BeanInstantiationException when a class extends from MicronautRequestHandler

I am recursively getting below error when it's going to init the bean extends from MicronautRequestHandler. But it's not the case for other regular beans.

Java version: 17
Micronaut : 3.10.0 (I tried 4.1.0 and downgraded to lower version to check)

My simplified version of the Handler class as below : (I removed all the injected services as well to simplify)

package org.example;

import com.amazonaws.services.lambda.runtime.events.S3Event;
import io.micronaut.function.aws.MicronautRequestHandler;
import jakarta.inject.Inject;
import jakarta.inject.Singleton;

@Singleton
public class Handler extends MicronautRequestHandler<S3Event, Void> {

    @Inject
    public Handler() {
        // NOP
    }

    @Override
    public Void execute(S3Event input) {
        System.out.println("Received S3 event: " + input);
        return null;
    }
}

To re-create this locally without Lambda, I created this main method. This is the minimal version of the main LocalRunner class, which still cause the issue.

   package org.example;

import io.micronaut.context.ApplicationContext;

public class LocalRunner {
    public static void main(String[] args) {
        // Start the Micronaut application context
        try (ApplicationContext context = ApplicationContext.run()) {
            // Instantiate your handler class
            Handler handler = context.getBean(Handler.class);
        }
    }

}

I am getting the same error when it deploy to Lambda and trigger with a S3Event.

My build gradle file:

plugins {
    id("application")
}

version = "0.1"
group = "org.example"

repositories {
    mavenCentral()
    maven { url "https://s01.oss.sonatype.org/content/repositories/releases/" }
}

dependencies {
    annotationProcessor("io.micronaut:micronaut-http-validation:3.10.0")
    annotationProcessor("io.micronaut:micronaut-inject-java:3.10.0")
    implementation('io.micronaut.aws:micronaut-function-aws:3.18.0')
    implementation("io.micronaut:micronaut-inject:3.10.0")
    implementation("io.micronaut:micronaut-http-server-netty:3.10.0")
    implementation("io.micronaut:micronaut-json-core:3.10.0")
    implementation("io.micronaut:micronaut-jackson-databind:3.10.0")
    implementation("jakarta.inject:jakarta.inject-api:2.0.1")
    implementation("com.amazonaws:aws-lambda-java-events:3.11.0")
    implementation("software.amazon.awssdk:s3:2.29.0")
    implementation("com.fasterxml.jackson.dataformat:jackson-dataformat-csv:2.16.0")
    implementation("com.fasterxml.jackson.dataformat:jackson-dataformat-yaml:2.16.0")

    // https://mvnrepository.com/artifact/org.slf4j/slf4j-api
    implementation 'org.slf4j:slf4j-api:1.2.13'
    //https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-slf4j-impl
    runtimeOnly("org.apache.logging.log4j:log4j-to-slf4j:2.18.0") 

    //JDBC
    implementation 'com.amazon.redshift:redshift-jdbc42:2.1.0.9'
    implementation 'commons-dbcp:commons-dbcp:1.4'

}
configurations {
    all*.exclude group: 'ch.qos.logback'
    all*.exclude group: 'org.apache.logging.log4j', module: 'log4j-to-slf4j'
}
java {
    sourceCompatibility = JavaVersion.toVersion("17")
    targetCompatibility = JavaVersion.toVersion("17")
}

piece of the error log (repeating it many times):

Path Taken: new Handler()
    ... 1024 more
Caused by: io.micronaut.context.exceptions.BeanInstantiationException: Bean 
definition [org.example.Handler] could not be loaded:

//...

