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Validation

This utility provides JSON Schema validation for payloads held within events and response used in AWS Lambda.

Key features

  • Validate incoming events and responses
  • Built-in validation for most common events (API Gateway, SNS, SQS, ...) and support for partial batch failures (SQS, Kinesis)
  • JMESPath support validate only a sub part of the event

Install

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<dependencies>
    ...
    <dependency>
        <groupId>software.amazon.lambda</groupId>
        <artifactId>powertools-validation</artifactId>
        <version>2.11.0</version>
    </dependency>
    ...
</dependencies>
...
<!-- configure the aspectj-maven-plugin to compile-time weave (CTW) the aws-lambda-powertools-java aspects into your project -->
<!-- Note: This AspectJ configuration is not needed when using the functional approach with ValidationUtils.validate() -->
<build>
    <plugins>
        ...
        <plugin>
             <groupId>dev.aspectj</groupId>
             <artifactId>aspectj-maven-plugin</artifactId>
             <version>1.14</version>
             <configuration>
                 <source>17</source> <!-- or higher -->
                 <target>17</target> <!-- or higher -->
                 <complianceLevel>17</complianceLevel> <!-- or higher -->
                 <aspectLibraries>
                     <aspectLibrary>
                         <groupId>software.amazon.lambda</groupId>
                         <artifactId>powertools-validation</artifactId>
                     </aspectLibrary>
                 </aspectLibraries>
             </configuration>
            <dependencies>
                <dependency>
                    <groupId>org.aspectj</groupId>
                    <artifactId>aspectjtools</artifactId>
                    <!-- AspectJ compiler version, in sync with runtime -->
                    <version>1.9.22</version>
                </dependency>
            </dependencies>
             <executions>
                 <execution>
                     <goals>
                         <goal>compile</goal>
                     </goals>
                 </execution>
             </executions>
        </plugin>
        ...
    </plugins>
</build>

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    plugins {
        id 'java'
        id 'io.freefair.aspectj.post-compile-weaving' version '8.1.0' // Not needed when using the functional approach with ValidationUtils.validate()
    }

    repositories {
        mavenCentral()
    }

    dependencies {
        aspect 'software.amazon.lambda:powertools-validation:2.11.0' // Not needed when using the functional approach with ValidationUtils.validate()
        implementation 'software.amazon.lambda:powertools-validation:2.11.0' // Use this instead of 'aspect' when using the functional approach
    }

    sourceCompatibility = 17 // or higher
    targetCompatibility = 17 // or higher

Validating events

You can validate inbound and outbound events using either the @Validation annotation or the functional approach with ValidationUtils.validate() methods:

  • @Validation annotation - Simpler syntax with automatic validation, but requires AspectJ configuration
  • ValidationUtils.validate() - No AspectJ required, provides more control over the validation process such as handling validation errors

We support JSON schema version 4, 6, 7, 2019-09 and 2020-12 using the NetworkNT JSON Schema Validator (Compatibility with JSON Schema versions).

The validator is configured to enable format assertions by default even for 2019-09 and 2020-12. Schemas referenced with a remote $ref (for example https://example.com/schema.json) are fetched over the network.

Powertools now uses NetworkNT JSON Schema Validator 2.x

This changes some types in the public API and the format of validation errors. See Migrating to json-schema-validator 2.x.

When validation fails, the ValidationException message contains the validation errors serialized as JSON. See Validation error format for an example.

Validation annotation

The @Validation annotation is used to validate either inbound events or functions' response.

It will fail fast if an event or response doesn't conform with given JSON Schema. For most type of events a ValidationException will be thrown.

For API gateway events associated with REST APIs and HTTP APIs - APIGatewayProxyRequestEvent and APIGatewayV2HTTPEvent - the @Validation annotation will build and return a custom 400 / "Bad Request" response, with a body containing the validation errors. This saves you from having to catch the validation exception and map it back to a meaningful user error yourself.

For SQS and Kinesis events - SQSEvent and KinesisEvent- the @Validation annotation will add the invalid messages to the batch item failures list in the response, respectively SQSBatchResponse and StreamsEventResponse and removed from the event so that you do not process them within the handler.

While it is easier to specify a json schema file in the classpath (using the notation "classpath:/path/to/schema.json"), you can also provide a JSON String containing the schema.

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import software.amazon.lambda.powertools.validation.Validation;

public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    @Override
    @Validation(inboundSchema = "classpath:/schema_in.json", outboundSchema = "classpath:/schema_out.json")
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        // ...
        return something;
    }
}

NOTE: It's not a requirement to validate both inbound and outbound schemas - You can either use one, or both.

Functional approach with ValidationUtils

The ValidationUtils.validate() method provides a functional approach that can be used within the Lambda handler or any other methods that perform data validation. This approach does not require AspectJ configuration.

