Spring AOP Bean 注入(inject)错误？

Question

我在这里检查了测试项目:https://github.com/loesak/spring-aop-injection-bug

给定以下 pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.loesoft</groupId>
    <artifactId>spring-aop-injection-bug</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <properties>
        <spring.framework.bom.version>4.2.0.RELEASE</spring.framework.bom.version>
        <spring.retry.version>1.1.2.RELEASE</spring.retry.version>
        <aspectj.aspectjweaver>1.8.7</aspectj.aspectjweaver>
        <java.version>1.7</java.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.retry</groupId>
            <artifactId>spring-retry</artifactId>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework</groupId>
                <artifactId>spring-framework-bom</artifactId>
                <version>${spring.framework.bom.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.retry</groupId>
                <artifactId>spring-retry</artifactId>
                <version>${spring.retry.version}</version>
            </dependency>
            <dependency>
                <groupId>org.aspectj</groupId>
                <artifactId>aspectjweaver</artifactId>
                <version>${aspectj.aspectjweaver}</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                    <compilerArgument>-Xlint:all</compilerArgument>
                    <showWarnings>true</showWarnings>
                    <showDeprecation>true</showDeprecation>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

和 Spring 配置:

package com.loesoft.spring.aop.injection.bug;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.retry.annotation.EnableRetry;
import org.springframework.retry.annotation.Retryable;

@Configuration
@EnableRetry
public class Proof {

    public static void main(String... args) {
        final AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Proof.class);
        context.registerShutdownHook();
    }

    @Bean
    public BeanThing beanThing() {
        return new BeanThing();
    }

    @Bean
    @Autowired
    public BeanNeedy beanNeedy(BeanThing beanThing) {
        return new BeanNeedy(beanThing);
    }

    public static interface BeanInterface {
        public void doSomething();
    }

    public static class BeanThing implements BeanInterface {

        @Retryable
        public void doSomething() {
            System.out.println("BeanNeedingDependencies doing something");
        }

    }

    public static class BeanNeedy {

        private final BeanThing beanThing;

        public BeanNeedy(BeanThing beanThing) {
            this.beanThing = beanThing;
        }
    }

}

Spring 抛出以下错误:

Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'beanNeedy' defined in com.loesoft.spring.aop.injection.bug.Proof: Unsatisfied dependency expressed through constructor argument with index 0 of type [com.loesoft.spring.aop.injection.bug.Proof$BeanThing]: : No qualifying bean of type [com.loesoft.spring.aop.injection.bug.Proof$BeanThing] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.loesoft.spring.aop.injection.bug.Proof$BeanThing] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:749)
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:464)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1123)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1018)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:305)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:301)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:196)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:834)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:537)
    at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:84)
    at com.loesoft.spring.aop.injection.bug.Proof.main(Proof.java:15)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.loesoft.spring.aop.injection.bug.Proof$BeanThing] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1326)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1072)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:967)
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:813)
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741)
    ... 14 more

我已经追踪到这个事实，即 bean“beanThing”最终成为 JdkDynamicAopProxy，因为它具有接口(interface)，并且在创建 bean“beanNeedy”时尝试查找匹配的 bean 作为 Autowiring 候选者时，代码最终以 ResolvableType# isInstance 不检查 JDK 代理类型的底层类型，也没有找到创建的类型为“BeanThing”的 bean“beanThing”。

我可以通过两种方式解决这个问题。第一种是通过将@EnableRetry 注释字段“proxyTargetClass”设置为“true”或通过删除类BeanThing 上的接口(interface)。

这是一个错误还是我错过了一些我不知道的有关 Spring AOP 的信息？一般来说，这对我来说似乎不正确。我觉得 Spring 应该能够确定 Proxy bean 的底层类型，除非有一些技术原因说明它为什么不能。如果有技术原因无法确定 JDK 代理的底层类型，那么也许 Spring 应该有一些额外的检查来帮助开发人员弄清楚发生了什么。

请记住，这与 Spring Retry 无关(因此未标记)，因为我已经能够使用其他需要用 AOP 代理包装底层 bean 的注释来重现此问题。

Answer 1

来自 JDK 代理 javadocs :

A dynamic proxy class is a class that implements a list of interfaces specified at runtime when the class is created

这意味着代理只能实现 bean 的接口(interface)，而不是它的实例。你不能用代理代替真实的类​​，因为你没有类的方法和变量，只有代理的方法。

I can get around this in two ways. The first by setting the @EnableRetry annotation field "proxyTargetClass" to "true" or by removing the interface on the class BeanThing.

如果设置 proxyTargetClass至 true ，而不是 JDK 代理，Spring 将创建一个 CGLIB 类(当类没有接口(interface)时也会发生这种情况，因为您无法创建没有接口(interface)的 JDK 代理)。
使用 CGLIB，您的 bean 的子类被动态创建，它拦截方法调用。

CGLIB 代理是 BeanThing ，因为它继承自它。 JDK 代理不是 BeanThing ，因为它只是实现了它的接口(interface)。

有第三种方法可以解决您的问题:而不是注入(inject) BeanThing类，注入(inject)它实现的接口(interface)( BeanInterface)。

@Bean
public BeanInterface beanThing() {
    return new BeanThing();
}

// .....

public static class BeanNeedy {

    private final BeanInterface beanThing;

    public BeanNeedy(BeanInterface beanThing) {
        this.beanThing = beanThing;
    }
}

配置

为了启用 CGLIB，您可以使用 @EnableAspectJAutoProxy带有 proxyTargetClass 的注释设置为 true在您的配置类之一中。

@Configuration
@EnableAspectJAutoProxy(proxyTargetClass = true)
public class OneOfYourGlobalConfigConfigs {

}