为什么 ProxyFactoryBean 会使用 @Autowired 抛出“No qualifying bean of type”？并且不使用 pre-getBean() 抛出？

Question

我尝试将ProxyFactoryBean 与@Autowired 一起使用，但它会在setInstrument 方法处引发异常。

问题 - 为什么它适用于以前称为 getBean 的方法或 @DependsOn？我试图了解 Spring 对这些额外步骤的执行情况。

提前谢谢你！

我有两个接口 - Singer 和 Instrument。以及它们的两个实现 - GuitarSinger.class 和 Guitar.class。

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

@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();
    }
}

public interface Instrument {
    void play();
}

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

此接口用于代理介绍：

public interface GuitarChecker {
    boolean isGuitarOk();
}

这个混入类实现了我们要引入代理的接口：

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;
    }
}

最终，带有main 方法的配置类：

@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();
    }
}

如果我运行main，我会得到：

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

但是如果我添加这两个步骤之一（只使用其中一个就可以），它将正常工作并打印结果。

1. 将@DependsOn("checkedGuitar") 添加到GuitarSinger：

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

2. 在main 中再添加一行appContext.getBean("checkedGuitar")。

    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();
    }
   

通过这两个更新之一，应用程序将打印以下行：

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

您能帮我理解这个问题吗？为什么它适用于@DependsOn 或getBean()？

Answer 1

我不是 Spring 用户，所以我不知道代理 bean 工厂和您使用的其他东西是如何规范使用的。但是他的呢？

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 ProxyFactoryBean checkedGuitar() throws ClassNotFoundException {
    ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
    proxyFactoryBean.setTarget(new Guitar());
    proxyFactoryBean.setProxyTargetClass(true);
    // Make CGLIB proxy implement the same interfaces as the target class
    proxyFactoryBean.setProxyInterfaces(Guitar.class.getInterfaces());
    proxyFactoryBean.addAdvisor(new DefaultIntroductionAdvisor(new GuitarCheckerMixin()));
    return proxyFactoryBean;
  }

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

这会产生：

12:39:49.887 ...ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 ...ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 ...ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 ...ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.887 ...ProxyFactoryBean - Advice has changed; re-caching singleton instance
12:39:49.979 ...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 ...AnnotationConfigApplicationContext - Closing ...AnnotationConfigApplicationContext@61baa894, ...

Answer 2

这是说它找不到任何实现接口Instrument 的Bean。您实现Instrument 的唯一类是Guitar 类。用 @Component 注释它，以便 Spring 可以找到它。