Spring Boot组件扫描不起作用

Question

I have created a sample Spring Boot application that runs perfectly fine when service classes are all in one package , but if a Service class refers to another service class in a different package then I get the BeanCreationException

The Code for the Application is given below

Main.java

 @SpringBootApplication
public class Main {

    public static void main(String[] args) {
        SpringApplication.run(Main.class, args);

    }
}

MyRunner

@Component
@ComponentScan(basePackages ="com.springboot.helloworld")
public class MyRunner implements CommandLineRunner {

    @Autowired
    private GreeterService greeterService;

    @Override
    public void run(String... args) throws Exception {
        System.out.println(greeterService.greetGuest("John Doe"));
    }
}

GreeterService and GreeterServiceImpl are in com.springboot.helloworld.Greeter

@Service
public class GreeterServiceImpl implements GreeterService {

    @Autowired
    Sample service;
    @Override
    public String greetGuest(String greeter) {

        if (greeter == null) {
            return "Looged in as Guest";
        }

        return "Hello " + greeter + " How are you?";
    }

}

Sample and SampleImpl are in different Package com.springboot.helloworld.Sampler

Error Recieved is

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'greeterServiceImpl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.springboot.helloworld.Sampler.Sample com.springboot.helloworld.Greeter.GreeterServiceImpl.service; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.springboot.helloworld.Sampler.Sample] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1210)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:686)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:320)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:957)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:946)
    at com.springboot.helloworld.Main.main(Main.java:10)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.springboot.helloworld.Sampler.Sample com.springboot.helloworld.Greeter.GreeterServiceImpl.service; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.springboot.helloworld.Sampler.Sample] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 15 common frames omitted
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.springboot.helloworld.Sampler.Sample] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
    ... 17 common frames omitted

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'greeterServiceImpl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.springboot.helloworld.Sampler.Sample com.springboot.helloworld.Greeter.GreeterServiceImpl.service; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.springboot.helloworld.Sampler.Sample] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1210)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:686)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:320)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:957)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:946)
    at com.springboot.helloworld.Main.main(Main.java:10)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.springboot.helloworld.Sampler.Sample com.springboot.helloworld.Greeter.GreeterServiceImpl.service; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.springboot.helloworld.Sampler.Sample] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 15 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.springboot.helloworld.Sampler.Sample] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
    ... 17 more

Answer 1

您必须使用@Component注释，如下所示：

@ComponentScan({"com.springboot.helloworld","service"})

Answer 2

您的应用程序显然期望命令行参数，并且您不提供任何参数。

Answer 3

I had this issue after switching to spring 5. The problem was that an annotation processor was being run at build time to generate some helper classes, a side effect of this was that a file, spring.properties was generated. This got deployed to META-INF. When spring 5 scans for components, it checks to see if this file exists (as a resource loaded by the class loader), if it exists then it only considers the classes listed in the file when looking for components. In my case the annotation processor that generated the file wasn't looking for components, so the component classes weren't in the file. The fix was to delete the file. Without the file, then the component scanning works as expected.