SpringBoot启动流程SpringApplication准备阶段源码分析

package org.springframework.boot;
public ConfigurableApplicationContext run(String... args) {
   //1.计时器
   StopWatch stopWatch = new StopWatch();
   stopWatch.start();
   ConfigurableApplicationContext context = null;
   Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
   //2.headless配置
   configureHeadlessProperty();
   //3、获取监听
   SpringApplicationRunListeners listeners = getRunListeners(args);
   listeners.starting();
   try {
   //应用程序启动的参数  
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      //4、准备环境
      ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
      //环境创建成功后，配置bean信息，决定是否跳过 BeanInfo 类的扫描，如果设置为 true,则跳过
      configureIgnoreBeanInfo(environment);
      //打印banner信息
      Banner printedBanner = printBanner(environment);
      context = createApplicationContext();
      exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
            new Class[] { ConfigurableApplicationContext.class }, context);
      prepareContext(context, environment, listeners, applicationArguments, printedBanner);
      refreshContext(context);
      afterRefresh(context, applicationArguments);
      //停止计时
      stopWatch.stop();
      //控制是否打印日志的,这里为true，即打印日志
      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;
}

StopWatch stopWatch = new StopWatch();
//开始计时
stopWatch.start();
//停止计时
stopWatch.stop();

//将当前类传入StartupInfoLogger创建了一个对象
//然后调用logStarted打印日志
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
//创建一个Log类
protected Log getApplicationLog() {
   if (this.mainApplicationClass == null) {
      return logger;
   }
   return LogFactory.getLog(this.mainApplicationClass);
}
//调用log类的log.info()方法来打印日志
public void logStarted(Log log, StopWatch stopWatch) {
    if (log.isInfoEnabled()) {
            log.info(getStartedMessage(stopWatch));
    }
}
//打印详细的日志
private StringBuilder getStartedMessage(StopWatch stopWatch) {
   StringBuilder message = new StringBuilder();
   message.append("Started ");
   message.append(getApplicationName());
   message.append(" in ");
   message.append(stopWatch.getTotalTimeSeconds());
   try {
      double uptime = ManagementFactory.getRuntimeMXBean().getUptime() / 1000.0;
      message.append(" seconds (JVM running for " + uptime + ")");
   }
   catch (Throwable ex) {
      // No JVM time available
   }
   return message;
}

private static final String SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";
private void configureHeadlessProperty() {
   System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS,
         System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
}

//获取所有监听
SpringApplicationRunListeners listeners = getRunListeners(args);
//启动监听
listeners.starting();

private SpringApplicationRunListeners getRunListeners(String[] args) {
   Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
   return new SpringApplicationRunListeners(logger,
         getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
  //3.1获取类加载器
   ClassLoader classLoader = getClassLoader();
   // Use names and ensure unique to protect against duplicates
   //3.2 根据类型获取spring.factories中符合的类名
   Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
   //3.3 创建类实例
   List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
   //对实例进行排序
   AnnotationAwareOrderComparator.sort(instances);
   return instances;
}

class SpringApplicationRunListeners {
   private final Log log;
   private final List<SpringApplicationRunListener> listeners;
   SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {
      this.log = log;
      this.listeners = new ArrayList<>(listeners);
   }

/可以理解为Spring Boot应用的运行时监听器
 * Listener for the {@link SpringApplication} {@code run} method.
 *//SpringApplicationRunListener的构造器参数必须依次为SpringApplication和String[]类型
 * {@link SpringApplicationRunListener}s are loaded via the {@link SpringFactoriesLoader}
 * and should declare a public constructor that accepts a {@link SpringApplication}
 * instance and a {@code String[]} of arguments.
 *//每次运行的时候将会创建一个 SpringApplicationRunListener
  A new
 * {@link SpringApplicationRunListener} instance will be created for each run.
 *
 */
public interface SpringApplicationRunListener {
   
    //Spring应用刚启动
   void starting();
   
    //ConfigurableEnvironment准备妥当，允许将其调整
   void environmentPrepared(ConfigurableEnvironment environment);
   
    //ConfigurableApplicationContext准备妥当，允许将其调整
   void contextPrepared(ConfigurableApplicationContext context);
   
    //ConfigurableApplicationContext已装载，但是任未启动
   void contextLoaded(ConfigurableApplicationContext context);
   
    //ConfigurableApplicationContext已启动，此时Spring Bean已初始化完成
   void started(ConfigurableApplicationContext context);
   
    //Spring应用正在运行
   void running(ConfigurableApplicationContext context);
   
    //Spring应用运行失败
   void failed(ConfigurableApplicationContext context, Throwable exception);
}

public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
   private final SpringApplication application;
   private final String[] args;
   private final SimpleApplicationEventMulticaster initialMulticaster;
   public EventPublishingRunListener(SpringApplication application, String[] args) {
      this.application = application;
      this.args = args;
      this.initialMulticaster = new SimpleApplicationEventMulticaster();
      for (ApplicationListener<?> listener : application.getListeners()) {
         this.initialMulticaster.addApplicationListener(listener);
      }
   }

ClassLoader classLoader = getClassLoader();
public ClassLoader getClassLoader() {
  if (this.resourceLoader != null) {
     return this.resourceLoader.getClassLoader();
  }
  return ClassUtils.getDefaultClassLoader();
}

