Spring-解决@Configuration的循环依赖问题

简介

问题来源

前几天遇到一个循环依赖问题，是RedissonClient这个bean引起的。RedissonClient是由一个配置类（@Configuration注解的类）提供的，这配置类在初始化时（@PostConstruct注解的方法中）去获取RedissonClient这个bean。我在自动注入（@Autowired）RedissonClient时发现报循环依赖异常，应用无法启动。

为什么配置类要在实例化时获取自己管理的bean呢？因为代码的作者是要把这个配置类作为工具类，这个工具类要用到这个bean。这个工具类是作为Redis分布式锁用的，用到RedissonClient锁相关方法，而我想注入RedissonClient，使用它读写Redis的方法。

本文介绍这个问题是如何引起的，以及如何解决。

题外话

刚遇到这个问题时，我其实有点窃喜的。原因是：这个问题我知道快速解决的方案，也想通过这个问题来深入了解循环依赖的原理。

快速解决的方案是：不进行自动注入，使用时再使用ApplicationContext来获取，对应这篇博客：Spring-ApplicationContext-使用/教程/原理 – 自学精灵

我之前写过关于循环依赖的博客，对循环依赖也算是比较熟悉了，我感觉我能以比较优雅的方式来解决这个问题。循环依赖相关博客为：

Spring-循环依赖的解决方案-实例 – 自学精灵
Spring循环依赖的原理(一)-什么是循环依赖 – 自学精灵

这也说明了写博客的重要性，有问题直接找就行，自己实测过的代码，用起来绝对放心。

问题复现

本处为了简单起见不引用RedisClient依赖，自己写一个简单的类进行示例。

代码

RedissonClient配置类（工具类）

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        RedisLockUtil.redissonClient = applicationContext.getBean(RedissonClient.class);
        // System.out.println("This is AUtil#init");
    }

    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

RedissonClient类

package com.example.entity;

public class RedissonClient {
    public void getLock(String string) {
        System.out.println("RedissonClient#getLock:" + string);
    }

    public void getMap() {
        System.out.println("RedissonClient#getMap");
    }
}

我这里为了示例 ，直接打印参数，返回值也直接写为void。

启动类

package com.example;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
    @Autowired
    private RedissonClient redissonClient;

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

}

如果在其他地方注入RedissonClient，有可能不会循环依赖，有可能会循环依赖，这是与bean的扫描顺序有关系的。本处为了百分百复现，直接在启动类注入。

启动时的报错打印

这个打印太长了，但都比较重要。所以我将它单独作为一个二级标题，可以快速在其他内容与这个错误打印之间跳转。

Connected to the target VM, address: '127.0.0.1:54749', transport: 'socket'

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.0.RELEASE)

2021-09-24 23:30:07.025  INFO 13560 --- [           main] com.example.DemoApplication              : Starting DemoApplication on DESKTOP-QI6B9ME with PID 13560 (E:\work\Idea_proj\demo_JAVA\demo_SpringBoot\target\classes started by Liu in E:\work\Idea_proj\demo_JAVA\demo_SpringBoot)
2021-09-24 23:30:07.027  INFO 13560 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default
2021-09-24 23:30:08.312  INFO 13560 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-09-24 23:30:08.321  INFO 13560 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-09-24 23:30:08.321  INFO 13560 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.35]
2021-09-24 23:30:08.430  INFO 13560 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-09-24 23:30:08.430  INFO 13560 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1365 ms
2021-09-24 23:30:08.481  WARN 13560 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoApplication': Unsatisfied dependency expressed through field 'redissonClient'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'redisLockUtil': Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'getRedissonClient': Requested bean is currently in creation: Is there an unresolvable circular reference?
2021-09-24 23:30:08.483  INFO 13560 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2021-09-24 23:30:08.493  INFO 13560 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-09-24 23:30:08.506 ERROR 13560 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoApplication': Unsatisfied dependency expressed through field 'redissonClient'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'redisLockUtil': Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'getRedissonClient': Requested bean is currently in creation: Is there an unresolvable circular reference?
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:643) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:130) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1422) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:895) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at com.example.DemoApplication.main(DemoApplication.java:14) [classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'redisLockUtil': Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'getRedissonClient': Requested bean is currently in creation: Is there an unresolvable circular reference?
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:160) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:416) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1788) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:409) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1338) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:557) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1306) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1226) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:640) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	... 20 common frames omitted
Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'getRedissonClient': Requested bean is currently in creation: Is there an unresolvable circular reference?
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.beforeSingletonCreation(DefaultSingletonBeanRegistry.java:347) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:219) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:227) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1174) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveBean(DefaultListableBeanFactory.java:422) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:352) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:345) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1126) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at com.example.config.RedisLockUtil.init(RedisLockUtil.java:21) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(InitDestroyAnnotationBeanPostProcessor.java:389) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeInitMethods(InitDestroyAnnotationBeanPostProcessor.java:333) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:157) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	... 41 common frames omitted

