在 Spring Cloud 体系的项目中，配置中心主要用于提供分布式的配置管理，其中有一个重要的注解：@RefreshScope，如果代码中需要动态刷新配置，在需要的类上加上该注解就行。本文分享一下笔者遇到与 @ConditionalOnSingleCandidate 注解冲突的问题

问题背景

项目再引入 RabbitMQ,在自定义 connectionFactory 时，手滑加上了 @RefreshScope

@Bean@RefreshScopepublic CachingConnectionFactory connectionFactory() {    CachingConnectionFactory connectionFactory = new CachingConnectionFactory();    connectionFactory.setAddresses("172.17.0.111");    connectionFactory.setUsername("guest");    connectionFactory.setPassword("guest");    connectionFactory.setVirtualHost("/");    return connectionFactory;}

系统报错无法注入 RabbitTemplate

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'com.pig4cloud.course.refresh.bug.RefreshBugApplicationTest':Unsatisfied dependency expressed through field 'rabbitTemplate'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:No qualifying bean of type 'org.springframework.amqp.rabbit.core.RabbitTemplate' available: expected at least 1 bean which qualifies as autowire candidate.Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

排查

    1. 默认情况下 spring-boot-starter-amqp 会默认给我们注入 rabbitTemplate 实现

RabbitAutoConfiguration#rabbitTemplate

@Bean@ConditionalOnSingleCandidate(ConnectionFactory.class)@ConditionalOnMissingBean(RabbitOperations.class)public RabbitTemplate rabbitTemplate(RabbitTemplateConfigurer configurer, ConnectionFactory connectionFactory) {  RabbitTemplate template = new RabbitTemplate();  configurer.configure(template, connectionFactory);  return template;}
    1. 开启 Spring Boot 启动 debugger 日志，查看注入信息
   RabbitAutoConfiguration.RabbitTemplateConfiguration#rabbitTemplate:      Did not match:         - @ConditionalOnSingleCandidate (types: org.springframework.amqp.rabbit.connection.ConnectionFactory; SearchStrategy: all)         did not find a primary bean from beans 'connectionFactory', 'scopedTarget.connectionFactory' (OnBeanCondition)

提示 ConditionalOnSingleCandidate 注解的方法不能查找到唯一 ConnectionFactory 实现

    1. 使用 @RefreshScope 注解的 bean，默认情况下同时会生成 scopedTarget.beanName的 bean
@Autowiredprivate ApplicationContext context;@Testpublic void testRabbitTemplate() {    String[] beanNames = context.getBeanNamesForType(ConnectionFactory.class);    for (String beanName : beanNames) {        System.out.println(beanName);    }    Assert.isTrue(beanNames.length == 2);}scopedTarget.connectionFactoryconnectionFactory
    1. 由于 ConditionalOnSingleCandidate 成立的条件是全局只能有一个此类型的 bean 所以 默认的 RabbitTemplate 无法注入

常见被 ConditionalOnSingleCandidate 注解的 bean

    1. 使用 JdbcTemplate 无法在自定义 DataSource 添加 @RefreshScope
@ConditionalOnSingleCandidate(DataSource.class)public class JdbcTemplateAutoConfiguration {}
    1. MailSenderValidator 邮件发送校验器无法添加 @RefreshScope
@Configuration(proxyBeanMethods = false)@AutoConfigureAfter(MailSenderAutoConfiguration.class)@ConditionalOnProperty(prefix = "spring.mail", value = "test-connection")@ConditionalOnSingleCandidate(JavaMailSenderImpl.class)public class MailSenderValidatorAutoConfiguration {}
    1. 由于默认情况下涉及的 bean 很多，所以使用 RefreshScope 时一定要避免这些 bean

  • 配套源码： https://github.com/lltx/spring-boot-course/tree/master/v2.3/refresh-scope-bug