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title Validation
description Utility

import Note from "../../src/components/Note"

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, ...)
  • JMESPath support validate only a sub part of the event

Install

To install this utility, add the following dependency to your project.

<dependency>
    <groupId>software.amazon.lambda</groupId>
    <artifactId>powertools-validation</artifactId>
    <version>1.1.0</version>
</dependency>

And configure the aspectj-maven-plugin to compile-time weave (CTW) the aws-lambda-powertools-java aspects into your project. You may already have this plugin in your pom. In that case add the dependency to the aspectLibraries section.

<build>
    <plugins>
        ...
        <plugin>
             <groupId>org.codehaus.mojo</groupId>
             <artifactId>aspectj-maven-plugin</artifactId>
             <version>1.11</version>
             <configuration>
                 <source>1.8</source>
                 <target>1.8</target>
                 <complianceLevel>1.8</complianceLevel>
                 <aspectLibraries>
                    <!--    highlight-start    -->
                     <aspectLibrary>
                         <groupId>software.amazon.lambda</groupId>
                         <artifactId>powertools-validation</artifactId>
                     </aspectLibrary>
                     <!--    highlight-end    -->
                 </aspectLibraries>
             </configuration>
             <executions>
                 <execution>
                     <goals>
                         <goal>compile</goal>
                     </goals>
                 </execution>
             </executions>
        </plugin>
        ...
    </plugins>
</build>

Validating events

You can validate inbound and outbound events using @Validation annotation.

You can also use the Validator#validate() methods, if you want more control over the validation process such as handling a validation error.

We support JSON schema version 4, 6, 7 and 201909 (from jmespath-jackson library).

@Validation annotation

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

It will fail fast with ValidationException if an event or response doesn't conform with given JSON Schema.

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.

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.

Validate function

Validate standalone function is used within the Lambda handler, or any other methods that perform data validation.

You can also gracefully handle schema validation errors by catching ValidationException.

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.

Here is a custom event where we only want to validate each products:

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

Here is how you'd use the envelope parameter to extract the payload inside the products key before validating:

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";
    }
}

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.

JMESPath functions

JMESPath functions ensure to make an operation on a specific part of the json.validate

Powertools provides two built-in functions:

powertools_base64 function

Use powertools_base64 function to decode any base64 data.

This sample will decode the base64 value within the data key, and decode the JSON string into a valid JSON before we can validate it:

{
   "data" : "ewogICJpZCI6IDQzMjQyLAogICJuYW1lIjogIkZvb0JhciBYWSIsCiAgInByaWNlIjogMjU4Cn0="
}
public class MyEventHandler implements RequestHandler<MyEvent, String> {

    @Override
    public String handleRequest(MyEvent myEvent, Context context) {
        validate(myEvent, "classpath:/schema.json", "powertools_base64(data)");
        return "OK";
   }
}

powertools_base64_gzip function

Use powertools_base64_gzip function to decompress and decode base64 data.

This sample will decompress and decode base64 data:

{
   "data" : "H4sIAAAAAAAA/6vmUlBQykxRslIwMTYyMdIBcfMSc1OBAkpu+flOiUUKEZFKYOGCosxkkLiRqQVXLQDnWo6bOAAAAA=="
}
public class MyEventHandler implements RequestHandler<MyEvent, String> {

    @Override
    public String handleRequest(MyEvent myEvent, Context context) {
        validate(myEvent, "classpath:/schema.json", "powertools_base64_gzip(data)");
        return "OK";
   }
}

NOTE: You don't need any function to transform a JSON String into a JSON object, powertools-validation will do it for you. In the 2 previous example, data contains JSON. Just provide the function to transform the base64 / gzipped / ... string into a clear JSON string.

Bring your own JMESPath function

This should only be used for advanced use cases where you have special formats not covered by the built-in functions. New functions will be added to the 2 built-in ones.

Your function must extend io.burt.jmespath.function.BaseFunction, take a String as parameter and return a String. You can read the doc for more information.

Here is an example that takes some xml and transform it into json:

public class XMLFunction extends BaseFunction {
    public Base64Function() {
        super("powertools_xml", ArgumentConstraints.typeOf(JmesPathType.STRING));
    }

    @Override
    protected <T> T callFunction(Adapter<T> runtime, List<FunctionArgument<T>> arguments) {
        T value = arguments.get(0).value();
        String xmlString = runtime.toString(value);

        String jsonString =  // ... transform xmlString to json

        return runtime.createString(jsonString);
    }
}

Once your function is created, you need to add it to powertools:

ValidationConfig.get().addFunction(new XMLFunction());

You can then use it to do your validation:

public class MyXMLEventHandler implements RequestHandler<MyEventWithXML, String> {

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

or using annotation:

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";
   }
}

Change the schema version

By default, powertools-validation is configured with V7. You can use the ValidationConfig to change that behaviour:

ValidationConfig.get().setSchemaVersion(SpecVersion.VersionFlag.V4);

Advanced ObjectMapper settings

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

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