Exploring Spring Framework 6.0’s New GraalVM AOT Support and Configuration

In the previous article "Spring 6.0 Changes | Spring Boot 3.0 Preview" we introduced some Spring updates. Beyond a few dependency adjustments, today we dive into the most significant change: the new GraalVM AOT support.

1. Spring core

Spring Framework 6.0 adds major changes to Spring core, introducing the following packages:

GraalVM feature – allows client‑side interception of native image generation and execution of custom initialization code at different stages (the GraalVM API may change and is not part of the public framework API).

aot – the core package for Spring AOT infrastructure.

javapoet – a Java API for generating Java source code.

The

javapoet

package contains only one file,

package-info.java

, which is the repackaged Square open‑source JavaPoet library.

<code>/**
 * Spring's repackaging of
 * <a href="https://github.com/square/javapoet">JavaPoet</a>
 * (with Spring‑specific utilities; for internal use only).
 */
package org.springframework.javapoet;
</code>

After compilation, the GraalVM feature module is also packaged under

aot/graalvm

. Additional resources include the new

aot.factories

file.

2. Spring beans

Support for GraalVM AOT is added to Spring bean factories, which also introduces the aot.factories file.

3. Spring context

Application context AOT support is added.

4. Other modules

The three modules above add AOT extension interfaces; other Spring Framework modules only need to define an aot.factories file. Below is an example of such a file (located at spring-web/src/main/resources/META-INF/spring/aot.factories ):

<code>org.springframework.aot.hint.RuntimeHintsRegistrar= \
org.springframework.http.HttpMimeTypesRuntimeHints,\
org.springframework.http.codec.CodecConfigurerRuntimeHints,\
org.springframework.http.converter.json.JacksonModulesRuntimeHints,\
org.springframework.web.util.WebUtilRuntimeHints
</code>

The HttpMimeTypesRuntimeHints class registers the mime.types resource file.

<code>class HttpMimeTypesRuntimeHints implements RuntimeHintsRegistrar {
    @Override
    public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
        hints.resources().registerPattern("org/springframework/http/mime.types");
    }
}
</code>

The CodecConfigurerRuntimeHints class registers the CodecConfigurer.properties file and related classes.

<code>class CodecConfigurerRuntimeHints implements RuntimeHintsRegistrar {
    @Override
    public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
        hints.resources().registerPattern(
            "org/springframework/http/codec/CodecConfigurer.properties");
        hints.reflection().registerTypes(
            TypeReference.listOf(DefaultClientCodecConfigurer.class, DefaultServerCodecConfigurer.class),
            typeHint -> typeHint.onReachableType(CodecConfigurerFactory.class)
                .withMembers(MemberCategory.INVOKE_PUBLIC_CONSTRUCTORS));
    }
}
</code>

The CodecConfigurer.properties file content:

<code># Default CodecConfigurer implementation classes for static Client/ServerCodecConfigurer.create() calls.
# Not meant to be customized by application developers; simply instantiate custom impl classes instead.

org.springframework.http.codec.ClientCodecConfigurer=org.springframework.http.codec.support.DefaultClientCodecConfigurer
org.springframework.http.codec.ServerCodecConfigurer=org.springframework.http.codec.support.DefaultServerCodecConfigurer
</code>

5. Summary

Spring Framework 6.0 adds GraalVM AOT support extensions and the aot.factories configuration file/specification, enabling developers to extend support for dependencies that do not natively work with GraalVM AOT (e.g., custom resources, reflection) by configuring the aot.factories file. Before Spring Boot 3.0, GraalVM AOT required the spring-native dependency to extend support for resources, reflection, etc. After Spring Boot 3.0 / Spring Framework 6.0, the built‑in support can be used directly by customizing the aot.factories file. In the future, mica-auto will also support generating aot.factories files via annotations.