Spring-Boot @ConditionalOnMissingBean 具有多种类型的泛型类

问题描述 投票：0回答：1

问题

在我们的 Spring-Boot-Stater 项目（Spring-Boot 3.2.3）中，我们有一个默认的 Converter Bean。为了简单起见，我们可以说它将整数转换为字符串。由于这是一个很好的实践，我们用 @ConditionalOnMissingBean 注释 Bean。 Bean 已正确初始化，并且可以更换为另一个实现，不会出现任何问题。 但是，如果我们为其他类型（即 Foo 到 Baa）创建 Converter Bean，则不会创建默认 bean，并且当我们尝试注入它时，我们会收到 UnsatisfiedDependencyException。

当使用 Spring Boot @ConditionalOnMissingBean 和泛型类型中提到的类型信息更新 @ConditionalOnMissingBean 时，应用程序不再以 IllegalStateException 启动。

示例

spring-boot-starter 中的默认转换器

@Bean
@ConditionalOnMissingBean(parameterizedContainer = Converter.class, value={Integer.class, String.class})
public Converter<Integer,String> exampleConverter() {
    return Integer::toHexString;
}

更换转换器

@Bean
Converter<Integer, String> exampleConverter() {
    return Integer::toBinaryString;
}

项目中的一些其他转换器

@Bean
Converter<String, String> uppercaseConverter() {
    return String::toUpperCase;
}

解决方法

我们当前使用的不理想的选项是通过名称限制 bean。

@Bean
@ConditionalOnMissingBean(name = "exampleConverter")
public Converter<Integer,String> exampleConverter() {
    return Integer::toHexString;
}

问题

因此，我们找到了一种解决方法，但这并不理想。实际的问题是，我是否在通用条件上做错了什么，或者这是 Spring-Boot 中的一个 Bug，我应该在 GitHub 上提交一个问题？

