SpringBoot bean查询加载顺序流程详解
目录
- 背景
- 探索-源码
- 进一步思考
背景
SpringBoot bean 加载顺序如何查看,想看加载了哪些bean, 这些bean的加载顺序是什么?
实际加载顺序不受控制,但会有一些大的原则:
1、按照字母顺序加载(同一文件夹下按照字母数序;不同文件夹下,先按照文件夹命名的字母顺序加载)
2、不同的bean声明方式不同的加载时机,顺序总结:@ComponentScan > @Import > @Bean
这里的ComponentScan指@ComponentScan及其子注解,Bean指的是@configuration + @bean
同时需要注意的是:
(1)Component及其子注解申明的bean是按照字母顺序加载的
(2)@configuration + @bean是按照定义的顺序依次加载的
(3)@import的顺序,就是bean的加载顺序
(4)在xml中,通过<bean id="">方式声明的bean也是按照代码的编写顺序依次加载的
(5)同一类中加载顺序:Constructor >> @Autowired >> @PostConstruct >> @Bean
(6)同一类中加载顺序:静态变量 / 静态代码块 >> 构造代码块 >> 构造方法(需要特别注意的是静态代码块的执行并不是优先所有的bean加载,只是在同一个类中,静态代码块优先加载)
探索-源码
入口:
public class TestApplication { public static void main(String[] args) { try { SpringApplication.run(TestApplication.class, args); LOGGER.info("SpringBoot Application Start!!!"); } catch (Throwable e) { throw e; } } }
其中 里面的run方法为:
public ConfigurableApplicationContext run(String... args) { long startTime = System.nanoTime(); DefaultBootstrapContext bootstrapContext = createBootstrapContext(); ConfigurableApplicationContext context = null; configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(bootstrapContext, this.mainApplicationClass); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments); configureIgnoreBeanInfo(environment); Banner printedBanner = printBanner(environment); context = createApplicationContext(); context.setApplicationStartup(this.applicationStartup); prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner); **refreshContext**(context); afterRefresh(context, applicationArguments); Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup); } listeners.started(context, timeTakenToStartup); callRunners(context, applicationArguments); } catch (Throwable ex) { handleRunFailure(context, ex, listeners); throw new IllegalStateException(ex); } try { Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime); listeners.ready(context, timeTakenToReady); } catch (Throwable ex) { handleRunFailure(context, ex, null); throw new IllegalStateException(ex); } return context; }
refreshContext(context);
private void refreshContext(ConfigurableApplicationContext context) { if (this.registerShutdownHook) { shutdownHook.registerApplicationContext(context); } **refresh**(context); }
AbstractApplicationContext#refresh
然后看倒数第二行:finishBeanFactoryInitialization(beanFactory);
org.springframework.context.support.AbstractApplicationContext#refresh
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh"); // 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); // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process"); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); beanPostProcess.end(); // 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(); }
finishBeanFactoryInitialization(beanFactory)
然后看最后一行:beanFactory.preInstantiateSingletons();
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // Initialize conversion service for this context. if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { beanFactory.setConversionService( beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)); } // Register a default embedded value resolver if no BeanFactoryPostProcessor // (such as a PropertySourcesPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values. if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); } // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early. String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) { getBean(weaverAwareName); } // Stop using the temporary ClassLoader for type matching. beanFactory.setTempClassLoader(null); // Allow for caching all bean definition metadata, not expecting further changes. beanFactory.freezeConfiguration(); // Instantiate all remaining (non-lazy-init) singletons. **beanFactory.preInstantiateSingletons();** }
beanFactory.preInstantiateSingletons()
在这里会对 beanDefinitionNames 进行遍历,然后进行 bean的实例化 和 组装
因此这里的 beanDefinitionNames 这个列表决定了bean 的 注册顺序。
org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons
@Override public void preInstantiateSingletons() throws BeansException { if (logger.isTraceEnabled()) { logger.trace("Pre-instantiating singletons in " + this); } // Iterate over a copy to allow for init methods which in turn register new bean definitions. // While this may not be part of the regular factory bootstrap, it does otherwise work fine. **List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);** // Trigger initialization of all non-lazy singleton beans... for (String beanName : beanNames) { RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { if (isFactoryBean(beanName)) { Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); if (bean instanceof FactoryBean) { FactoryBean<?> factory = (FactoryBean<?>) bean; boolean isEagerInit; if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { isEagerInit = AccessController.doPrivileged( (PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit, getAccessControlContext()); } else { isEagerInit = (factory instanceof SmartFactoryBean && ((SmartFactoryBean<?>) factory).isEagerInit()); } if (isEagerInit) { getBean(beanName); } } } else { getBean(beanName); } } } // Trigger post-initialization callback for all applicable beans... for (String beanName : beanNames) { Object singletonInstance = getSingleton(beanName); if (singletonInstance instanceof SmartInitializingSingleton) { StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize") .tag("beanName", beanName); SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; if (System.getSecurityManager() != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { smartSingleton.afterSingletonsInstantiated(); return null; }, getAccessControlContext()); } else { smartSingleton.afterSingletonsInstantiated(); } smartInitialize.end(); } } }
如果不能看,像图中一样,不能找到java.util.list这个类,可以使用下面这个方式,亲测有效:
beanDefinitionNames.toArray()
后面的bean就不展示顺序了。感兴趣的读者可以看自己springBoot项目的。
进一步思考
beanDefinitionNames 列表如何来的呢?
答案是 ConfigurationClassPostProcessor 通过扫描 代码+注解生成的,讲bean 扫描解析成 beanDefinition, 同时把 bean定义,beanDefinition,注册到 BeanDefinitionRegistry, 故有了beanDefinitionNames list。
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