With this approach, you can gracefully handle schema validation errors by catching ValidationException.

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import static software.amazon.lambda.powertools.validation.ValidationUtils.*;

public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    @Override
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        try {
            validate(input, "classpath:/schema.json");
        } catch (ValidationException ex) {
            // do something before throwing it
            throw ex;
        }

        // ...
        return something;
    }
}

NOTE: Schemas are stored in memory for reuse, to avoid loading them from file each time.

Built-in events and responses

For the following events and responses, the Validator will automatically perform validation on the content.

Events

Type of event Class Path to content
API Gateway REST APIGatewayProxyRequestEvent body
API Gateway HTTP APIGatewayV2HTTPEvent body
Application Load Balancer ApplicationLoadBalancerRequestEvent body
Cloudformation Custom Resource CloudFormationCustomResourceEvent resourceProperties
CloudWatch Logs CloudWatchLogsEvent awslogs.powertools_base64_gzip(data)
EventBridge / Cloudwatch ScheduledEvent detail
Kafka KafkaEvent records[*][*].value
Kinesis KinesisEvent Records[*].kinesis.powertools_base64(data)
Kinesis Firehose KinesisFirehoseEvent Records[*].powertools_base64(data)
Kinesis Analytics from Firehose KinesisAnalyticsFirehoseInputPreprocessingEvent Records[*].powertools_base64(data)
Kinesis Analytics from Streams KinesisAnalyticsStreamsInputPreprocessingEvent Records[*].powertools_base64(data)
SNS SNSEvent Records[*].Sns.Message
SQS SQSEvent Records[*].body

Responses

Type of response Class Path to content (envelope)
API Gateway REST APIGatewayProxyResponseEvent} body
API Gateway HTTP APIGatewayV2HTTPResponse} body
API Gateway WebSocket APIGatewayV2WebSocketResponse} body
Load Balancer ApplicationLoadBalancerResponseEvent} body
Kinesis Analytics KinesisAnalyticsInputPreprocessingResponse} Records[*].powertools_base64(data)

Custom events and responses

You can also validate any Event or Response type, once you have the appropriate schema.

Sometimes, you might want to validate only a portion of it - This is where the envelope parameter is for.

Envelopes are JMESPath expressions to extract a portion of JSON you want before applying JSON Schema validation.

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import software.amazon.lambda.powertools.validation.Validation;

public class MyCustomEventHandler implements RequestHandler<MyCustomEvent, String> {

    @Override
    @Validation(inboundSchema = "classpath:/my_custom_event_schema.json",
                envelope = "basket.products[*]")
    public String handleRequest(MyCustomEvent input, Context context) {
        return "OK";
    }
}

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{
  "basket": {
    "products" : [
      {
        "id": 43242,
        "name": "FooBar XY",
        "price": 258
      },
      {
        "id": 765,
        "name": "BarBaz AB",
        "price": 43.99
      }
    ]
  }
}

This is quite powerful because you can use JMESPath Query language to extract records from arrays, slice and dice, to pipe expressions and function expressions, where you'd extract what you need before validating the actual payload.

Change the schema version

By default, powertools-validation is configured to use draft 7 (SpecificationVersion.DRAFT_7) as the default dialect if $schema is not explicitly specified within the schema. If $schema is explicitly specified within the schema, the validator will use the specified dialect.

You can use the ValidationConfig to change that behaviour.

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...
import com.networknt.schema.SpecificationVersion;
import software.amazon.lambda.powertools.validation.ValidationConfig;
import software.amazon.lambda.powertools.validation.Validation;

static {
    ValidationConfig.get().setSchemaVersion(SpecificationVersion.DRAFT_4);
}

public class MyXMLEventHandler implements RequestHandler<MyEventWithXML, String> {

    @Override
    @Validation(inboundSchema="classpath:/schema.json", envelope="powertools_xml(path.to.xml_data)")
    public String handleRequest(MyEventWithXML myEvent, Context context) {
        return "OK";
   }
}

Advanced ObjectMapper settings

If you need to configure the Jackson ObjectMapper, you can use the ValidationConfig:

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...
import software.amazon.lambda.powertools.validation.ValidationConfig;
import software.amazon.lambda.powertools.validation.Validation;

static {
    ObjectMapper objectMapper= ValidationConfig.get().getObjectMapper();
    // update (de)serializationConfig or other properties
}

public class MyXMLEventHandler implements RequestHandler<MyEventWithXML, String> {

    @Override
    @Validation(inboundSchema="classpath:/schema.json", envelope="powertools_xml(path.to.xml_data)")
    public String handleRequest(MyEventWithXML myEvent, Context context) {
        return "OK";
   }
}

Migrating to json-schema-validator 2.x

Powertools upgraded NetworkNT JSON Schema Validator from 1.x to 2.x, because upstream no longer releases 1.x. Version 2.0.0 renamed most public types (upstream migration guide). This change ships in version 2.12.0, in line with our dependency lifecycle policy.

