feat: Support CRaC priming of powertools validation (#2081)

* feat: support CRaC priming of powertools validation

- Add org.crac dependency and generate-classesloaded-file profile in pom.xml
- Add classesloaded.txt in src/main/resources for automatic class preloading
- Update ValidationConfig to register for Crac resource
- Update spotbugs-exclude.xml to suppress RV_RETURN_VALUE_IGNORED_NO_SIDE_EFFECT spotbug error in beforeCheckpoint method

* test: add ValidationConfigTest to assert beforeCheckpoint and afterRestore hooks do not throw exception

* docs: Add SnapStart priming subsection for validation

* test: Remove public modifier from ValidationConfigTest class and methods

* docs: Improve Lambda SnapStart priming section

Co-authored-by: Philipp Page <[email protected]>

---------

Co-authored-by: Philipp Page <[email protected]>

Author: kjswaruph

docs/utilities/validation.md

@@ -292,3 +292,53 @@ If you need to configure the Jackson ObjectMapper, you can use the `ValidationCo
        }
     }
     ```
+
+## 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](https://aws.amazon.com/blogs/compute/optimizing-cold-start-performance-of-aws-lambda-using-advanced-priming-strategies-with-snapstart/){target="_blank"}.
+
+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:
+
+=== "Constructor"
+
+    ```java hl_lines="7"
+    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;
+        }
+    }
+    ```
+
+=== "Static Initializer"
+
+    ```java hl_lines="7"
+    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;
+        }
+    }
+    ```

powertools-validation/pom.xml

@@ -71,6 +71,10 @@
             <groupId>com.amazonaws</groupId>
             <artifactId>aws-lambda-java-serialization</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.crac</groupId>
+            <artifactId>crac</artifactId>
+        </dependency>
 
         <!-- Test dependencies -->
         <dependency>
@@ -119,4 +123,25 @@
             <scope>test</scope>
         </dependency>
     </dependencies>
+
+    <profiles>
+        <profile>
+            <id>generate-classesloaded-file</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-surefire-plugin</artifactId>
+                        <configuration>
+                            <argLine>
+                                -Xlog:class+load=info:classesloaded.txt
+                                --add-opens java.base/java.util=ALL-UNNAMED
+                                --add-opens java.base/java.lang=ALL-UNNAMED
+                            </argLine>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
 </project>

powertools-validation/src/main/java/software/amazon/lambda/powertools/validation/ValidationConfig.java

@@ -16,10 +16,15 @@
 
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.networknt.schema.JsonSchema;
 import com.networknt.schema.JsonSchemaFactory;
 import com.networknt.schema.SpecVersion;
 import io.burt.jmespath.JmesPath;
 import io.burt.jmespath.function.BaseFunction;
+import org.crac.Context;
+import org.crac.Core;
+import org.crac.Resource;
+import software.amazon.lambda.powertools.common.internal.ClassPreLoader;
 import software.amazon.lambda.powertools.utilities.JsonConfig;
 import software.amazon.lambda.powertools.utilities.jmespath.Base64Function;
 import software.amazon.lambda.powertools.utilities.jmespath.Base64GZipFunction;
@@ -31,10 +36,15 @@
  * For everything but the validation features (factory, schemaVersion), {@link ValidationConfig}
  * is just a wrapper of {@link JsonConfig}.
  */
-public class ValidationConfig {
+public class ValidationConfig implements Resource {
     private SpecVersion.VersionFlag jsonSchemaVersion = SpecVersion.VersionFlag.V7;
     private JsonSchemaFactory factory = JsonSchemaFactory.getInstance(jsonSchemaVersion);
 
+    // Static block to ensure CRaC registration happens at class loading time
+    static {
+        Core.getGlobalContext().register(get());
+    }
+
     private ValidationConfig() {
     }
 
@@ -102,6 +112,26 @@ public ObjectMapper getObjectMapper() {
         return JsonConfig.get().getObjectMapper();
     }
 
+    @Override
+    public void beforeCheckpoint(Context<? extends Resource> context) throws Exception {
+        // Initialize key components
+        getObjectMapper();
+        getJmesPath();
+        getFactory();
+
+        // Dummy validation
+        String sampleSchema = "{\"type\":\"object\"}";
+        JsonSchema schema = ValidationUtils.getJsonSchema(sampleSchema);
+        ValidationUtils.validate("{\"test\":\"dummy\"}", schema);
+
+        ClassPreLoader.preloadClasses();
+    }
+
+    @Override
+    public void afterRestore(Context<? extends Resource> context) throws Exception {
+        // No action needed after restore
+    }
+
     private static class ConfigHolder {
         private static final ValidationConfig instance = new ValidationConfig();
     }