Aws Lambda Java Integration

# Micronaut Lambda Reference

Complete guide for creating AWS Lambda functions with Micronaut Framework.

## Table of Contents

1. [Project Setup](#project-setup)
2. [Handler Implementation](#handler-implementation)
3. [Cold Start Optimization](#cold-start-optimization)
4. [Dependency Injection](#dependency-injection)
5. [Deployment Configuration](#deployment-configuration)

---

## Project Setup

### Gradle Configuration

```groovy
plugins {
    id("com.github.johnrengelman.shadow") version "8.1.1"
    id("io.micronaut.application") version "4.7.6"
}

version = "1.0.0"
group = "com.example"

repositories {
    mavenCentral()
}

dependencies {
    // Micronaut Lambda
    implementation("io.micronaut.aws:micronaut-function-aws-api-proxy")
    implementation("io.micronaut.aws:micronaut-function-aws-custom-runtime")

    // AWS Lambda Events
    implementation("com.amazonaws:aws-lambda-java-events:3.11.4")
    implementation("com.amazonaws:aws-lambda-java-core:1.2.3")

    // AWS SDK (if needed)
    implementation("software.amazon.awssdk:dynamodb")
    implementation("software.amazon.awssdk:s3")

    // Testing
    testImplementation("io.micronaut.test:micronaut-test-junit5")
    testImplementation("org.junit.jupiter:junit-jupiter")
    testImplementation("org.mockito:mockito-core")
}

application {
    mainClass.set("com.example.Application")
}

java {
    sourceCompatibility = JavaVersion.toVersion("21")
    targetCompatibility = JavaVersion.toVersion("21")
}

micronaut {
    runtime("lambda")
    testRuntime("junit5")
    processing {
        incremental(true)
        annotations("com.example.*")
    }
    aot {
        optimizeClassLoading(true)
        convertYamlToJava(true)
        precomputeOperations(true)
    }
}

tasks.named("shadowJar") {
    archiveClassifier.set("")
    mergeServiceFiles()
}
```

### Maven Configuration

```xml
<project>
    <parent>
        <groupId>io.micronaut</groupId>
        <artifactId>micronaut-parent</artifactId>
        <version>4.7.6</version>
    </parent>

    <groupId>com.example</groupId>
    <artifactId>my-micronaut-lambda</artifactId>
    <version>1.0.0</version>

    <properties>
        <maven.compiler.source>21</maven.compiler.source>
        <maven.compiler.target>21</maven.compiler.target>
        <micronaut.version>4.7.6</micronaut.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>io.micronaut.aws</groupId>
            <artifactId>micronaut-function-aws-api-proxy</artifactId>
        </dependency>
        <dependency>
            <groupId>com.amazonaws</groupId>
            <artifactId>aws-lambda-java-events</artifactId>
            <version>3.11.4</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>io.micronaut.maven</groupId>
                <artifactId>micronaut-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>
```

### Project Structure

```
src/
├── main/
│   ├── java/
│   │   └── com/example/
│   │       ├── Application.java
│   │       ├── Handler.java
│   │       ├── service/
│   │       │   ├── UserService.java
│   │       │   └── DynamoDbUserService.java
│   │       └── repository/
│   │           └── UserRepository.java
│   └── resources/
│       ├── application.yml
│       └── logback.xml
└── test/
    └── java/
        └── com/example/
            └── HandlerTest.java
```

---

## Handler Implementation

### Basic API Gateway Handler

```java
package com.example;

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

public class Handler extends MicronautR