You need to change your code only if you:

  • reference com.networknt.schema types directly, or set @Validation(schemaVersion = ...);
  • call ValidationConfig.get().getSchemaVersion(), setSchemaVersion(...) or getFactory();
  • call ValidationUtils.getJsonSchema(...) or a ValidationUtils.validate(...) overload that takes a schema;
  • read ValidationUtils.ValidationErrors or catch JsonSchemaException;
  • parse the ValidationException message or the API Gateway 400 response body.

Everyone else needs no changes.

Renamed types

Before (1.x) After (2.x)
SpecVersion.VersionFlag SpecificationVersion
V4, V6, V7, V201909, V202012 DRAFT_4, DRAFT_6, DRAFT_7, DRAFT_2019_09, DRAFT_2020_12
JsonSchemaFactory (ValidationConfig.getFactory()) SchemaRegistry
JsonSchema Schema
Set<ValidationMessage> (ValidationErrors.getValidationErrors()) List<Error>
JsonSchemaException SchemaException 
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import com.networknt.schema.SpecVersion;

public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
    static {
        ValidationConfig.get().setSchemaVersion(SpecVersion.VersionFlag.V4);
    }

    @Override
    @Validation(inboundSchema = "classpath:/schema_in.json",
                schemaVersion = SpecVersion.VersionFlag.V202012)
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        // ...
    }
}

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import com.networknt.schema.SpecificationVersion;

public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
    static {
        ValidationConfig.get().setSchemaVersion(SpecificationVersion.DRAFT_4);
    }

    @Override
    @Validation(inboundSchema = "classpath:/schema_in.json",
                schemaVersion = SpecificationVersion.DRAFT_2020_12)
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        // ...
    }
}

Validation error format

The ValidationException message is also the body of the 400 response that @Validation returns for API Gateway events. In 2.x, keyword replaces the type and code fields, and message no longer starts with the instance location. The location is still available in instanceLocation.

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{
  "validationErrors": [
    {
      "type": "exclusiveMinimum",
      "code": "1039",
      "message": "/price: must have an exclusive minimum value of 0",
      "instanceLocation": "/price",
      "evaluationPath": "/properties/price/exclusiveMinimum",
      "schemaLocation": "http://example.com/product.json#/properties/price/exclusiveMinimum",
      "messageKey": "exclusiveMinimum",
      "arguments": ["0"]
    }
  ]
}

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{
  "validationErrors": [
    {
      "keyword": "exclusiveMinimum",
      "instanceLocation": "/price",
      "message": "must have an exclusive minimum value of 0",
      "evaluationPath": "/properties/price/exclusiveMinimum",
      "schemaLocation": "http://example.com/product.json#/properties/price/exclusiveMinimum",
      "messageKey": "exclusiveMinimum",
      "arguments": ["0"]
    }
  ]
}

Unchanged behavior

Powertools keeps the 1.x defaults where 2.x changed them:

  • Draft 7 remains the default schema version.
  • Format assertions remain enabled, including for 2019-09 and 2020-12.
  • Remote $ref fetching remains enabled.

Advanced

Lambda SnapStart priming

The Validation utility integrates with AWS Lambda SnapStart to improve restore durations. To make sure the SnapStart priming logic of this utility runs correctly, you need an explicit reference to ValidationConfig in your code to allow the library to register before SnapStart takes a memory snapshot. Learn more about what priming is in this blog post.

If you don't set a custom ValidationConfig in your code yet, make sure to reference ValidationConfig in your Lambda handler initialization code. This can be done by adding one of the following lines to your handler class:

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import software.amazon.lambda.powertools.validation.Validation;
import software.amazon.lambda.powertools.validation.ValidationConfig;

public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    public MyFunctionHandler() {
        ValidationConfig.get(); // Ensure ValidationConfig is loaded for SnapStart
    }

    @Override
    @Validation(inboundSchema = "classpath:/schema_in.json", outboundSchema = "classpath:/schema_out.json")
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        // ...
        return something;
    }
}

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import software.amazon.lambda.powertools.validation.Validation;
import software.amazon.lambda.powertools.validation.ValidationConfig;

public class MyFunctionHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    static {
        ValidationConfig.get(); // Ensure ValidationConfig is loaded for SnapStart
    }

    @Override
    @Validation(inboundSchema = "classpath:/schema_in.json", outboundSchema = "classpath:/schema_out.json")
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
        // ...
        return something;
    }
}