SpringApplication

SpringApplication類提供了一種方便的方法來引導從main()方法啟動的Spring應用程式

SpringBoot 包掃描註解源碼分析

@SpringBootApplication
public class Springbootv2Application {
   public static void main(String[] args) {
      //創建ApplicationContext並啟動
      new SpringApplication(Springbootv2Application.class).run(args);
   }
}

/**
 * Run the Spring application, creating and refreshing a new
 * {@link ApplicationContext}.
 * @param args the application arguments (usually passed from a Java main method)
 * @return a running {@link ApplicationContext}
 */
public ConfigurableApplicationContext run(String... args) {
   StopWatch stopWatch = new StopWatch();
   //記錄應用啟動時間
   stopWatch.start();
   ConfigurableApplicationContext context = null;
   Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    
   configureHeadlessProperty();
   //啟動SpringApplicationRunListener
   SpringApplicationRunListeners listeners = getRunListeners(args);
   listeners.starting();
   try {
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(
            args);
      ConfigurableEnvironment environment = prepareEnvironment(listeners,
            applicationArguments);
      configureIgnoreBeanInfo(environment);
       //列印banner
      Banner printedBanner = printBanner(environment);
      //創建applicationContext 我們這次的重點在這裡面
      context = createApplicationContext();
      exceptionReporters = getSpringFactoriesInstances(
            SpringBootExceptionReporter.class,
            new Class[] { ConfigurableApplicationContext.class }, context);
      prepareContext(context, environment, listeners, applicationArguments,
            printedBanner);
      refreshContext(context);
      afterRefresh(context, applicationArguments);
      stopWatch.stop();
      if (this.logStartupInfo) {
         new StartupInfoLogger(this.mainApplicationClass)
               .logStarted(getApplicationLog(), stopWatch);
      }
      listeners.started(context);
      callRunners(context, applicationArguments);
   }
   catch (Throwable ex) {
      handleRunFailure(context, ex, exceptionReporters, listeners);
      throw new IllegalStateException(ex);
   }
​
   try {
      listeners.running(context);
   }
   catch (Throwable ex) {
      handleRunFailure(context, ex, exceptionReporters, null);
      throw new IllegalStateException(ex);
   }
   return context;
}

我們來看下spring boot裡面是怎麼創建applicationContext的：

protected ConfigurableApplicationContext createApplicationContext() {
   Class<?> contextClass = this.applicationContextClass;
   if (contextClass == null) {
      try {
         //主要是根據webApplicationType這個屬性
         switch (this.webApplicationType) {
         case SERVLET:
            //如果是SERVLET創建"org.springframework.boot.
            //web.servlet.context.AnnotationConfigServletWebServerApplicationContext"
            contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
            break;
         case REACTIVE:
             //如果是REACTIVE創建"org.springframework.
        //boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext"
            contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
            break;
         default:
            //預設是創建org.springframework.context.
            //annotation.AnnotationConfigApplicationContext
            contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
         }
      }
      catch (ClassNotFoundException ex) {
         throw new IllegalStateException(
               "Unable create a default ApplicationContext, "
                     + "please specify an ApplicationContextClass",
               ex);
      }
   }
   return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

我們來看下webApplicationType這個屬性是怎麼取值的：

static WebApplicationType deduceFromClasspath() {
    /**
    **  如果程式中有org.springframework.web.reactive.DispatcherHandler這個類且沒有
    **　org.springframework.web.servlet.DispatcherServlet和　　
    **　org.glassfish.jersey.servlet.ServletContainer　這兩類那麼就是REACTIVE
    **/
   if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null)
         && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
         && !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
      return WebApplicationType.REACTIVE;
   }
   //SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet",
    //      "org.springframework.web.context.ConfigurableWebApplicationContext" }
    // 如果程式中這兩個類有一個不存在就是NONE
   for (String className : SERVLET_INDICATOR_CLASSES) {
      if (!ClassUtils.isPresent(className, null)) {
         return WebApplicationType.NONE;
      }
   }
    //如果上面都不是那就是SERVLET
   return WebApplicationType.SERVLET;
}

