Spring Boot类不可见ByteBuddy@Entity注释PathBeanDefinitionScanner basePackages扫描

Question

     public Set<BeanDefinition> findCandidateComponents(String basePackage) {
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

        Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);

        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

        MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);

        if (isCandidateComponent(metadataReader)) {

        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ClassLoader cl = getClassLoader();
    Enumeration<URL> resourceUrls = (cl != null ? cl.getResources(path) : ClassLoader.getSystemResources(path));

MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);

上面的getMetadataReader方法调用最终以

final class SimpleMetadataReader implements MetadataReader 

它使用ASM ClassReader访问类和注释元数据。这显然找不到ByteBuddy放置的@Entity注释。

我不确定我是否应该以某种方式将Classloader链接到Bytebuddy中，或者重写Springs SimpleMetadataReader，以使我自己的实现得到Bytebuddy的支持。

public static void main(String[] args) {
    EntityAgent.install(ByteBuddyAgent.install());
    InversionContainer.startInversion(args);
}

**
* Transform all Non-Abstract Classes which extend BaseEntity
* to have the annotation Entity
*/
public class EntityAgent {

    /**
     * Installs the agent builder to the instrumentation API.
     */
    public static void install(Instrumentation inst) {
        createAgentBuilder().installOn(inst);
    }

    /**
      * Creates the AgentBuilder that will redefine any class extending BaseEntity
     */
    private static AgentBuilder createAgentBuilder() {
        return new AgentBuilder.Default()
                .with(toSystemError())
                .with(AgentBuilder.RedefinitionStrategy.REDEFINITION)
                .with(AgentBuilder.InitializationStrategy.SelfInjection.EAGER)
                .with(AgentBuilder.TypeStrategy.Default.REDEFINE)
                .type(getClassMatcher())
                .transform(getTransformer());
    }

    /**
     * Set Entity annotation on Class
     */
    private static AgentBuilder.Transformer getTransformer() {
        return (builder, typeDescription, classloader) -> builder.annotateType(AnnotationDescription.Builder.ofType(Entity.class).build());
    }

    /**
     * Find any non-abstract class that extends BaseEntity
     */
    private static ElementMatcher.Junction<TypeDescription> get ClassMatcher() {
        return ElementMatchers.isSubTypeOf(BaseEntity.class).and(ElementMatchers.not(ElementMatchers.isAbstract()));
    }
}

让我知道如果你想要更多的实现细节。我想把bytebuddy和spring集成起来，这样我就可以用spring组件注释来测试类。

Answer 1

“问题”在于Spring只关注原始类，而不是加载的类。Byte Buddy注册一个Java代理，该代理在加载类时转换类，但保留Spring Boot无法识别的原始类文件。

另一个问题是Spring在启动时和加载类之前会调查jar文件。这意味着当Spring收集其实体时，Byte Buddy代理甚至还没有活动。

相反，Spring应该调查加载的类，因为类加载器可能甚至不提供类文件，但我假设它们试图保留导致这种结果的类加载顺序。