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SpringBoot啟動(dòng)流程SpringApplication準(zhǔn)備階段源碼分析

 更新時(shí)間：2023年04月03日 14:01:01   作者：唐小碼  
這篇文章主要為大家介紹了SpringBoot啟動(dòng)流程SpringApplication準(zhǔn)備階段源碼分析，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪

SpringBoot啟動(dòng)流程源碼分析一、入口參數(shù)研究和創(chuàng)建對(duì)象

我們?cè)谏弦黄臅r(shí)候主要針對(duì)入口參數(shù)和SpringApplication創(chuàng)建對(duì)象的過(guò)程進(jìn)行了研究，本篇主要針對(duì)執(zhí)行run方法之前的準(zhǔn)備過(guò)程進(jìn)行研究。

準(zhǔn)備階段分析

以下先看下SpringApplication的run()方法

package org.springframework.boot;
public ConfigurableApplicationContext run(String... args) {
   //1.計(jì)時(shí)器
   StopWatch stopWatch = new StopWatch();
   stopWatch.start();
   ConfigurableApplicationContext context = null;
   Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
   //2.headless配置
   configureHeadlessProperty();
   //3、獲取監(jiān)聽(tīng)
   SpringApplicationRunListeners listeners = getRunListeners(args);
   listeners.starting();
   try {
   //應(yīng)用程序啟動(dòng)的參數(shù)  
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      //4、準(zhǔn)備環(huán)境
      ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
      //環(huán)境創(chuàng)建成功后，配置bean信息，決定是否跳過(guò) BeanInfo 類的掃描，如果設(shè)置為 true,則跳過(guò)
      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);
      //停止計(jì)時(shí)
      stopWatch.stop();
      //控制是否打印日志的,這里為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;
}

我將會(huì)根據(jù)執(zhí)行過(guò)程逐行進(jìn)行分析

1、StopWatch計(jì)時(shí)器

此類實(shí)則為計(jì)時(shí)器，如下對(duì)具體使用進(jìn)行分析

StopWatch stopWatch = new StopWatch();
//開始計(jì)時(shí)
stopWatch.start();
//停止計(jì)時(shí)
stopWatch.stop();

對(duì)于具體打印的上面寫的為

//將當(dāng)前類傳入StartupInfoLogger創(chuàng)建了一個(gè)對(duì)象
//然后調(diào)用logStarted打印日志
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
//創(chuàng)建一個(gè)Log類
protected Log getApplicationLog() {
   if (this.mainApplicationClass == null) {
      return logger;
   }
   return LogFactory.getLog(this.mainApplicationClass);
}
//調(diào)用log類的log.info()方法來(lái)打印日志
public void logStarted(Log log, StopWatch stopWatch) {
    if (log.isInfoEnabled()) {
            log.info(getStartedMessage(stopWatch));
    }
}
//打印詳細(xì)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;
}

這里可以看到stopWatch.getTotalTimeSeconds()方法就是來(lái)獲取實(shí)際的計(jì)時(shí)時(shí)間的。再者，通過(guò)這幾行代碼，我們也可以考慮下平常在寫代碼的時(shí)候，有幾種日志打印方式？SpringBoot是怎么集成日志框架的？

2、configureHeadlessProperty()

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)));
}

這一部分代碼這樣理解吧，首先java.awt包提供了用于創(chuàng)建用戶界面和繪制圖形圖像的所有分類,那么 屬性SYSTEM_PROPERTY_JAVA_AWT_HEADLESS就一定會(huì)和用戶界面相關(guān)了。 這里將SYSTEM_PROPERTY_JAVA_AWT_HEADLESS設(shè)置為true，其實(shí)就是表示在缺少顯示屏、鍵盤或者鼠標(biāo)中的系統(tǒng)配置，如果將其設(shè)置為true，那么headless工具包就會(huì)被使用。

3、getRunListeners(args) 獲取監(jiān)聽(tīng)

總體上可以分這三步

  • 獲取一個(gè)默認(rèn)的加載器
  • 根據(jù)類型獲取spring.factories中符合的類名
  • 創(chuàng)建類實(shí)例，返回