2021-09-24 23:30:08.510  WARN 13560 --- [           main] o.s.boot.SpringApplication               : Unable to close ApplicationContext

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'springApplicationAdminRegistrar' defined in class path resource [org/springframework/boot/autoconfigure/admin/SpringApplicationAdminJmxAutoConfiguration.class]: Unsatisfied dependency expressed through method 'springApplicationAdminRegistrar' parameter 1; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.core.env.Environment' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:798) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:539) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1338) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:557) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:207) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.event.AbstractApplicationEventMulticaster.retrieveApplicationListeners(AbstractApplicationEventMulticaster.java:245) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.event.AbstractApplicationEventMulticaster.getApplicationListeners(AbstractApplicationEventMulticaster.java:197) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:134) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:403) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:360) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.boot.availability.AvailabilityChangeEvent.publish(AvailabilityChangeEvent.java:81) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.availability.AvailabilityChangeEvent.publish(AvailabilityChangeEvent.java:67) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.doClose(ServletWebServerApplicationContext.java:167) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.close(AbstractApplicationContext.java:978) ~[spring-context-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.boot.SpringApplication.handleRunFailure(SpringApplication.java:814) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:325) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
	at com.example.DemoApplication.main(DemoApplication.java:14) [classes/:na]
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.core.env.Environment' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1716) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1272) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1226) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:885) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:789) ~[spring-beans-5.2.6.RELEASE.jar:5.2.6.RELEASE]
	... 23 common frames omitted

Disconnected from the target VM, address: '127.0.0.1:54749', transport: 'socket'

原因分析

简要分析

我摘抄上边“启动时的报错打印”的最重要的部分：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘demoApplication’: Unsatisfied dependency expressed through field ‘redissonClient’; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘redisLockUtil’: Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name ‘getRedissonClient’: Requested bean is currently in creation: Is there an unresolvable circular reference?

错误大概是这样的：DemoApplication=> RedissonClient=> RedisLockUtil的初始化方法=> getRedissonClient（也就是获取RedissonClient这个bean）。

用人话来表述：创建DemoApplication这个bean时，依赖了RedissonClient，所以去创建RedissonClient，RedissonClient由RedisLockUtil管理的，所以先创建RedisLockUtil，创建RedisLockUtil时的初始化方法又依赖了RedissonClient，导致循环依赖。

详细分析

实例化顺序

RedisLockUtil提供RedissonClient这个bean，初始化时却获取不到，这应该是RedissonClient这个bean的实例化在RedisLockUtil的实例化之后导致的。打个断点验证一下：

启动后发现，果然，先到达21行那个断点。

RedissonClient何时会实例化？

什么时候会去实例化RedissonClient这个bean呢，整个流程如何？（这里有助于理解bean实例化）。本处进行分析。

为了代码能走到RedissonClient实例化的地方，我把上边会报错的地方换掉：

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        // RedisLockUtil.redissonClient = applicationContext.getBean(RedissonClient.class);
        System.out.println("This is RedisLockUtil#init");
    }

    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

打两个断点：

第1个断点到达：

解释：先实例化RedisLockUtil，再调用到期init方法，就到了我们的第1个断点。

第2个断点到达：

 解释：通过factoryBean（即RedisLockUtil）和beanName（即getRedissonClient）来实例化获取RedissonClient这个bean。

可以发现，两个断点，红框中是最靠近的一个共同的方法。通过它的名字instantiateUsingFactoryMethod可以知道，是通过工厂方法来实例化RedissonClient，这个工厂就是RedisLockUtil。

已经够清晰了。我注入一个RedissonClient来使用，Spring去容器里查找，发现它受RedisLockUtil管理，于是先实例化它，实例化后调用其初始化方法（@PostConstruct注解的方法），初始化方法里也是想获取RedissonClient，而这时RedissonClient还没有呢！所以就报错！

