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SpringBoot自动加载机制,是SpringBoot的核心机制之一
SpringBoot自动加载,是依赖spring-boot-autoconfigure
模块完成的
https://blog.csdn.net/yeyinglingfeng/article/details/87790700
机制流程
启动
自动加载的启动,来自SpringBoot启动时的上下文刷新时
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
配置类定义
以Redis为例,配置类如下
@Configuration
@ConditionalOnClass(RedisOperations.class)
@EnableConfigurationProperties(RedisProperties.class)
@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })
public class RedisAutoConfiguration {
...
}
注意的是,配置类并不在Redis模块spring-data-redis
,而是在模块spring-boot-autoconfigure
中
这代表着无论是否使用Redis,Redis配置类是始终跟随Project走的
但是这并不意味着会真正加载Redis配置,原因在于加载条件是@ConditionalOnClass(RedisOperations.class)
,而RedisOperations.class
是在真正的Redis模块中的
也就是说,这个配置会始终跟随Project,但必须在真正引入Redis模块,才会真正被加载,否则加载将被跳过