如下將跟下代碼

//獲取所有監(jiān)聽(tīng)
SpringApplicationRunListeners listeners = getRunListeners(args);
//啟動(dòng)監(jiān)聽(tīng)
listeners.starting();

跳轉(zhuǎn)進(jìn)入getRunListeners方法

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獲取類加載器
   ClassLoader classLoader = getClassLoader();
   // Use names and ensure unique to protect against duplicates
   //3.2 根據(jù)類型獲取spring.factories中符合的類名
   Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
   //3.3 創(chuàng)建類實(shí)例
   List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
   //對(duì)實(shí)例進(jìn)行排序
   AnnotationAwareOrderComparator.sort(instances);
   return instances;
}

SpringApplicationRunListeners類解讀

先看下SpringApplicationRunListeners類

/**
 * A collection of {@link SpringApplicationRunListener}.
 *
 * @author Phillip Webb
 */
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);
   }

SpringApplicationRunListeners類內(nèi)部關(guān)聯(lián)了SpringApplicationRunListener的集合，說(shuō)白了就是用List集合存儲(chǔ)了SpringApplicationRunListeners類，那么，我們就需要了解一下這個(gè)類是干嘛的

老規(guī)矩，先把源碼抬上來(lái)

/**
 *//可以理解為Spring Boot應(yīng)用的運(yùn)行時(shí)監(jiān)聽(tīng)器
 * Listener for the {@link SpringApplication} {@code run} method.
 *//SpringApplicationRunListener的構(gòu)造器參數(shù)必須依次為SpringApplication和String[]類型
 * {@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.
 *//每次運(yùn)行的時(shí)候?qū)?huì)創(chuàng)建一個(gè) SpringApplicationRunListener
  A new
 * {@link SpringApplicationRunListener} instance will be created for each run.
 *
 */
public interface SpringApplicationRunListener {
   /**
    * Called immediately when the run method has first started. Can be used for very
    * early initialization.
    */
    //Spring應(yīng)用剛啟動(dòng)
   void starting();
   /**
    * Called once the environment has been prepared, but before the
    * {@link ApplicationContext} has been created.
    * @param environment the environment
    */
    //ConfigurableEnvironment準(zhǔn)備妥當(dāng)，允許將其調(diào)整
   void environmentPrepared(ConfigurableEnvironment environment);
   /**
    * Called once the {@link ApplicationContext} has been created and prepared, but
    * before sources have been loaded.
    * @param context the application context
    */
    //ConfigurableApplicationContext準(zhǔn)備妥當(dāng)，允許將其調(diào)整
   void contextPrepared(ConfigurableApplicationContext context);
   /**
    * Called once the application context has been loaded but before it has been
    * refreshed.
    * @param context the application context
    */
    //ConfigurableApplicationContext已裝載，但是任未啟動(dòng)
   void contextLoaded(ConfigurableApplicationContext context);
   /**
    * The context has been refreshed and the application has started but
    * {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
    * ApplicationRunners} have not been called.
    * @param context the application context.
    * @since 2.0.0
    */
    //ConfigurableApplicationContext已啟動(dòng)，此時(shí)Spring Bean已初始化完成
   void started(ConfigurableApplicationContext context);
   /**
    * Called immediately before the run method finishes, when the application context has
    * been refreshed and all {@link CommandLineRunner CommandLineRunners} and
    * {@link ApplicationRunner ApplicationRunners} have been called.
    * @param context the application context.
    * @since 2.0.0
    */
    //Spring應(yīng)用正在運(yùn)行
   void running(ConfigurableApplicationContext context);
   /**
    * Called when a failure occurs when running the application.
    * @param context the application context or {@code null} if a failure occurred before
    * the context was created
    * @param exception the failure
    * @since 2.0.0
    */
    //Spring應(yīng)用運(yùn)行失敗
   void failed(ConfigurableApplicationContext context, Throwable exception);
}