解决方案

下边5种解决方案。第5种为最好的方案。

公共代码

package com.example.entity;

public class RedissonClient {
    public void getLock(String string) {
        System.out.println("RedissonClient#getLock:" + string);
    }

    public void getMap() {
        System.out.println("RedissonClient#getMap");
    }
}

这个类都会用到，所以我放到这个公共位置。 

方案1：不自动注入

SpringBoot启动时会扫描所有被@Component注解的bean，然后去扫描这个bean里边的字段，如果它有@Autowired注解，那就从Spring容器中找它然后将引用地址赋值给这个字段，如果找不到则去实例化它。

本文的使用@Autowired注入RedissonClient就是这样，启动时去实例化它导致的失败。

所以思路很简单，我不自动注入，我使用的时候再获取，这样启动时就不会去实例化它。获取的方法为：使用ApplicationContext。想详细了解ApplicationContext的可以见此文。

写法如下：

ApplicationContext工具类

package com.example.util;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
 
@Component
public class ApplicationContextHolder implements ApplicationContextAware {
    private static ApplicationContext context;
 
    @Override
    public void setApplicationContext(ApplicationContext context)
            throws BeansException {
        ApplicationContextHolder.context = context;
    }
 
    public static ApplicationContext getContext() {
        return context;
    }
}

启动类

package com.example;

import com.example.entity.RedissonClient;
import com.example.util.ApplicationContextHolder;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
    private static RedissonClient redissonClient;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
        DemoApplication.redissonClient = ApplicationContextHolder.getContext().getBean(RedissonClient.class);
        DemoApplication.redissonClient.getMap();
    }

}

原来的配置类不变

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        RedisLockUtil.redissonClient = applicationContext.getBean(RedissonClient.class);
        // System.out.println("This is RedisLockUtil#init");
    }

    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

启动测试

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.0.RELEASE)

2021-09-25 10:10:23.936  INFO 49756 --- [           main] com.example.DemoApplication              : Starting DemoApplication on DESKTOP-QI6B9ME with PID 49756 (E:\work\Idea_proj\demo_JAVA\demo_SpringBoot\target\classes started by Liu in E:\work\Idea_proj\demo_JAVA\demo_SpringBoot)
2021-09-25 10:10:23.936  INFO 49756 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default
2021-09-25 10:10:24.896  INFO 49756 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-09-25 10:10:24.896  INFO 49756 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-09-25 10:10:24.896  INFO 49756 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.35]
2021-09-25 10:10:25.001  INFO 49756 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-09-25 10:10:25.001  INFO 49756 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1028 ms
2021-09-25 10:10:25.316  INFO 49756 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2021-09-25 10:10:25.431  INFO 49756 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2021-09-25 10:10:25.586  INFO 49756 --- [           main] com.example.DemoApplication              : Started DemoApplication in 1.944 seconds (JVM running for 2.964)
RedissonClient#getMap

 可见：正常启动了。

方案2：延迟注入

Spring有延迟注入的方法，使用的时候再去实例化这个bean，而不是启动时就实例化，见这里：Spring-延迟加载(@Lazy注解等)-使用/原理 – 自学精灵

启动类

package com.example;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Lazy;

@SpringBootApplication
public class DemoApplication {
    @Lazy
    @Autowired
    private RedissonClient redissonClient;

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

}

这样就可以启动成功了。 

方案3：用方法获得bean

此方法更简单了，对代码的改动最小。

原来配置类是这样的：

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        RedisLockUtil.redissonClient = applicationContext.getBean(RedissonClient.class);
    }

    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

修改之后： 

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @PostConstruct
    public void init() {
        RedisLockUtil.redissonClient = getRedissonClient();
    }

    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

可以看到，我直接调用本类里获取bean的方法来拿的bean。这样是可以的，也是可以保证RedissonClient的单例模式，没有任何影响。项目也可以启动成功。

看到这里，应该要有疑问了。

疑问一：我是怎么知道可以通过这种方法来获得本类中的bean的？

这种用法是我自己在使用shiro框架时，看到其他人这样写的，就知道了这种用法。可见，技术是相通的，了解的多了，思路就会更多。

疑问2：这样为什么仍然可以保证单例模式，这样获取的bean会加入Spring容器的管理吗？

答案是：会加入Spring容器的管理。

接下来，我就分析一下，为什么它可以加入Spring容器的管理。老方法，加断点：

首先到达第22行的断点：

然后一直点击箭头所指的位置（单步），一直找到它加入Spring容器的地方：

看到红框中的代码，也就是说，它会加入Spring容器，下次有其他地方需要这个bean的时候，会直接获取这个bean，而不是新构造一个了。

有朋友可能会问，我怎么知道红框中的代码是加入Spring容器的代码。我之前分析过循环依赖的详细原理，所以我一眼就能看出这是第三级缓存。循环依赖的详细原理以及三级缓存，可以见我的这篇博客：Spring循环依赖的原理(一)-什么是循环依赖 – 自学精灵

