Quarkus是否有类似@ConditionalOnBean的注解或方法？扩展开发咨询

核心思路 #

在Quarkus构建阶段的BuildStep中，通过CombinedIndexBuildItem获取全应用的类元数据索引，检查用户自定义的BeanA是否存在且被标记为合法CDI Bean，以此决定是否注册BeanB。

你之前代码的问题 #

用getKnownUsers()是找哪些类用到了BeanA（比如把BeanA当字段、参数的类），不是判断BeanA本身是不是被定义成了CDI Bean，所以逻辑不对。

正确实现代码 #

import io.quarkus.deployment.annotations.BuildStep;
import io.quarkus.deployment.builditem.CombinedIndexBuildItem;
import io.quarkus.deployment.builditem.AdditionalBeanBuildItem;
import org.jboss.jandex.ClassInfo;
import org.jboss.jandex.DotName;

@BuildStep
void registerBeanProducers(CombinedIndexBuildItem combinedIndex,
                           BuildProducer<AdditionalBeanBuildItem> additionalBeans) {
    // 拿到BeanA的类名对应的DotName
    DotName beanADotName = DotName.createSimple(BeanA.class.getName());
    ClassInfo beanAClassInfo = combinedIndex.getIndex().getClassByName(beanADotName);

    if (beanAClassInfo != null) {
        // 检查这个类是否带CDI作用域注解（比如@ApplicationScoped、@Singleton）
        boolean isCdiBean = beanAClassInfo.annotations().stream()
                .anyMatch(anno -> {
                    DotName annoName = anno.name();
                    // 匹配Jakarta EE的CDI作用域
                    return annoName.startsWith("jakarta.enterprise.context.")
                            // 兼容旧版Java EE注解
                            || annoName.startsWith("javax.enterprise.context.")
                            // 如果要支持Spring风格的Bean，加这个判断
                            || annoName.equals(DotName.createSimple("org.springframework.stereotype.Component"));
                });

        if (isCdiBean) {
            // 注册不可移除的BeanB
            AdditionalBeanBuildItem beanBItem = AdditionalBeanBuildItem.builder()
                    .setUnremovable()
                    .addBeanClass(BeanB.class)
                    .build();
            additionalBeans.produce(beanBItem);
        }
    }
}

更精准的Bean判断（进阶） #

如果要严格按照Quarkus的CDI规则判断BeanA是否会被识别为Bean，可以用Arc的BeanProcessor：

import io.quarkus.arc.processor.BeanInfo;
import io.quarkus.deployment.annotations.BuildStep;
import io.quarkus.deployment.builditem.CombinedIndexBuildItem;
import io.quarkus.deployment.builditem.AdditionalBeanBuildItem;
import io.quarkus.deployment.builditem.BeanProcessorBuildItem;
import org.jboss.jandex.ClassInfo;
import org.jboss.jandex.DotName;

@BuildStep
void registerBeanProducers(CombinedIndexBuildItem combinedIndex,
                           BeanProcessorBuildItem beanProcessorItem,
                           BuildProducer<AdditionalBeanBuildItem> additionalBeans) {
    DotName beanADotName = DotName.createSimple(BeanA.class.getName());
    ClassInfo beanAClassInfo = combinedIndex.getIndex().getClassByName(beanADotName);

    if (beanAClassInfo != null) {
        // 用Arc的BeanProcessor分析类是否为合法Bean
        BeanInfo beanInfo = beanProcessorItem.getBeanProcessor().buildBeanInfo(beanAClassInfo, combinedIndex.getIndex());
        if (beanInfo != null && beanInfo.isBean()) {
            // 注册BeanB
            AdditionalBeanBuildItem beanBItem = AdditionalBeanBuildItem.builder()
                    .setUnremovable()
                    .addBeanClass(BeanB.class)
                    .build();
            additionalBeans.produce(beanBItem);
        }
    }
}

内容的提问来源于stack exchange，提问作者Hydra