Why does ProxyFactoryBean throw "No qualifying bean of type" with @Autowired? And doesn&#0-CodePudding

I've tried to use ProxyFactoryBean with @Autowired, but it throws an exception at the setInstrument method.

The question - why does it work with previously called getBean method or @DependsOn? I'm trying to understand what Spring performs for these additional steps.

Thank you in advance!

I have two interfaces - Singer and Instrument. And two implementations for them - GuitarSinger.class and Guitar.class.

Singer.class:

public interface Singer {
    void singSong();
    Instrument getInstrument();
}

GuitarSinger.class (Singer implementation):

@Service
@Lazy
public class GuitarSinger implements Singer {

    private Instrument guitar;

    @Autowired
    public void setInstrument(Instrument instrument) {
        this.guitar = instrument;
    }

    @Override
    public Instrument getInstrument() {
        return guitar;
    }

    @Override
    public void singSong() {
        System.out.println("I'm singing a song");
        guitar.play();
    }
}

Instrument.class interface:

public interface Instrument {
    void play();
}

and Guitar.class (Instrument.class interface implementation):

public class Guitar implements Instrument {
    @Override
    public void play() {
        System.out.println("I'm a guitar!");
    }
}

And one interface for proxy introduction - GuitarChecker.class:

public interface GuitarChecker {
    boolean isGuitarOk();
}

Mixin class - GuitarCheckerMixin.class:

public class GuitarCheckerMixin extends DelegatingIntroductionInterceptor implements GuitarChecker {
    @Override
    public boolean isGuitarOk() {
        System.out.println("I don't know how to check the guitar");
        return true;
    }
}

And eventually configuration class with main() method:

@Configuration
@ComponentScan("com.annotation.test")
public class Config {
    @Bean
    public ProxyFactoryBean checkedGuitar() {
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
        Instrument guitar = new Guitar();
        proxyFactoryBean.setTarget(guitar);
        proxyFactoryBean.addAdvisor(new DefaultIntroductionAdvisor(new GuitarCheckerMixin()));
        proxyFactoryBean.setProxyTargetClass(true);
        return proxyFactoryBean;
    }

    public static void main(String[] args) {
        AnnotationConfigApplicationContext appContext
                = new AnnotationConfigApplicationContext(Config.class);
        Singer singer = appContext.getBean(Singer.class);
        singer.singSong();
        Instrument instrument = singer.getInstrument();
        GuitarChecker guitarChecker = (GuitarChecker) instrument;
        guitarChecker.isGuitarOk();
    }
}

If I run "main()", I will get:

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.annotation.test.Instrument' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1790)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1346)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1300)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.resolveMethodArguments(AutowiredAnnotationBeanPostProcessor.java:759)
    ... 17 more

But if I add one of these two steps (works ok with only one of them), it will work correctly and print result.

1 Step) - add @DependsOn("checkedGuitar") to GuitarSinger.class:

@Service
@Lazy
@DependsOn("checkedGuitar")
public class GuitarSinger implements Singer {

2 Step) - add one more line with appContext.getBean("checkedGuitar") to main().

public static void main(String[] args) {
        AnnotationConfigApplicationContext appContext
                = new AnnotationConfigApplicationContext(Config.class);
        appContext.getBean("checkedGuitar");
        Singer singer = appContext.getBean(Singer.class);
        singer.singSong();
        Instrument instrument = singer.getInstrument();
        GuitarChecker guitarChecker = (GuitarChecker) instrument;
        guitarChecker.isGuitarOk();
    }

With one of these two updates code will print the following lines:

I'm singing a song
I'm a guitar!
I don't know how to check the guitar

Could you please help me with understanding of the issue? Why does it work with @DependsOn or getBean()?

Thanks!

CodePudding user response：

It is saying it can't find any Bean that implements an interface Instrument. The only class that you have implementing Instrument is class Guitar. Annotate it with @Component so Spring can find it.

CodePudding user response：

I am not a Spring user, so I do not know how proxy bean factories and the other stuff you use are meant to be used canonically. But how about his?

package de.scrum_master.spring.q70623926;

import org.springframework.aop.framework.ProxyFactoryBean;
import org.springframework.aop.support.DefaultIntroductionAdvisor;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan("de.scrum_master.spring.q70623926")
public class Config {
  @Bean
  public Instrument instrument() {
    return (Instrument) checkedGuitar().getObject();
  }

  @Bean
  public ProxyFactoryBean checkedGuitar() {
    ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
    Instrument instrument = new Guitar();
    proxyFactoryBean.setTarget(instrument);
    proxyFactoryBean.addAdvisor(new DefaultIntroductionAdvisor(new GuitarCheckerMixin()));
    proxyFactoryBean.setProxyTargetClass(true);
    return proxyFactoryBean;
  }

  public static void main(String[] args) {
    try (AnnotationConfigApplicationContext appContext = new AnnotationConfigApplicationContext(Config.class)) {
      Singer singer = appContext.getBean(GuitarSinger.class);
      singer.singSong();
      Instrument instrument = singer.getInstrument();
      GuitarChecker guitarChecker = (GuitarChecker) instrument;
      guitarChecker.isGuitarOk();
    }
  }
}

This yields:

12:39:49.887 [main] DEBUG org.springframework.aop.framework.ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 [main] DEBUG org.springframework.aop.framework.ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 [main] DEBUG org.springframework.aop.framework.ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 [main] DEBUG org.springframework.aop.framework.ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.979 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'guitarSinger'
I'm singing a song
I'm a guitar!
I don't know how to check the guitar
12:39:50.023 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@61baa894, started on Sun Jan 09 12:39:49 ICT 2022