根據上面的代碼我們可以看出如果我們不引入reactive和web的依賴那麼我們的程式預設就是使用的NONE,對應的

ApplicationContext就是AnnotationConfigApplicationContext這個類,接下來我們再看下這個類的構造方法:

public AnnotationConfigApplicationContext() {
   //創建一個AnnotatedBeanDefinitionReader
   this.reader = new AnnotatedBeanDefinitionReader(this);
   this.scanner = new ClassPathBeanDefinitionScanner(this);
}
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
   Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
   Assert.notNull(environment, "Environment must not be null");
   this.registry = registry;
   this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
   //註冊AnnotationConfigProcessors　重點看這裡
   AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
      BeanDefinitionRegistry registry, @Nullable Object source) {
​
   DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
   if (beanFactory != null) {
      if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
         beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
      }
      if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
         beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
      }
   }
​
   Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
​
   // 如果registry不包含ConfigurationClassPostProcessor這個類信息時註冊到registry
   if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
   }
   //註冊AutowiredAnnotationBeanPostProcessor
   if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
   }
​
   // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
   if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
   }
​
   // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
   //是否需要支持jpa 是的話註冊對應的bean
   if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition();
      try {
         def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
               AnnotationConfigUtils.class.getClassLoader()));
      }
      catch (ClassNotFoundException ex) {
         throw new IllegalStateException(
               "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
      }
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
   }
    
   if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
   }
​
   if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
      RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
   }
​
   return beanDefs;
}

看到這裡我們先記著我們註冊了ConfigurationClassPostProcessor 和AutowiredAnnotationBeanPostProcessor這兩個類，我們繼續往下看，我們現在來看refreshContext(context)的流程我們根據代碼可以看到

protected void refresh(ApplicationContext applicationContext) {
   Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
    //刷新applicationContext
   ((AbstractApplicationContext) applicationContext).refresh();
}

上面代碼調用到ApplicationContext的refresh　因為我們程式根據依賴推導出我們的ApplicationContext是AnnotationConfigApplicationContext這個類，所以我們來看下AnnotationConfigApplicationContext的refresh方法：

因為AnnotationConfigApplicationContext是繼承於AbstractApplicationContext這個類的，所以我們的refresh就是AbstractApplicationContext的refresh方法：

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.
         //調用程式里的BeanFactoryPostProcessors
         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();
      }
   }
}

因為我們這次主要是要看spring boot是怎麼掃描包的　所以我們重點看invokeBeanFactoryPostProcessors這個方法，在這之前我們先記住ConfigurationClassPostProcessor的類圖：

因為方法太長所以我去掉了一些不是這次重點的代碼：

public static void invokeBeanFactoryPostProcessors(
      ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
​
   // Invoke BeanDefinitionRegistryPostProcessors first, if any.
   Set<String> processedBeans = new HashSet<>();
    ...
      // Do not initialize FactoryBeans here: We need to leave all regular beans
      // uninitialized to let the bean factory post-processors apply to them!
      // Separate between BeanDefinitionRegistryPostProcessors that implement
      // PriorityOrdered, Ordered, and the rest.
      List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
​
      // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
      //記得我們之前註冊的ConfigurationClassPostProcessor嗎，因為他是實現了BeanDefinitionRegistryPostProcessor介面的，所以這裡會被取到
      String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
          // ConfigurationClassPostProcessor　類同時也實現了PriorityOrdered介面
         if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
             //創建ConfigurationClassPostProcessor對象並把它加到list中
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
         }
      }
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
    　//調用方法
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
      currentRegistryProcessors.clear();
​
     ...
   beanFactory.clearMetadataCache();
}

繼續跟蹤代碼的話會調用到ConfigurationClassPostProcessor的processConfigBeanDefinitions方法

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
   List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
   String[] candidateNames = registry.getBeanDefinitionNames();
​
   ...
​
   // Parse each @Configuration class
   ConfigurationClassParser parser = new ConfigurationClassParser(
         this.metadataReaderFactory, this.problemReporter, this.environment,
         this.resourceLoader, this.componentScanBeanNameGenerator, registry);
​
   Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
   Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
   do {
      //這裡我們只有我們的啟動類Springbootv2Application　這個parser是ConfigurationClassParser所以我們進入它的parse方法
      parser.parse(candidates);
      parser.validate();
​
     ...
}

最後會進入下麵這方法

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
   ...
   // Recursively process the configuration class and its superclass hierarchy.
   //獲得我們的啟動類全名　xxx.xxx.Springbootv2Application
   SourceClass sourceClass = asSourceClass(configClass);
   do {
       //spring 的命名規則就是do開頭的就是真正幹活的地方
      sourceClass = doProcessConfigurationClass(configClass, sourceClass);
   }
   while (sourceClass != null);
​
   this.configurationClasses.put(configClass, configClass);
}

