graalvm-native-image

# GraalVM Native Image for Java Applications

Expert skill for building high-performance native executables from Java applications using GraalVM Native Image, dramatically reducing startup time and memory consumption.

## Overview

GraalVM Native Image compiles Java applications ahead-of-time (AOT) into standalone native executables. These executables start in milliseconds, require significantly less memory than JVM-based deployments, and are ideal for serverless functions, CLI tools, and microservices where fast startup and low resource usage are critical.

This skill provides a structured workflow to migrate JVM applications to native binaries, covering build tool configuration, framework-specific patterns, reflection metadata management, and an iterative approach to resolving native build failures.

## When to Use

Use this skill when:
- Converting a JVM-based Java application to a GraalVM native executable
- Optimizing cold start times for serverless or containerized deployments
- Reducing memory footprint (RSS) of Java microservices
- Configuring Maven or Gradle with GraalVM Native Build Tools
- Resolving `ClassNotFoundException`, `NoSuchMethodException`, or missing resource errors in native builds
- Generating or editing `reflect-config.json`, `resource-config.json`, or other GraalVM metadata files
- Using the GraalVM tracing agent to collect reachability metadata
- Implementing `RuntimeHints` for Spring Boot native support
- Building native images with Quarkus or Micronaut

## Instructions

### 1. Contextual Project Analysis

Before any configuration, analyze the project to determine the build tool, framework, and dependencies:

**Detect the build tool:**

```bash
# Check for Maven
if [ -f "pom.xml" ]; then
    echo "Build tool: Maven"
    # Check for Maven wrapper
    [ -f "mvnw" ] && echo "Maven wrapper available"
fi

# Check for Gradle
if [ -f "build.gradle" ] || [ -f "build.gradle.kts" ]; then
    echo "Build tool: Gradle"
    [ -f "build.gradle.kts" ] && echo "Kotlin DSL"
    [ -f "gradlew" ] && echo "Gradle wrapper available"
fi
```

**Detect the framework by analyzing dependencies:**

- **Spring Boot**: Look for `spring-boot-starter-*` in `pom.xml` or `build.gradle`
- **Quarkus**: Look for `quarkus-*` dependencies
- **Micronaut**: Look for `micronaut-*` dependencies
- **Plain Java**: No framework dependencies detected

**Check the Java version:**

```bash
java -version 2>&1
# GraalVM Native Image requires Java 17+ (recommended: Java 21+)
```

**Identify potential native image challenges:**

- Reflection-heavy libraries (Jackson, Hibernate, JAXB)
- Dynamic proxy usage (JDK proxies, CGLIB)
- Resource bundles and classpath resources
- JNI or native library dependencies
- Serialization requirements

### 2. Build Tool Configuration

Configure the appropriate build tool plugin based on the detected environment.

**For Maven projects**, add a dedicated `native` profile to keep the standard build clean. See the [Maven Native Profile Reference](references/maven-native-profile.md) for full configuration.

Key Maven setup:

```xml
<profiles>
  <profile>
    <id>native</id>
    <build>
      <plugins>
        <plugin>
          <groupId>org.graalvm.buildtools</groupId>
          <artifactId>native-maven-plugin</artifactId>
          <version>0.10.6</version>
          <extensions>true</extensions>
          <executions>
            <execution>
              <id>build-native</id>
              <goals>
                <goal>compile-no-fork</goal>
              </goals>
              <phase>package</phase>
            </execution>
          </executions>
          <configuration>
            <imageName>${project.artifactId}</imageName>
            <buildArgs>
              <buildArg>--no-fallback</buildArg>
            </buildArgs>
          </configuration>
        </plugin>
      </plugins>
    </build>
  </profile>
</profiles>
```

Build with: `./mvnw -Pnative package`

**For Gradle projects**, apply the `org.graalvm.buildtools.native` plugin. See the [Gradle Native Plugin Reference](references/gradle-native-plugin.md) for full configuration.

Key Gradle setup (Kotlin DSL):

```kotlin
plugins {
    id("org.graalvm.buildtools.native") version "0.10.6"
}

graalvmNative {
    binaries {
        named("main") {
            imageName.set(project.name)
            buildArgs.add("--no-fallback")
        }
    }
}
```

Build with: `./gradlew nativeCompile`

### 3. Framework-Specific Configuration

Each framework has its own AOT strategy. Apply the correct configuration based on the detected framework.

**Spring Boot** (3.x+): Spring Boot has built-in GraalVM support with AOT processing. See the [Spring Boot Native Reference](references/spring-boot-native.md) for patterns including `RuntimeHints`, `@RegisterReflectionForBinding`, and test support.

Key points:
- Use `spring-boot-starter-parent` 3.x+ which includes the native profile
- Register reflection hints via `RuntimeHintsRegistrar`
- Run AOT processing with `process-aot` goal
- Build with: `./mvnw -Pnative native:compile` or `./gradlew nativeCompile`

**Quarkus and Micronaut**: These frameworks are designed native-first and require minimal additional configuration. See the [Quarkus & Micronaut Reference](references/quarkus-micronaut-native.md).

### 4. GraalVM Reachability Metadata

Native Image uses a closed-world assumption — all code paths must be known at build time. Dynamic features like reflection, resources, and proxies require explicit metadata configuration.

**Metadata files** are placed in `META-INF/native-image/<group.id>/<artifact.id>/`:

| File | Purpose |
|------|---------|
| `reachability-metadata.json` | Unified metadata (reflection, resources, JNI, proxies, bundles, serialization) |
| `reflect-config.json` | Legacy: Reflection registration |
| `resource-config.json` | Legacy: Resource inclusion patterns |
| `proxy-config.json` | Legacy: Dynamic proxy interfaces |
| `serialization-config.json` | Legacy: Serialization reg