    at org.example.Handler.<init>(Handler.java:12)
    at org.example.$Handler$Definition.build(Unknown Source)
    at io.micronaut.context.DefaultBeanContext.resolveByBeanFactory(DefaultBeanContext.java:2354)
    at io.micronaut.context.DefaultBeanContext.doCreateBean(DefaultBeanContext.java:2305)
    at io.micronaut.context.DefaultBeanContext.doCreateBean(DefaultBeanContext.java:2251)
    at io.micronaut.context.DefaultBeanContext.createRegistration(DefaultBeanContext.java:3016)
    at io.micronaut.context.SingletonScope.getOrCreate(SingletonScope.java:80)
    at io.micronaut.context.DefaultBeanContext.findOrCreateSingletonBeanRegistration(DefaultBeanContext.java:2918)
    at io.micronaut.context.DefaultBeanContext.loadContextScopeBean(DefaultBeanContext.java:2746)
    at io.micronaut.context.DefaultBeanContext.initializeContext(DefaultBeanContext.java:1915)
    at io.micronaut.context.DefaultApplicationContext.initializeContext(DefaultApplicationContext.java:249)
    at io.micronaut.context.DefaultBeanContext.readAllBeanDefinitionClasses(DefaultBeanContext.java:3326)
    at io.micronaut.context.DefaultBeanContext.finalizeConfiguration(DefaultBeanContext.java:3684)
    at io.micronaut.context.DefaultBeanContext.start(DefaultBeanContext.java:341)
    at io.micronaut.context.DefaultApplicationContext.start(DefaultApplicationContext.java:194)
    at io.micronaut.function.executor.AbstractExecutor.startEnvironment(AbstractExecutor.java:124)
    at io.micronaut.function.aws.MicronautRequestHandler.buildApplicationContext(MicronautRequestHandler.java:222)
    at io.micronaut.function.aws.MicronautRequestHandler.<init>(MicronautRequestHandler.java:108)
    at org.example.Handler.<init>(Handler.java:12)
    at org.example.$Handler$Definition.build(Unknown Source)
    at io.micronaut.context.DefaultBeanContext.resolveByBeanFactory(DefaultBeanContext.java:2354)
    at io.micronaut.context.DefaultBeanContext.doCreateBean(DefaultBeanContext.java:2305)
    at io.micronaut.context.DefaultBeanContext.doCreateBean(DefaultBeanContext.java:2251)
    at io.micronaut.context.DefaultBeanContext.createRegistration(DefaultBeanContext.java:3016)
    at io.micronaut.context.SingletonScope.getOrCreate(SingletonScope.java:80)
    at io.micronaut.context.DefaultBeanContext.findOrCreateSingletonBeanRegistration(DefaultBeanContext.java:2918)
    at io.micronaut.context.DefaultBeanContext.loadContextScopeBean(DefaultBeanContext.java:2746)
    at io.micronaut.context.DefaultBeanContext.initializeContext(DefaultBeanContext.java:1915)
    at io.micronaut.context.DefaultApplicationContext.initializeContext(DefaultApplicationContext.java:249)
    at io.micronaut.context.DefaultBeanContext.readAllBeanDefinitionClasses(DefaultBeanContext.java:3326)
    at io.micronaut.context.DefaultBeanContext.finalizeConfiguration(DefaultBeanContext.java:3684)
    at io.micronaut.context.DefaultBeanContext.start(DefaultBeanContext.java:341)
    at io.micronaut.context.DefaultApplicationContext.start(DefaultApplicationContext.java:194)
    at io.micronaut.function.executor.AbstractExecutor.startEnvironment(AbstractExecutor.java:124)
    at io.micronaut.function.aws.MicronautRequestHandler.buildApplicationContext(MicronautRequestHandler.java:222)
    at io.micronaut.function.aws.MicronautRequestHandler.<init>(MicronautRequestHandler.java:108)
    at org.example.Handler.<init>(Handler.java:12)

resolveByBeanFactory() is trying again to initialize the constructor , so it's recursively go in the circle.

UPDATE

I was able to re-create the issue with a fresh IntelliJ-Micronaut default project (Java 17, Micronaut 4.4.2) with 3 simple steps.

Append these 2 dependencies to your build.gradle

implementation('io.micronaut.aws:micronaut-function-aws')
implementation("com.amazonaws:aws-lambda-java-events:3.11.0")

Add the above simple Handler class
Add these 2 lines to your Application.java after Micronaut.run

public class Application {

   public static void main(String[] args) {
       Micronaut.run(Application.class, args);
       try (ApplicationContext context = ApplicationContext.run()) {
           Handler handler = context.getBean(Handler.class);
       }
   }
}

Solution

I finally found the issue. A tiny little mistake cause this all :-(

Never Use @Singleton on the Lambda Handler class!

Here’s why:

In Micronaut, @Singleton registers the class as a bean in the application context, which works well for services and other components. However, the Lambda Handler class (which extends MicronautRequestHandler here) shouldn’t be a singleton, as it is treated differently from other beans. Using @Singleton on the handler can lead to initialization issues and cause dependency injection to fail.

Solution:

Simply remove the @Singleton annotation from your handler class, and let Micronaut handle it as a Lambda function rather than as an application bean.