單純的看源碼，是一個(gè)簡(jiǎn)單的接口，這時(shí)候我們可以看下作者給的注釋。理解部分就直接加到上面源碼中了。

再看下他的實(shí)現(xiàn)類EventPublishingRunListener

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);
      }
   }

這里我們看到兩點(diǎn)：

  • 構(gòu)造器參數(shù)和他實(shí)現(xiàn)的接口（上面剛分析了）注釋中規(guī)定的一致
  • 將SpringApplication中的ApplicationListener實(shí)例列表全部添加到了SimpleApplicationEventMulticaster對(duì)象中

SimpleApplicationEventMulticaster是Spring框架的一個(gè)監(jiān)聽(tīng)類，用于發(fā)布Spring應(yīng)用事件。因此EventPublishingRunListener實(shí)際充當(dāng)了Spring Boot事件發(fā)布者的角色。

這里我再跟進(jìn)源碼的時(shí)候發(fā)現(xiàn)，針對(duì)SpringBoot的事件/監(jiān)聽(tīng)機(jī)制內(nèi)容還是挺多的，我們?cè)诔浞掷斫獾臅r(shí)候需要先了解Spring的事件/監(jiān)聽(tīng)機(jī)制，后面將兩個(gè)結(jié)合后單獨(dú)進(jìn)行對(duì)比分析。

3.1獲取類加載器getClassLoader()

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

這里的類加載器獲取首先是獲取resourceLoader的類加載器，獲取不到則獲取默認(rèn)的類加載器。 resourceLoader是資源加載器類，有具體的實(shí)現(xiàn)類。

3.2 根據(jù)類型獲取spring.factories中符合的類名

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

我們繼續(xù)對(duì)loadSpringFactories追下去

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
    //從緩存里面獲取
    MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
    if (result != null) {
        return result;
    } else {
        try {
        //執(zhí)行classLoader.getResources("META-INF/spring.factories")，表示通過(guò)加載器獲取META-INF/spring.factories下的資源
            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();
                //從指定位置加載UrlResource
                UrlResource resource = new UrlResource(url);
                //加載里面的屬性，屬性見(jiàn)下圖
                Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                Iterator var6 = properties.entrySet().iterator();
                while(var6.hasNext()) {
                    Entry<?, ?> entry = (Entry)var6.next();
                    //獲取key值
                    String factoryClassName = ((String)entry.getKey()).trim();
                    //獲取value值
                    String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                    int var10 = var9.length;
//這里是將查詢出來(lái)的key作為result的key,value轉(zhuǎn)換成字符數(shù)組存放到result的value中
                    for(int var11 = 0; var11 < var10; ++var11) {
                        String factoryName = var9[var11];
                        result.add(factoryClassName, factoryName.trim());
                    }
                }
            }
            //將結(jié)果集存入緩存中
            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;
}

這個(gè)的意思是如果沒(méi)有，則獲取一個(gè)空的list

3.3創(chuàng)建實(shí)例createSpringFactoriesInstances()

這一步其實(shí)就是將上一步從META-INF/spring.factories加載進(jìn)來(lái)的資源進(jìn)行實(shí)例化。

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 {
      //根據(jù)類加載器獲取指定類
         Class<?> instanceClass = ClassUtils.forName(name, classLoader);
         Assert.isAssignable(type, instanceClass);
         //根據(jù)參數(shù)獲取構(gòu)造器
         Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
         //根據(jù)傳入的構(gòu)造器對(duì)象以及構(gòu)造器所需的參數(shù)創(chuàng)建一個(gè)實(shí)例
         T instance = (T) BeanUtils.instantiateClass(constructor, args);
         //添加實(shí)例到集合中
         instances.add(instance);
      }
      catch (Throwable ex) {
         throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
      }
   }
   return instances;
}

4、環(huán)境準(zhǔn)備prepareEnvironment

prepareEnvironment(listeners, applicationArguments)