错误日志

java.lang.IllegalStateException: Error processing condition on io.d4e.starter.ExampleAutoConfiguration.exampleConverter
    at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:60) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:108) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod(ConfigurationClassBeanDefinitionReader.java:183) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForConfigurationClass(ConfigurationClassBeanDefinitionReader.java:144) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitions(ConfigurationClassBeanDefinitionReader.java:120) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:428) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:289) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:349) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:118) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:788) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:606) ~[spring-context-6.1.4.jar:6.1.4]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-3.2.3.jar:3.2.3]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:456) ~[spring-boot-3.2.3.jar:3.2.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:334) ~[spring-boot-3.2.3.jar:3.2.3]
    at org.springframework.boot.test.context.SpringBootContextLoader.lambda$loadContext$3(SpringBootContextLoader.java:137) ~[spring-boot-test-3.2.3.jar:3.2.3]
    at org.springframework.util.function.ThrowingSupplier.get(ThrowingSupplier.java:58) ~[spring-core-6.1.4.jar:6.1.4]
    at org.springframework.util.function.ThrowingSupplier.get(ThrowingSupplier.java:46) ~[spring-core-6.1.4.jar:6.1.4]
    at org.springframework.boot.SpringApplication.withHook(SpringApplication.java:1454) ~[spring-boot-3.2.3.jar:3.2.3]
    at org.springframework.boot.test.context.SpringBootContextLoader$ContextLoaderHook.run(SpringBootContextLoader.java:553) ~[spring-boot-test-3.2.3.jar:3.2.3]
    at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:137) ~[spring-boot-test-3.2.3.jar:3.2.3]
    at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:108) ~[spring-boot-test-3.2.3.jar:3.2.3]
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:225) ~[spring-test-6.1.4.jar:6.1.4]
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:152) ~[spring-test-6.1.4.jar:6.1.4]
    at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:130) ~[spring-test-6.1.4.jar:6.1.4]
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:142) ~[spring-test-6.1.4.jar:6.1.4]
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:98) ~[spring-test-6.1.4.jar:6.1.4]
    at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:260) ~[spring-test-6.1.4.jar:6.1.4]
    at org.springframework.test.context.junit.jupiter.SpringExtension.postProcessTestInstance(SpringExtension.java:163) ~[spring-test-6.1.4.jar:6.1.4]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeTestInstancePostProcessors$10(ClassBasedTestDescriptor.java:378) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.executeAndMaskThrowable(ClassBasedTestDescriptor.java:383) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeTestInstancePostProcessors$11(ClassBasedTestDescriptor.java:378) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~[na:na]
    at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179) ~[na:na]
    at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~[na:na]
    at java.base/java.util.stream.StreamSpliterators$WrappingSpliterator.forEachRemaining(StreamSpliterators.java:310) ~[na:na]
    at java.base/java.util.stream.Streams$ConcatSpliterator.forEachRemaining(Streams.java:735) ~[na:na]
    at java.base/java.util.stream.Streams$ConcatSpliterator.forEachRemaining(Streams.java:734) ~[na:na]
    at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[na:na]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.invokeTestInstancePostProcessors(ClassBasedTestDescriptor.java:377) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$instantiateAndPostProcessTestInstance$6(ClassBasedTestDescriptor.java:290) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.instantiateAndPostProcessTestInstance(ClassBasedTestDescriptor.java:289) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$testInstancesProvider$4(ClassBasedTestDescriptor.java:279) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at java.base/java.util.Optional.orElseGet(Optional.java:364) ~[na:na]
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$testInstancesProvider$5(ClassBasedTestDescriptor.java:278) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.execution.TestInstancesProvider.getTestInstances(TestInstancesProvider.java:31) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$prepare$0(TestMethodTestDescriptor.java:106) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.prepare(TestMethodTestDescriptor.java:105) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.prepare(TestMethodTestDescriptor.java:69) ~[junit-jupiter-engine-5.10.2.jar:5.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$prepare$2(NodeTestTask.java:123) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.prepare(NodeTestTask.java:123) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:90) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) ~[na:na]
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) ~[na:na]
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54) ~[junit-platform-engine-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:198) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:169) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:93) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:58) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:141) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:57) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:103) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:85) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:63) ~[junit-platform-launcher-1.10.2.jar:1.10.2]
    at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:57) ~[junit5-rt.jar:na]
    at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38) ~[junit-rt.jar:na]
    at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11) ~[idea_rt.jar:na]
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35) ~[junit-rt.jar:na]
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232) ~[junit-rt.jar:na]
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55) ~[junit-rt.jar:na]
Caused by: java.lang.IllegalArgumentException: Mismatched number of generics specified for public abstract interface org.springframework.core.convert.converter.Converter<S,T>
    at org.springframework.util.Assert.isTrue(Assert.java:129) ~[spring-core-6.1.4.jar:6.1.4]
    at org.springframework.core.ResolvableType.forClassWithGenerics(ResolvableType.java:1125) ~[spring-core-6.1.4.jar:6.1.4]
    at org.springframework.core.ResolvableType.forClassWithGenerics(ResolvableType.java:1111) ~[spring-core-6.1.4.jar:6.1.4]
    at org.springframework.boot.autoconfigure.condition.OnBeanCondition.collectBeanNamesForType(OnBeanCondition.java:249) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getBeanNamesForType(OnBeanCondition.java:240) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getBeanNamesForType(OnBeanCondition.java:230) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getMatchingBeans(OnBeanCondition.java:183) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    at org.springframework.boot.autoconfigure.condition.OnBeanCondition.getMatchOutcome(OnBeanCondition.java:158) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:47) ~[spring-boot-autoconfigure-3.2.3.jar:3.2.3]
    ... 94 common frames omitted
spring spring-boot generics
1个回答
0
投票

我是否在通用条件上做错了什么，或者这是 Spring-Boot 中的一个 Bug，我应该在 GitHub 上提交一个问题？

这绝对不是一个错误。恐怕您稍微误解了 

value
注释中的 
@ConditionalOnMissingBean
参数。向 
value
参数添加多个类的功能用于为给定 Bean 类型的存在添加多个条件。

例如，创建这样的注释：

@ConditionalOnMissingBean(parameterizedContainer = Converter.class, value={Integer.class, String.class})

Spring 的理解是：“如果既没有 

Converter<Integer>
类型的 Bean，也没有 
Converser<String>
类型的 Bean，则创建一个 Bean”。

创建 

parameterizedContainer
参数是为了定义仅具有一种泛型类型的泛型 Bean。恐怕没有开箱即用的解决方案来实现您想要实现的目标，唯一的解决方案是使用您在问题中链接的 Stack Overflow 线程中的 
org.springframework.context.annotation.Condition
。

来源：https://github.com/spring-projects/spring-boot/issues/27410#issuecomment-899711749

添加parameterizedContainer属性主要是为了支持像ServletRegistrationBean bean这样的类。我们的想法是检测特定类型的 bean 或其包装器。例如，MyServlet 或 ServletRegistrationBean 都将匹配 @ConditionalOnBean(value=MyServlet.class,parameterizedContainer=ServletRegistrationBean.class)。 看起来你正在尝试做一些稍微不同的事情。我猜您只想在缺少 Converter bean 的情况下注册 PersonToPepUserConverter 。恐怕没有现成的条件注释可以做到这一点。您也许可以编写自己的条件，使用不同的 ResolvableType 调用 beanFactory.getBeanNamesForType。 (...)

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