一、背景描绘
在项目中经过cat上报java对redis相关操作,从而监控redis指令操作的监控指标,在基础组件中写了如下装备:
@Configuration
@ConditionalOnClass({Cat.class,RedisOperations.class})
@Slf4j
public class CatRedisAutoConfiguration {
/**
* redis阻拦上报
*/
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
@ConditionalOnBean(RedisConnectionFactory.class)
@ConditionalOnMissingBean
public RedisAopService redisAopService(){
log.info("CatAutoConfiguration init RedisAopService...");
return new RedisAopService();
}
}
事务项目增加该装备后,发动项目发现RedisAopService并没有注入进去,redis相关操作并没有上报,怀疑是条件注解失效导致的问题。
二、常见条件注解失效场景
springboot中常见的条件注解有:
- @ConditionalOnClass:当类途径中存在指定的类时,条件才会建立。
- @ConditionalOnMissingClass:当类途径中不存在指定的类时,条件才会建立。
- @ConditionalOnBean:当容器中存在指定的 Bean 时,条件才会建立。
- @ConditionalOnMissingBean:当容器中不存在指定的 Bean 时,条件才会建立。
- @ConditionalOnProperty:当指定的特点在装备文件中被设置为特定的值时,条件才会建立。
- @ConditionalOnExpression:经过 SpEL 表达式来判别条件是否建立。
- @ConditionalOnWebApplication:当是一个 Web 应用程序时,条件才会建立。
- @ConditionalOnNotWebApplication:当不是一个 Web 应用程序时,条件才会建立。
这些条件注解也都是依据@Conditional完成,@Conditional 注解用于依据特定的条件来决议是否启用或禁用某个组件或装备。它能够应用于类、办法或装备类上。当条件不满意时,被 @Conditional 注解标记的组件或装备将被疏忽,不会被加载到 Spring 容器中。以下常见情况下,@Conditional注解或许会失效:
- 条件表达式始终回来 false:假如条件表达式的逻辑判别始终回来 false,那么被 @Conditional 注解标记的组件或装备将不会收效,无论条件是否满意。
- 条件依靠的Bean未被正确注入:在界说条件注解时,假如条件依靠某个 Bean 的存在或特点值,但这个 Bean 在运行时未被正确注入,那么条件判别或许会失效。
- 条件依靠的class未被加载:在条件注解依靠的class,未被引进或许因为版别抵触未被正确加载,也会导致条件注解失效。
- 条件不存在或装备过错:假如自界说的条件类或条件判别办法存在问题,或许装备了不存在的条件类,那么条件判别也或许失效。
- 条件不在正确的上下文中收效:有些条件注解只在特定的上下文环境下才会收效,例如 @ConditionalOnWebApplication 只在 Web 应用上下文中收效。假如将这样的条件注解应用在非对应的上下文环境中,条件判别也会失效。
- Bean注入次序问题:条件注解依靠的bean在条件注解收效判别时,还没有被注册成BeanDefination,但是终究会被注册进来,导致条件注解失效。
三、聊一聊条件注解完成原理
从之前的两篇文章《ConfigurationClassPostProcessor原理详解》和《springboot主动安装原理》中能够了解到装备类的解析和加载成BeanDefination都是由ConfigurationClassPostProcessor完成。 咱们选择@ConditionalOnBean为例,剖析一下springboot条件注解的视野原理,看一下@ConditionalOnBean完成:
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnBean {
Class<?>[] value() default {};
String[] type() default {};
Class<? extends Annotation>[] annotation() default {};
String[] name() default {};
SearchStrategy search() default SearchStrategy.ALL;
Class<?>[] parameterizedContainer() default {};
}
该注解依靠@Conditional注解,而且依靠OnBeanCondition.class,一般常用到的是value特点,也便是依靠的bean。 @ConditionalOnBean的收效依靠OnBeanCondition,看一下其承继联系 OnBeanCondition实质是是一个Condition,而且承继了SpringBootCondition具有一些条件注解的通用才能,而且具有其他一些东西才能。它的核心办法是完成SpringBootCondition界说的getMatchOutcome�办法,看一下办法完成:
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
ConditionMessage matchMessage = ConditionMessage.empty();
MergedAnnotations annotations = metadata.getAnnotations();
if (annotations.isPresent(ConditionalOnBean.class)) {
Spec<ConditionalOnBean> spec = new Spec<>(context, metadata, annotations, ConditionalOnBean.class);
MatchResult matchResult = getMatchingBeans(context, spec);
if (!matchResult.isAllMatched()) {
String reason = createOnBeanNoMatchReason(matchResult);
return ConditionOutcome.noMatch(spec.message().because(reason));
}
matchMessage = spec.message(matchMessage).found("bean", "beans").items(Style.QUOTE,
matchResult.getNamesOfAllMatches());
}
if (metadata.isAnnotated(ConditionalOnSingleCandidate.class.getName())) {
Spec<ConditionalOnSingleCandidate> spec = new SingleCandidateSpec(context, metadata, annotations);
MatchResult matchResult = getMatchingBeans(context, spec);
if (!matchResult.isAllMatched()) {
return ConditionOutcome.noMatch(spec.message().didNotFind("any beans").atAll());
}
else if (!hasSingleAutowireCandidate(context.getBeanFactory(), matchResult.getNamesOfAllMatches(),
spec.getStrategy() == SearchStrategy.ALL)) {
return ConditionOutcome.noMatch(spec.message().didNotFind("a primary bean from beans")
.items(Style.QUOTE, matchResult.getNamesOfAllMatches()));
}
matchMessage = spec.message(matchMessage).found("a primary bean from beans").items(Style.QUOTE,
matchResult.getNamesOfAllMatches());
}
if (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {
Spec<ConditionalOnMissingBean> spec = new Spec<>(context, metadata, annotations,
ConditionalOnMissingBean.class);