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
      ApplicationArguments applicationArguments) {
   // Create and configure the environment
   //4.1 創(chuàng)建一個(gè)環(huán)境
   ConfigurableEnvironment environment = getOrCreateEnvironment();
   //4.2 配置環(huán)境
   configureEnvironment(environment, applicationArguments.getSourceArgs());
   //4.3 ConfigurationPropertySourcesPropertySource對(duì)象存入到第一位
   ConfigurationPropertySources.attach(environment);
   //listeners環(huán)境準(zhǔn)備(就是廣播ApplicationEnvironmentPreparedEvent事件)
   listeners.environmentPrepared(environment);
   // 將環(huán)境綁定到SpringApplication
   bindToSpringApplication(environment);
     // 如果是非web環(huán)境，將環(huán)境轉(zhuǎn)換成StandardEnvironment
   if (!this.isCustomEnvironment) {
      environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
            deduceEnvironmentClass());
   }
    // 配置PropertySources對(duì)它自己的遞歸依賴
   ConfigurationPropertySources.attach(environment);
   return environment;
}

4.1創(chuàng)建一個(gè)環(huán)境getOrCreateEnvironment

private ConfigurableEnvironment getOrCreateEnvironment() {
//有的話，直接返回
  if (this.environment != null) {
     return this.environment;
  }
  //這里我們?cè)谏厦嬉?jiàn)到過(guò)，通過(guò)WebApplicationType.deduceFromClasspath()方法獲取的
  switch (this.webApplicationType) {
  case SERVLET:
     return new StandardServletEnvironment();
  case REACTIVE:
     return new StandardReactiveWebEnvironment();
  default:
     return new StandardEnvironment();
  }
}

這里創(chuàng)建了一個(gè)StandardServletEnvironment實(shí)例的環(huán)境 systemProperties用來(lái)封裝了JDK相關(guān)的信息 如下圖

systemEnvironment用來(lái)封轉(zhuǎn)環(huán)境相關(guān)的信息

封裝的還是挺詳細(xì)的哈。

4.2 配置環(huán)境

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

setConversionService(ConfigurableConversionService conversionService)方法繼承于ConfigurablePropertyResolver接口， 該接口是PropertyResolver類型都將實(shí)現(xiàn)的配置接口。提供用于訪問(wèn)和自定義將屬性值從一種類型轉(zhuǎn)換為另一種類型時(shí)使用的ConversionService的工具。PropertyResolver是用于針對(duì)任何底層源解析屬性的接口。

configurePropertySources(environment, args);當(dāng)前方法主要是將啟動(dòng)命令中的參數(shù)和run 方法中的參數(shù)封裝為PropertySource。

protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
//獲取所有的屬性源，就是獲取4.1的ConfigurableEnvironment上獲取到的屬性
  MutablePropertySources sources = environment.getPropertySources();
  if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
     sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
  }
  //是否添加命令啟動(dòng)參數(shù)，addCommandLineProperties為true，表示需要添加，但是前提是你得配置了參數(shù)
  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));
     }
  }
}

configureProfiles(environment, args);環(huán)境配置

protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
//獲取激活的環(huán)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()));
  //設(shè)置當(dāng)前的環(huán)境
  environment.setActiveProfiles(StringUtils.toStringArray(profiles));
}

4.3 ConfigurationPropertySourcesPropertySource對(duì)象存入

public static void attach(Environment environment) {
   Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
   //獲取所有的屬性源，就是獲取4.1的ConfigurableEnvironment上獲取到的屬性
   MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
   //判斷是否有 屬性 configurationProperties
   PropertySource&lt;?&gt; attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
   if (attached != null &amp;&amp; attached.getSource() != sources) {
      sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
      attached = null;
   }
   if (attached == null) {
   // 將sources封裝成ConfigurationPropertySourcesPropertySource對(duì)象，并把這個(gè)對(duì)象放到sources的第一位置
      sources.addFirst(new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
            new SpringConfigurationPropertySources(sources)));
   }
}

總結(jié)

準(zhǔn)備階段主要干了如下幾件事情

  • 設(shè)置headless為true（表示可以在缺少顯示屏、鍵盤或者鼠標(biāo)時(shí)候的系統(tǒng)配置）
  • 文件META-INF\spring.factories中獲取SpringApplicationRunListener接口的實(shí)現(xiàn)類EventPublishingRunListener，主要發(fā)布SpringApplicationEvent。
  • 創(chuàng)建Environment并設(shè)置比如環(huán)境信息，系統(tǒng)屬性，輸入?yún)?shù)和profile等信息
  • 打印Banner信息

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參考：《SpringBoot編程思想》

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