SpringFactoriesLoader.loadFactoryNames(type, classLoader)
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
//获取类型名称：org.springframework.context.ApplicationContextInitializer
   String factoryClassName = factoryClass.getName();
   return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
    //从缓存里面获取
    MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
    if (result != null) {
        return result;
    } else {
        try {
        //执行classLoader.getResources("META-INF/spring.factories")，表示通过加载器获取META-INF/spring.factories下的资源
            Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
            LinkedMultiValueMap result = new LinkedMultiValueMap();
            while(urls.hasMoreElements()) {
               //文件地址
                URL url = (URL)urls.nextElement();
                //从指定位置加载UrlResource
                UrlResource resource = new UrlResource(url);
                //加载里面的属性，属性见下图
                Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                Iterator var6 = properties.entrySet().iterator();
                while(var6.hasNext()) {
                    Entry<?, ?> entry = (Entry)var6.next();
                    //获取key值
                    String factoryClassName = ((String)entry.geTKEy()).trim();
                    //获取value值
                    String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                    int var10 = var9.length;
//这里是将查询出来的key作为result的key,value转换成字符数组存放到result的value中
                    for(int var11 = 0; var11 < var10; ++var11) {
                        String factoryName = var9[var11];
                        result.add(factoryClassName, factoryName.trim());
                    }
                }
            }
            //将结果集存入缓存中
            cache.put(classLoader, result);
            return result;
        } catch (IOException var13) {
            throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
        }
    }
}

default V getOrDefault(Object key, V defaultValue) {
    V v;
    return (((v = get(key)) != null) || containsKey(key))
        ? v
        : defaultValue;
}

private <T> List<T> createSpringFactoriesInstances()(Class<T> type, Class<?>[] parameterTypes,
      ClassLoader classLoader, Object[] args, Set<String> names) {
   List<T> instances = new ArrayList<>(names.size());
   for (String name : names) {
      try {
      //根据类加载器获取指定类
         Class<?> instanceClass = ClassUtils.forName(name, classLoader);
         Assert.isAssignable(type, instanceClass);
         //根据参数获取构造器
         Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
         //根据传入的构造器对象以及构造器所需的参数创建一个实例
         T instance = (T) BeanUtils.instantiateClass(constructor, args);
         //添加实例到集合中
         instances.add(instance);
      }
      catch (Throwable ex) {
         throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
      }
   }
   return instances;
}

prepareEnvironment(listeners, applicationArguments)

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
      ApplicationArguments applicationArguments) {
   // Create and configure the environment
   //4.1 创建一个环境
   ConfigurableEnvironment environment = getOrCreateEnvironment();
   //4.2 配置环境
   configureEnvironment(environment, applicationArguments.getSourceArgs());
   //4.3 ConfigurationPropertySourcesPropertySource对象存入到第一位
   ConfigurationPropertySources.attach(environment);
   //listeners环境准备(就是广播ApplicationEnvironmentPreparedEvent事件)
   listeners.environmentPrepared(environment);
   // 将环境绑定到SpringApplication
   bindToSpringApplication(environment);
     // 如果是非WEB环境，将环境转换成StandardEnvironment
   if (!this.isCustomEnvironment) {
      environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
            deduceEnvironmentClass());
   }
    // 配置PropertySources对它自己的递归依赖
   ConfigurationPropertySources.attach(environment);
   return environment;
}

private ConfigurableEnvironment getOrCreateEnvironment() {
//有的话，直接返回
  if (this.environment != null) {
     return this.environment;
  }
  //这里我们在上面见到过，通过WebApplicationType.deduceFromClasspath()方法获取的
  switch (this.webApplicationType) {
  case SERVLET:
     return new StandardServletEnvironment();
  case ReactIVE:
     return new StandardReactiveWebEnvironment();
  default:
     return new StandardEnvironment();
  }
}

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
   if (this.addConversionService) {
      ConversionService conversionService = ApplicationConversionService.getSharedInstance();
      environment.setConversionService((ConfigurableConversionService) conversionService);
   }
   configurePropertySources(environment, args);
   configureProfiles(environment, args);
}

protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
//获取所有的属性源，就是获取4.1的ConfigurableEnvironment上获取到的属性
  MutablePropertySources sources = environment.getPropertySources();
  if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
     sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
  }
  //是否添加命令启动参数，addCommandLineProperties为true，表示需要添加，但是前提是你得配置了参数
  if (this.addCommandLineProperties && args.length > 0) {
     String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
     if (sources.contains(name)) {
        PropertySource<?> source = sources.get(name);
        CompositePropertySource composite = new CompositePropertySource(name);
        composite.addPropertySource(
              new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
        composite.addPropertySource(source);
        sources.replace(name, composite);
     }
     else {
        sources.addFirst(new SimpleCommandLinePropertySource(args));
     }
  }
}

protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
//获取激活的环境
  environment.getActiveProfiles(); // ensure they are initialized
  // But these ones should Go first (last wins in a property key clash)
  Set<String> profiles = new LinkedHashSet<>(this.additionalProfiles);
  profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
  //设置当前的环境
  environment.setActiveProfiles(StringUtils.toStringArray(profiles));
}

public static void attach(Environment environment) {
   Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
   //获取所有的属性源，就是获取4.1的ConfigurableEnvironment上获取到的属性
   MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
   //判断是否有 属性 configurationProperties
   PropertySource<?> attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
   if (attached != null && attached.getSource() != sources) {
      sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
      attached = null;
   }
   if (attached == null) {
   // 将sources封装成ConfigurationPropertySourcesPropertySource对象，并把这个对象放到sources的第一位置
      sources.addFirst(new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
            new SprinGConfigurationPropertySources(sources)));
   }
}