MatchResult matchResult = getMatchingBeans(context, spec);
if (matchResult.isAnyMatched()) {
String reason = createOnMissingBeanNoMatchReason(matchResult);
return ConditionOutcome.noMatch(spec.message().because(reason));
}
matchMessage = spec.message(matchMessage).didNotFind("any beans").atAll();
}
return ConditionOutcome.match(matchMessage);
}
该办法分别支撑@ConditionalOnBean、@ConditionalOnSingleCandidate和@ConditionalOnMissingBean三个条件注解的逻辑判定,持续剖析@ConditionalOnBean,便是查看容器中是否有契合条件的bean。会持续调用getMatchingBeans办法完成:
protected final MatchResult getMatchingBeans(ConditionContext context, Spec<?> spec) {
ClassLoader classLoader = context.getClassLoader();
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
boolean considerHierarchy = spec.getStrategy() != SearchStrategy.CURRENT;
Set<Class<?>> parameterizedContainers = spec.getParameterizedContainers();
if (spec.getStrategy() == SearchStrategy.ANCESTORS) {
BeanFactory parent = beanFactory.getParentBeanFactory();
Assert.isInstanceOf(ConfigurableListableBeanFactory.class, parent,
"Unable to use SearchStrategy.ANCESTORS");
beanFactory = (ConfigurableListableBeanFactory) parent;
}
MatchResult result = new MatchResult();
Set<String> beansIgnoredByType = getNamesOfBeansIgnoredByType(classLoader, beanFactory, considerHierarchy,
spec.getIgnoredTypes(), parameterizedContainers);
for (String type : spec.getTypes()) {
Collection<String> typeMatches = getBeanNamesForType(classLoader, considerHierarchy, beanFactory, type,
parameterizedContainers);
Iterator<String> iterator = typeMatches.iterator();
while (iterator.hasNext()) {
String match = iterator.next();
if (beansIgnoredByType.contains(match) || ScopedProxyUtils.isScopedTarget(match)) {
iterator.remove();
}
}
if (typeMatches.isEmpty()) {
result.recordUnmatchedType(type);
}
else {
result.recordMatchedType(type, typeMatches);
}
}
for (String annotation : spec.getAnnotations()) {
Set<String> annotationMatches = getBeanNamesForAnnotation(classLoader, beanFactory, annotation,
considerHierarchy);
annotationMatches.removeAll(beansIgnoredByType);
if (annotationMatches.isEmpty()) {
result.recordUnmatchedAnnotation(annotation);
}
else {
result.recordMatchedAnnotation(annotation, annotationMatches);
}
}
for (String beanName : spec.getNames()) {
if (!beansIgnoredByType.contains(beanName) && containsBean(beanFactory, beanName, considerHierarchy)) {
result.recordMatchedName(beanName);
}
else {
result.recordUnmatchedName(beanName);
}
}
return result;
}
此办法的逻辑是,从目标注解中解析出来value、type、name以及annotation特点,从beanFactory中查看是否存在契合条件的bean,而且在成果中标记是否匹配。 然后咱们再看一下springboot发动时,解析加载BeanDefination的逻辑,关于引导类的BeanDefination注册由ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry�办法完成:
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
int registryId = System.identityHashCode(registry);
if (this.registriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
}
if (this.factoriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + registry);
}
this.registriesPostProcessed.add(registryId);
processConfigBeanDefinitions(registry);
}
在经过ConfigurationClassParser�类解析后,会经过ConfigurationClassBeanDefinitionReader�类的loadBeanDefinitions�办法加载:
public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
for (ConfigurationClass configClass : configurationModel) {
loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
}
}
此处创建了TrackedConditionEvaluator类型的ConditionEvaluator,持有ConditionEvaluator实例,然后调用loadBeanDefinitionsForConfigurationClass办法加载@Configuration注解类。
private void loadBeanDefinitionsForConfigurationClass(
ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
if (trackedConditionEvaluator.shouldSkip(configClass)) {
String beanName = configClass.getBeanName();
if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
this.registry.removeBeanDefinition(beanName);
}
this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
return;
}
if (configClass.isImported()) {
registerBeanDefinitionForImportedConfigurationClass(configClass);
}
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
loadBeanDefinitionsForBeanMethod(beanMethod);
}
//省掉...