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
      throws IOException {
    ...
   // Process any @ComponentScan annotations
   //獲取啟動類的componentScans屬性
   Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
         sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
   if (!componentScans.isEmpty() &&
         !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
      for (AnnotationAttributes componentScan : componentScans) {
         // The config class is annotated with @ComponentScan -> perform the scan immediately
          //掃描beanDefinition
         Set<BeanDefinitionHolder> scannedBeanDefinitions =
               this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
         // Check the set of scanned definitions for any further config classes and parse recursively if needed
         for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
            BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
            if (bdCand == null) {
               bdCand = holder.getBeanDefinition();
            }
            if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
               parse(bdCand.getBeanClassName(), holder.getBeanName());
            }
         }
      }
   }
​
  ...
   return null;
}

下麵就是重點了：

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
   ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
         componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);
    
   Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
   boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
   scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
         BeanUtils.instantiateClass(generatorClass));
    //配置scanner的屬性
   ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
   if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
      scanner.setScopedProxyMode(scopedProxyMode);
   }
   else {
      Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
      scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
   }
    
   scanner.setResourcePattern(componentScan.getString("resourcePattern"));
​
   for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
      for (TypeFilter typeFilter : typeFiltersFor(filter)) {
         scanner.addIncludeFilter(typeFilter);
      }
   }
   for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
      for (TypeFilter typeFilter : typeFiltersFor(filter)) {
         scanner.addExcludeFilter(typeFilter);
      }
   }
​
   boolean lazyInit = componentScan.getBoolean("lazyInit");
   if (lazyInit) {
      scanner.getBeanDefinitionDefaults().setLazyInit(true);
   }
​
   Set<String> basePackages = new LinkedHashSet<>();
   String[] basePackagesArray = componentScan.getStringArray("basePackages");
   for (String pkg : basePackagesArray) {
      String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
      Collections.addAll(basePackages, tokenized);
   }
   for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
      basePackages.add(ClassUtils.getPackageName(clazz));
   }
   //重點就是這裡，如果我們沒有配置basePackages的話那麼這裡就取啟動類的包名
   if (basePackages.isEmpty()) {
      basePackages.add(ClassUtils.getPackageName(declaringClass));
   }
​
   scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
      @Override
      protected boolean matchClassName(String className) {
         return declaringClass.equals(className);
      }
   });
   //這裡就是掃描包下的類，這裡是數組如果我們有配置的話就是我們配置的包，沒有的話就是啟動類的包名
   return scanner.doScan(StringUtils.toStringArray(basePackages));
}

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
   Set<BeanDefinition> candidates = new LinkedHashSet<>();
   try {
       //掃描包下的所有**/*.class
      String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
            resolveBasePackage(basePackage) + '/' + this.resourcePattern;
      Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
      boolean traceEnabled = logger.isTraceEnabled();
      boolean debugEnabled = logger.isDebugEnabled();
      for (Resource resource : resources) {
         if (traceEnabled) {
            logger.trace("Scanning " + resource);
         }
         if (resource.isReadable()) {
            try {
               MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
                //這裡會排除掉不需要註冊的bean
               if (isCandidateComponent(metadataReader)) {
                  ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
                  sbd.setResource(resource);
                  sbd.setSource(resource);
                  if (isCandidateComponent(sbd)) {
                     if (debugEnabled) {
                        logger.debug("Identified candidate component class: " + resource);
                     }
                     candidates.add(sbd);
                  }
                  else {
                     if (debugEnabled) {
                        logger.debug("Ignored because not a concrete top-level class: " + resource);
                     }
                  }
               }
               else {
                  if (traceEnabled) {
                     logger.trace("Ignored because not matching any filter: " + resource);
                  }
               }
            }
            catch (Throwable ex) {
               throw new BeanDefinitionStoreException(
                     "Failed to read candidate component class: " + resource, ex);
            }
         }
         else {
            if (traceEnabled) {
               logger.trace("Ignored because not readable: " + resource);
            }
         }
      }
   }
   catch (IOException ex) {
      throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
   }
   return candidates;
}

源碼太多，我這裡去掉一些這次不是重點關註的代碼，有興趣的可以自己去看下