmarked, as there are different performance characteristics when certain keywords are used. For instance the use of the unevaluatedProperties or unevaluatedItems keyword will trigger annotation collection in the related validators, such as the properties or items validators, and annotation collection will adversely affect performance.

Benchmark                                            Mode  Cnt      Score    Error   Units
NetworkntBenchmark.testValidate                     thrpt   10   8352.126 ± 61.870   ops/s
NetworkntBenchmark.testValidate:gc.alloc.rate       thrpt   10    721.296 ±  5.342  MB/sec
NetworkntBenchmark.testValidate:gc.alloc.rate.norm  thrpt   10  90560.013 ±  0.001    B/op
NetworkntBenchmark.testValidate:gc.count            thrpt   10     61.000           counts
NetworkntBenchmark.testValidate:gc.time             thrpt   10     68.000               ms

Benchmark                                            Mode  Cnt       Score    Error   Units
EveritBenchmark.testValidate                        thrpt   10    3775.453 ± 44.023   ops/s
EveritBenchmark.testValidate:gc.alloc.rate          thrpt   10    1667.345 ± 19.437  MB/sec
EveritBenchmark.testValidate:gc.alloc.rate.norm     thrpt   10  463104.030 ±  0.003    B/op
EveritBenchmark.testValidate:gc.count               thrpt   10     140.000           counts
EveritBenchmark.testValidate:gc.time                thrpt   10     158.000               ms

This implementation is tested against the JSON Schema Test Suite. As tests are continually added to the suite, these test results may not be current.

• Note that this uses the JoniRegularExpressionFactory for the pattern and format regex tests.

This library uses Jackson which is a Java JSON parser that is widely used in other projects. If you are already using the Jackson parser in your project, it is natural to choose this library over others for schema validation.

The library works with JSON and YAML on both schema definitions and input data.

The OpenAPI 3.0 specification is using JSON schema to validate the request/response, but there are some differences. With a configuration file, you can enable the library to work with OpenAPI 3.0 validation.

Following the design principle of the Light Platform, this library has minimal dependencies to ensure there are no dependency conflicts when using it.

The following are the dependencies that will automatically be included when this library is included.

<dependency>
    <!-- Used for logging -->
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>${version.slf4j}</version>
</dependency>

<dependency>
    <!-- Used to process JSON -->
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>${version.jackson}</version>
</dependency>

<dependency>
    <!-- Used to process YAML -->
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-yaml</artifactId>
    <version>${version.jackson}</version>
</dependency>

<dependency>
    <!-- Used to validate RFC 3339 date and date-time -->
    <groupId>com.ethlo.time</groupId>
    <artifactId>itu</artifactId>
    <version>${version.itu}</version>
</dependency>

The following are the optional dependencies that may be required for certain options.

These are not automatically included and setting the relevant option without adding the library will result in a ClassNotFoundException.

<dependency>
    <!-- Used to validate ECMA 262 regular expressions -->
    <!-- Approximately 50 MB in dependencies -->
    <!-- GraalJSRegularExpressionFactory -->
    <groupId>org.graalvm.js</groupId>
    <artifactId>js</artifactId>
    <version>${version.graaljs}</version>
</dependency>

<dependency>
    <!-- Used to validate ECMA 262 regular expressions -->
    <!-- Approximately 2 MB in dependencies -->
    <!-- JoniRegularExpressionFactory -->
    <groupId>org.jruby.joni</groupId>
    <artifactId>joni</artifactId>
    <version>${version.joni}</version>
</dependency>

The following are required dependencies that are automatically included, but can be explicitly excluded if they are not required.

The YAML dependency can be excluded if this is not required. Attempting to process schemas or input that are YAML will result in a ClassNotFoundException.

<dependency>
    <groupId>com.networknt</groupId>
    <artifactId>json-schema-validator</artifactId>
    <exclusions>
        <exclusion>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-yaml</artifactId>
        </exclusion>
    </exclusions>
</dependency>

The Ethlo Time dependency can be excluded if accurate validation of the date-time format is not required. The date-time format will then use java.time.OffsetDateTime to determine if the date-time is valid .

<dependency>
    <groupId>com.networknt</groupId>
    <artifactId>json-schema-validator</artifactId>
    <exclusions>
        <exclusion>
            <groupId>com.ethlo.time</groupId>
            <artifactId>itu</artifactId>
        </exclusion>
    </exclusions>
</dependency>

This library is very active with a lot of contributors. New features and bug fixes are handled quickly by the team members. Because it is an essential dependency of the light-4j framework in the same GitHub organization, it will be evolved and maintained along with the framework.