}
该办法先查看外层@Configuration注解的类是否需求越过加载,假如越过就不加载,假如不越过就持续解析加载里面的内容,TrackedConditionEvaluator的shouldSkip逻辑会委托给ConditionEvaluator�处理,此处暂不展开剖析,在@Configuration类里面@Bean和@ConditionalOnBean注解的办法解析时一起剖析。咱们在@Configuration注解的类里面界说了@Bean注解办法注册bean,然后遍历并调用loadBeanDefinitionsForBeanMethod办法加载注册BeanDefination,看一下完成:
private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
ConfigurationClass configClass = beanMethod.getConfigurationClass();
MethodMetadata metadata = beanMethod.getMetadata();
String methodName = metadata.getMethodName();
// Do we need to mark the bean as skipped by its condition?
if (this.conditionEvaluator.shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN)) {
configClass.skippedBeanMethods.add(methodName);
return;
}
if (configClass.skippedBeanMethods.contains(methodName)) {
return;
}
AnnotationAttributes bean = AnnotationConfigUtils.attributesFor(metadata, Bean.class);
Assert.state(bean != null, "No @Bean annotation attributes");
//省掉...
this.registry.registerBeanDefinition(beanName, beanDefToRegister);
}
上述办法省掉掉了中心组装需求注册的bean的BeanDefination相关内容,全体逻辑大概是,先查看是否需求越过注册,假如越过则直接回来,不注册BeanDefination,否则组装BeanDefination并注册到容器中。咱们主要看一下conditionEvaluator.shouldSkip的完成:
public boolean shouldSkip(@Nullable AnnotatedTypeMetadata metadata, @Nullable ConfigurationPhase phase) {
if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
return false;
}
if (phase == null) {
if (metadata instanceof AnnotationMetadata &&
ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
}
return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
}
List<Condition> conditions = new ArrayList<>();
for (String[] conditionClasses : getConditionClasses(metadata)) {
for (String conditionClass : conditionClasses) {
Condition condition = getCondition(conditionClass, this.context.getClassLoader());
conditions.add(condition);
}
}
AnnotationAwareOrderComparator.sort(conditions);
for (Condition condition : conditions) {
ConfigurationPhase requiredPhase = null;
if (condition instanceof ConfigurationCondition) {
requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
}
if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) {
return true;
}
}
return false;
}
该办法做了以下工作:
- 假如元数据为空,或许没有被@Conditional注解,则回来false,不越过注册@Bean
- 假如装备阶段为空,则重新提取调用,否则装备阶段默以为REGISTER_BEAN
- 从元数据解析出来@Conditional中的依靠类,比方@ConditionalOnBean运用@Conditional(OnBeanCondition.class),那么此处提取出来的Condition类便是OnBeanCondition
- 实例化Condition类并增加到conditions备用,之所以这里是列表,是因为或许@Bean标注的办法上除了@ConditionalOnBean还有@ConditionalOnMissingBean等多个条件注解
- 对条件注解支撑类Condition列表进行排序,然后遍历判别是否满意一切条件,假如是回来正常注册,否则越过注册
这里的关键点是condition.matches办法,前边咱们运用的是@ConditionalOnBean,所以此处的Condition是OnBeanCondition,咱们看一下它的matches办法完成,前边从承继联系中看到OnBeanCondition承继了SpringBootCondition�,matches办法的界说和完成在SpringBootCondition中:
