添加千分尺依赖会导致奇怪的 Spring 代理问题

Question

我有一个带有私有 @Scheduled 方法的简单 Spring Boot 应用程序：

@SpringBootApplication
@EnableScheduling
public class DemoApplication {

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

    @Scheduled(fixedRate = 1000)
    private void scheduledTask() {
        System.out.println("Scheduled task");
    }
}

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<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.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!--<dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-spring-legacy</artifactId>
            <version>1.1.1</version>
        </dependency>
        <dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-registry-prometheus</artifactId>
            <version>1.1.1</version>
        </dependency>-->

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>1.8.11</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.8.11</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

当千分尺依赖项并注释掉一切正常时，但当我取消注释它们时，会发生以下异常：

Caused by: java.lang.IllegalStateException: Need to invoke method 'scheduledTask' found on proxy for target class 'DemoApplication' but cannot be delegated to target bean. Switch its visibility to package or protected.
    at org.springframework.aop.support.AopUtils.selectInvocableMethod(AopUtils.java:133) ~[spring-aop-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.processScheduled(ScheduledAnnotationBeanPostProcessor.java:343) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.postProcessAfterInitialization(ScheduledAnnotationBeanPostProcessor.java:326) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:423) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1633) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    ... 15 common frames omitted

有谁知道下面发生了什么？

编辑：我认为 mictometer 和 aspectJ 依赖项之间存在某种冲突，只有在类路径中都存在时才会出现问题。

Answer 1

Spring 建议通常在可能的情况下使用 JDK 代理实现，它需要一个接口来动态实现（它执行有趣的逻辑，然后委托给您的业务代码）。在这种情况下，您有一个实际的类，因此 Spring 能做的最好的事情就是对其进行子类化。

但是，这里有两个相互矛盾的要求：Spring 想要应用捕获代码度量的建议，但是由于该方法是private，因此不能从子类访问它。（我实际上对它使用私有方法检测和调用您的计划任务感到有些惊讶。）

更改您的方法以protected允许 Spring 在运行时执行此操作（不是实际的 Java 代码，而是等效的生成字节码）：

class DemoApplicationWithAdvice extends DemoApplication {
    @Override
    protected void scheduledTask() {
        // record start time
        super.scheduledTask();
        // write metric with execution time
    }
}