The library supports Java 8 and up. If you want to build from the source code, you need to install JDK 8 locally. To support multiple version of JDK, you can use SDKMAN

This package is available on Maven central.

<dependency>
    <groupId>com.networknt</groupId>
    <artifactId>json-schema-validator</artifactId>
    <version>1.5.4</version>
</dependency>

dependencies {
    implementation(group: 'com.networknt', name: 'json-schema-validator', version: '1.5.4');
}

The following example demonstrates how inputs are validated against a schema. It comprises the following steps.

• Creating a schema factory with the default schema dialect and how the schemas can be retrieved.
  • Configuring mapping the $id to a retrieval URI using schemaMappers.
  • Configuring how the schemas are loaded using the retrieval URI using schemaLoaders. For instance a Map<String, String> schemas containing a mapping of retrieval URI to schema data as a String can by configured using builder.schemaLoaders(schemaLoaders -> schemaLoaders.schemas(schemas)). This also accepts a Function<String, String> schemaRetrievalFunction.
• Creating a configuration for controlling validator behavior.
• Loading a schema from a schema location along with the validator configuration.
• Using the schema to validate the data along with setting any execution specific configuration like for instance the locale or whether format assertions are enabled.

// This creates a schema factory that will use Draft 2020-12 as the default if $schema is not specified
// in the schema data. If $schema is specified in the schema data then that schema dialect will be used
// instead and this version is ignored.
JsonSchemaFactory jsonSchemaFactory = JsonSchemaFactory.getInstance(VersionFlag.V202012, builder -> 
    // This creates a mapping from $id which starts with https://www.example.org/ to the retrieval URI classpath:schema/
    builder.schemaMappers(schemaMappers -> schemaMappers.mapPrefix("https://www.example.org/", "classpath:schema/"))
);

SchemaValidatorsConfig.Builder builder = SchemaValidatorsConfig.builder();
// By default the JDK regular expression implementation which is not ECMA 262 compliant is used
// Note that setting this requires including optional dependencies
// builder.regularExpressionFactory(GraalJSRegularExpressionFactory.getInstance());
// builder.regularExpressionFactory(JoniRegularExpressionFactory.getInstance());
SchemaValidatorsConfig config = builder.build();

// Due to the mapping the schema will be retrieved from the classpath at classpath:schema/example-main.json.
// If the schema data does not specify an $id the absolute IRI of the schema location will be used as the $id.
JsonSchema schema = jsonSchemaFactory.getSchema(SchemaLocation.of("https://www.example.org/example-main.json"), config);
String input = "{\r\n"
    + "  \"main\": {\r\n"
    + "    \"common\": {\r\n"
    + "      \"field\": \"invalidfield\"\r\n"
    + "    }\r\n"
    + "  }\r\n"
    + "}";

Set<ValidationMessage> assertions = schema.validate(input, InputFormat.JSON, executionContext -> {
    // By default since Draft 2019-09 the format keyword only generates annotations and not assertions
    executionContext.getExecutionConfig().setFormatAssertionsEnabled(true);
});

The following example demonstrates how a schema is validated against a meta-schema.

This is actually the same as validating inputs against a schema except in this case the input is the schema and the schema used is the meta-schema.

Note that the meta-schemas for Draft 4, Draft 6, Draft 7, Draft 2019-09 and Draft 2020-12 are bundled with the library and these classpath resources will be used by default.

JsonSchemaFactory jsonSchemaFactory = JsonSchemaFactory.getInstance(VersionFlag.V202012);

SchemaValidatorsConfig.Builder builder = SchemaValidatorsConfig.builder();
// By default the JDK regular expression implementation which is not ECMA 262 compliant is used
// Note that setting this requires including optional dependencies
// builder.regularExpressionFactory(GraalJSRegularExpressionFactory.getInstance());
// builder.regularExpressionFactory(JoniRegularExpressionFactory.getInstance());
SchemaValidatorsConfig config = builder.build();

// Due to the mapping the meta-schema will be retrieved from the classpath at classpath:draft/2020-12/schema.
JsonSchema schema = jsonSchemaFactory.getSchema(SchemaLocation.of(SchemaId.V202012), config);
String input = "{\r\n"
    + "  \"type\": \"object\",\r\n"
    + "  \"properties\": {\r\n"
    + "    \"key\": {\r\n"
    + "      \"title\" : \"My key\",\r\n"
    + "      \"type\": \"invalidtype\"\r\n"
    + "    }\r\n"
    + "  }\r\n"
    + "}";
Set<ValidationMessage> assertions = schema.validate(input, InputFormat.JSON, executionContext -> {
    // By default since Draft 2019-09 the format keyword only generates annotations and not assertions
    executionContext.getExecutionConfig().setFormatAssertionsEnabled(true);
});

The following types of results are generated by the library.