方案4：bean放到外部管理

对于这个RedisLockUtil配置类，它同时也是工具类，它用到了RedissonClient的锁功能，其实RedissonClient的其他读写Redis的方法也巨好用，就像操作JDK中的List、Set、Map一样，RedissonClient实际是实现了JDK中的List、Set、Map，所以使用RedissonClient操作Redis就像我们操作JDK的List、Set、Map一样，超级便利。基于此，我把RedissonClient的配置单独拿出来。

修改之前

配置类（工具类）

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        RedisLockUtil.redissonClient = applicationContext.getBean(RedissonClient.class);
    }

    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

启动类 

package com.example;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
    @Autowired
    private RedissonClient redissonClient;

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

}

修改之后

配置类（工具类） 

package com.example.util;

import com.example.entity.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        RedisLockUtil.redissonClient = applicationContext.getBean(RedissonClient.class);
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

配置类 

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class RedissonConfig {
    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }
}

 启动类不变

测试修改后的结果

可以启动成功。

方案5：工具类不加入容器（推荐）

思考一下：RedisLockUtil是个工具类，我们想用的是它的静态方法，所以，最好不将其加入容器。本方案为最优方案，个人感觉是最优雅的方案。

工具类

package com.example.util;

import com.example.entity.RedissonClient;

public class RedisLockUtil {
    private static RedissonClient redissonClient;
    private static final String PREFIX = "rbac:user:" ;

    static {
        System.out.println("RedisLockUtil.static initializer");
        RedisLockUtil.redissonClient = ApplicationContextHolder.getContext().getBean(RedissonClient.class);
    }

    public static void lock(String name) {
        RedisLockUtil.redissonClient.getLock(PREFIX + name);
    }
}

RedissonClient

package com.example.entity;

public class RedissonClient {
    public void getLock(String string) {
        System.out.println("RedissonClient#getLock:" + string);
    }

    public void getMap() {
        System.out.println("RedissonClient#getMap");
    }
}

Redisson配置类

package com.example.config;

import com.example.entity.RedissonClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class RedissonConfig {
    @Bean
    public RedissonClient getRedissonClient() {
        return new RedissonClient();
    }
}

ApplicationContext工具类

package com.example.util;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
 
@Component
public class ApplicationContextHolder implements ApplicationContextAware {
    private static ApplicationContext context;
 
    @Override
    public void setApplicationContext(ApplicationContext context) throws BeansException {
        ApplicationContextHolder.context = context;
    }
 
    public static ApplicationContext getContext() {
        return context;
    }
}

启动类

package com.example;

import com.example.entity.RedissonClient;
import com.example.util.RedisLockUtil;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
    @Autowired
    private RedissonClient redissonClient;

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

}

测试启动

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.0.RELEASE)

2021-09-25 12:18:03.232  INFO 5528 --- [           main] com.example.DemoApplication              : Starting DemoApplication on DESKTOP-QI6B9ME with PID 5528 (E:\work\Idea_proj\demo_JAVA\demo_SpringBoot\target\classes started by Liu in E:\work\Idea_proj\demo_JAVA\demo_SpringBoot)
2021-09-25 12:18:03.234  INFO 5528 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default
2021-09-25 12:18:04.380  INFO 5528 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-09-25 12:18:04.388  INFO 5528 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-09-25 12:18:04.388  INFO 5528 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.35]
2021-09-25 12:18:04.499  INFO 5528 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-09-25 12:18:04.499  INFO 5528 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1226 ms
2021-09-25 12:18:04.896  INFO 5528 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2021-09-25 12:18:05.024  INFO 5528 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2021-09-25 12:18:05.202  INFO 5528 --- [           main] com.example.DemoApplication              : Started DemoApplication in 2.299 seconds (JVM running for 3.382)
RedisLockUtil.static initializer
RedissonClient#getLock:rbac:user:Tony