public final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
String classOrMethodName = getClassOrMethodName(metadata);
try {
ConditionOutcome outcome = getMatchOutcome(context, metadata);
logOutcome(classOrMethodName, outcome);
recordEvaluation(context, classOrMethodName, outcome);
return outcome.isMatch();
}
catch (NoClassDefFoundError ex) {
throw new IllegalStateException(ex);
}
catch (RuntimeException ex) {
throw new IllegalStateException("Error processing condition on " + getName(metadata), ex);
}
}
此办法调用getMatchOutcome办法,并经过回来成果的isMatch决议是否找到匹配,该类的getMatchOutcome办法是抽象,交给子类完成,这里便是咱们前边剖析的OnBeanCondition类的getMatchOutcome办法。 因为咱们先剖析的OnBeanCondition,后剖析的条件注解调用,不太好了解,梳理了一下,全体流程大致如下: 另外一些依据@Conditional完成的条件注解,运行原理也根本类似,区别在于其依托的完成类不同:
- @ConditionalOnBean->OnBeanCondition
- @ConditionalOnClass -> OnClassCondition�
- @ConditionalOnProperty -> OnPropertyCondition�
- @ConditionalOnExpression -> OnExpressionCondition�
- @ConditionalOnWebApplication -> OnWebApplicationCondition�
四、问题定位
从前边的剖析中,咱们了解了条件注解工作原理,以及失效的常见原因,结合篇头装备代码,发现咱们写的装备类是@Configuration注解的普通引导类,而依靠的bean是经过starter注入进来的主动安装类,经过代码debug,能够看到: 此段代码方位是ConfigurationClassPostProcessor�的processConfigBeanDefinitions�办法,解析到的装备类次序是,@Configuration注解的普通装备类优先于主动安装类,BeanDefination注册次序也是依照这个次序,那么也就呈现了,咱们前边条件注解失效,导致@Bean对应的Bean没有注册进来,原因便是执行普通@Configuration注解标注类以及内部@Bean的时分,执行条件注解逻辑,从容器中没有找到@ConditionalOnBean依靠类的BeanDefination界说,所以就呈现目标类没有正常注入的问题。
五、解决方案
想要解决上述问题,要保证装备类的解析和加载在依靠类之后,也便是运用@ConditionalOnBean注解的类的条件判定和注册必须要在依靠的类之后,能够参阅一下方案。
1.确保主动安装类的优先级高于装备类
在主动安装类上运用 @AutoConfigureBefore 或 @AutoConfigureAfter 注解,显式指定主动安装类的加载次序。确保主动安装类在装备类之前被加载和处理。
@AutoConfigureBefore(CatAutoConfiguration.class)
@Configuration
public class SomeAutoConfiguration {
// ...
}
2.将@Bean办法移动到主动安装类中
将有 @ConditionalOnBean 注解的 @Bean 办法移到主动安装类中,这样就能够保证主动安装类中的 Bean 先被加载和注册,满意 @ConditionalOnBean 的条件要求。
@Configuration
public class CatAutoConfiguration {
// ...
}
@Configuration
@ConditionalOnClass({Cat.class})
@Slf4j
public class SomeAutoConfiguration {
@Bean
@ConditionalOnBean(RedisConnectionFactory.class)
public RedisAopService redisAopService() {
// ...
}
}
3.运用@DependsOn注解
在需求等候主动安装类中某个 Bean 加载结束后再初始化 @Bean 的情况下,能够在 @Bean 办法上运用 @DependsOn 注解,指定依靠的 Bean 的名称。
@Configuration
public class CatAutoConfiguration {
@Bean
public RedisConnectionFactory redisConnectionFactory() {
// ...
}
}
@Configuration
@ConditionalOnClass({Cat.class})
@Slf4j
public class SomeAutoConfiguration {
@Bean
@ConditionalOnBean(name = "redisConnectionFactory")
@DependsOn("redisConnectionFactory") // 等候 redisConnectionFactory 初始化结束
public RedisAopService redisAopService() {
// ...
}
}
六、参阅
view.inews.qq.com/k/20220709A… blog.csdn.net/qq_41737716… dmsupine.com/2021/04/27/… mp.weixin.qq.com/s/IA8P03Klz…