The following information is used to describe both types of results.

Assertions contains the following additional information

Annotations contains the following additional information

The library can be configured to store line and column information in the JsonNode instances for the instance and schema nodes. This will adversely affect performance and is not configured by default.

This is done by configuring a JsonNodeReader that uses the LocationJsonNodeFactoryFactoryon the JsonSchemaFactory. The JsonLocation information can then be retrieved using JsonNodes.tokenLocationOf(jsonNode).

String schemaData = "{\r\n"
                + "  \"$id\": \"https://schema/myschema\",\r\n"
                + "  \"properties\": {\r\n"
                + "    \"startDate\": {\r\n"
                + "      \"format\": \"date\",\r\n"
                + "      \"minLength\": 6\r\n"
                + "    }\r\n"
                + "  }\r\n"
                + "}";
String inputData = "{\r\n"
                + "  \"startDate\": \"1\"\r\n"
                + "}";
JsonSchemaFactory factory = JsonSchemaFactory.getInstance(VersionFlag.V202012,
        builder -> builder.jsonNodeReader(JsonNodeReader.builder().locationAware().build()));
SchemaValidatorsConfig config = SchemaValidatorsConfig.builder().build();
JsonSchema schema = factory.getSchema(schemaData, InputFormat.JSON, config);
Set<ValidationMessage> messages = schema.validate(inputData, InputFormat.JSON, executionContext -> {
    executionContext.getExecutionConfig().setFormatAssertionsEnabled(true);
});
List<ValidationMessage> list = messages.stream().collect(Collectors.toList());
ValidationMessage format = list.get(0);
JsonLocation formatInstanceNodeTokenLocation = JsonNodes.tokenLocationOf(format.getInstanceNode());
JsonLocation formatSchemaNodeTokenLocation = JsonNodes.tokenLocationOf(format.getSchemaNode());
ValidationMessage minLength = list.get(1);
JsonLocation minLengthInstanceNodeTokenLocation = JsonNodes.tokenLocationOf(minLength.getInstanceNode());
JsonLocation minLengthSchemaNodeTokenLocation = JsonNodes.tokenLocationOf(minLength.getSchemaNode());

assertEquals("format", format.getType());
assertEquals("date", format.getSchemaNode().asText());
assertEquals(5, formatSchemaNodeTokenLocation.getLineNr());
assertEquals(17, formatSchemaNodeTokenLocation.getColumnNr());
assertEquals("1", format.getInstanceNode().asText());
assertEquals(2, formatInstanceNodeTokenLocation.getLineNr());
assertEquals(16, formatInstanceNodeTokenLocation.getColumnNr());
assertEquals("minLength", minLength.getType());
assertEquals("6", minLength.getSchemaNode().asText());
assertEquals(6, minLengthSchemaNodeTokenLocation.getLineNr());
assertEquals(20, minLengthSchemaNodeTokenLocation.getColumnNr());
assertEquals("1", minLength.getInstanceNode().asText());
assertEquals(2, minLengthInstanceNodeTokenLocation.getLineNr());
assertEquals(16, minLengthInstanceNodeTokenLocation.getColumnNr());
assertEquals(16, minLengthInstanceNodeTokenLocation.getColumnNr());

This library implements the Flag, List and Hierarchical output formats defined in the Specification for Machine-Readable Output for JSON Schema Validation and Annotation.

The List and Hierarchical output formats are particularly helpful for understanding how the system arrived at a particular result.

The following example shows how to generate the hierarchical output format with annotation collection and reporting turned on and format assertions turned on.

JsonSchemaFactory factory = JsonSchemaFactory.getInstance(VersionFlag.V202012);
SchemaValidatorsConfig config = SchemaValidatorsConfig().builder().formatAssertionsEnabled(true).build();
JsonSchema schema = factory.getSchema(SchemaLocation.of("https://json-schema.org/schemas/example"), config);
        
OutputUnit outputUnit = schema.validate(inputData, InputFormat.JSON, OutputFormat.HIERARCHICAL, executionContext -> {
    executionContext.getExecutionConfig().setAnnotationCollectionEnabled(true);
    executionContext.getExecutionConfig().setAnnotationCollectionFilter(keyword -> true);
});

The following is sample output from the Hierarchical format.

{
  "valid" : false,
  "evaluationPath" : "",
  "schemaLocation" : "https://json-schema.org/schemas/example#",
  "instanceLocation" : "",
  "droppedAnnotations" : {
    "properties" : [ "foo", "bar" ],
    "title" : "root"
  },
  "details" : [ {
    "valid" : false,
    "evaluationPath" : "/properties/foo/allOf/0",
    "schemaLocation" : "https://json-schema.org/schemas/example#/properties/foo/allOf/0",
    "instanceLocation" : "/foo",
    "errors" : {
      "required" : "required property 'unspecified-prop' not found"
    }
  }, {
    "valid" : false,
    "evaluationPath" : "/properties/foo/allOf/1",
    "schemaLocation" : "https://json-schema.org/schemas/example#/properties/foo/allOf/1",
    "instanceLocation" : "/foo",
    "droppedAnnotations" : {
      "properties" : [ "foo-prop" ],
      "title" : "foo-title",
      "additionalProperties" : [ "foo-prop", "other-prop" ]
    },
    "details" : [ {
      "valid" : false,
      "evaluationPath" : "/properties/foo/allOf/1/properties/foo-prop",
      "schemaLocation" : "https://json-schema.org/schemas/example#/properties/foo/allOf/1/properties/foo-prop",
      "instanceLocation" : "/foo/foo-prop",
      "errors" : {
        "const" : "must be a constant value 1"
      },
      "droppedAnnotations" : {
        "title" : "foo-prop-title"
      }
    } ]
  }, {
    "valid" : false,
    "evaluationPath" : "/properties/bar/$ref",
    "schemaLocation" : "https://json-schema.org/schemas/example#/$defs/bar",
    "instanceLocation" : "/bar",
    "droppedAnnotations" : {
      "properties" : [ "bar-prop" ],
      "title" : "bar-title"
    },
    "details" : [ {
      "valid" : false,
      "evaluationPath" : "/properties/bar/$ref/properties/bar-prop",
      "schemaLocation" : "https://json-schema.org/schemas/example#/$defs/bar/properties/bar-prop",
      "instanceLocation" : "/bar/bar-prop",
      "errors" : {
        "minimum" : "must have a minimum value of 10"
      },
      "droppedAnnotations" : {
        "title" : "bar-prop-title"
      }
    } ]
  } ]
}

When the library creates a schema from the schema factory, it creates a distinct validator instance for each location on the evaluation path. This means if there are different $ref that reference the same schema location, different validator instances are created for each evaluation path.

When the schema is created, the library will by default automatically preload all the validators needed and resolve references. This can be disabled with the preloadJsonSchema option in the SchemaValidatorsConfig. At this point, no exceptions will be thrown if a reference cannot be resolved. If there are references that are cyclic, only the first cycle will be preloaded. If you wish to ensure that remote references can all be resolved, the initializeValidators method needs to be called on the JsonSchema which will throw an exception if there are references that cannot be resolved.

Instances for JsonSchemaFactory and the JsonSchema created from it are designed to be thread-safe provided its configuration is not modified and should be cached and reused. Not reusing the JsonSchema means that the schema data needs to be repeated parsed with validator instances created and references resolved. When references are resolved, the validators created will be cached. For schemas that have deeply nested references, the memory needed for the validators may be very high, in which case the caching may need to be disabled using the cacheRefs option in the SchemaValidatorsConfig. Disabling this will mean the validators from the references need to be re-created for each validation run which will impact performance.

Collecting annotations will adversely affect validation performance.

The earlier draft specifications contain less keywords that can potentially impact performance. For instance the use of the unevaluatedProperties or unevaluatedItems keyword will trigger annotation collection in the related validators, such as the properties or items validators.

This does not mean that using a schema with a later draft specification will automatically cause a performance impact. For instance, the properties validator will perform checks to determine if annotations need to be collected, and checks if the meta-schema contains the unevaluatedProperties keyword and whether the unevaluatedProperties keyword exists adjacent the evaluation path.

The library assumes that the schemas being loaded are trusted. This security model assumes the use case where the schemas are bundled with the application on the classpath.

The light-rest-4j, light-graphql-4j and light-hybrid-4j use this library to validate the request and response based on the specifications. If you are using other frameworks like Spring Boot, you can use the OpenApiValidator, a generic OpenAPI 3.0 validator based on the OpenAPI 3.0 specification.

If you have a project using this library, please submit a PR to add your project below.

Thanks to the following people who have contributed to this project. If you are using this library, please consider to be a sponsor for one of the contributors.

@stevehu

@prashanth-chaitanya

@fdutton

@valfirst

@BalloonWen

@jiachen1120

@ddobrin

@eskabetxe

@ehrmann

@prashanthjos

@Subhajitdas298

@FWiesner

@rhwood

@jawaff

@nitin1891

For all contributors, please visit https://github.com/networknt/json-schema-validator/graphs/contributors

If you are a contributor, please join the GitHub Sponsors and switch the link to your sponsors dashboard via a PR.