Spring Boot(五)启动流程分析 – 仍是少年

学习过springboot的都知道,在Springboot的main入口函数中调用SpringApplication.run(DemoApplication.class,args)函数便可以启用SpringBoot应用程序,跟踪一下SpringApplication源码可以发现,最终还是调用了SpringApplication的动态run函数。

下面以SpringBoot2.0.3.RELEASE为例简单分析一下运行过程。

SpringApplicatiton部分源码:

1 public static ConfigurableApplicationContext run(Class<?>[] primarySources,
2       String[] args) {
3   //创建springapplication对象,调用函数run(args)
4    return new SpringApplication(primarySources).run(args);
5 }

上面的源码可以发现还是先创建SpringApplication实例,再调用run方法

第一步 分析 SpringApplication构造函数

SpringApplication构造函数代码如下:

 1  public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
 2    this.resourceLoader = resourceLoader;
 3    Assert.notNull(primarySources, "PrimarySources must not be null");
 4    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
 5 
 6   //1:判断web环境
 7    this.webApplicationType = deduceWebApplicationType();
 8 
 9   //2:加载classpath下META-INF/spring.factories中配置的ApplicationContextInitializer
10    setInitializers((Collection) getSpringFactoriesInstances(
11          ApplicationContextInitializer.class));
12   //3:加载classpath下META-INF/spring.factories中配置的ApplicationListener
13   
14    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
15   //4:推断main方法所在的类
16    this.mainApplicationClass = deduceMainApplicationClass();
17 }

具体逻辑分析:

  1. deduceWebApplicationType(),  SpringApplication构造函数中首先初始化应用类型,根据加载相关类路径判断应用类型,具体逻辑如下:
 1   private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework."
 2       + "web.reactive.DispatcherHandler";
 3 
 4   private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework."
 5       + "web.servlet.DispatcherServlet";
 6 
 7   private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
 8       "org.springframework.web.context.ConfigurableWebApplicationContext" };
 9 
10 
11 
12    private WebApplicationType deduceWebApplicationType() {
13   //当类路径中存在REACTIVE_WEB_ENVIRONMENT_CLASS并且不存在MVC_WEB_ENVIRONMENT_CLASS时
14    if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
15          && !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
16       return WebApplicationType.REACTIVE;
17    }
18   //当加载的类路径中不包含WEB_ENVIRONMENT_CLASSES中定义的任何一个类时,返回标准应用
19    for (String className : WEB_ENVIRONMENT_CLASSES) {
20       if (!ClassUtils.isPresent(className, null)) {22          return WebApplicationType.NONE;
23       }
24    }
25   //加载的类路径中包含了WEB_ENVIRONMENT_CLASSES中定义的所有类型则判断为web应用
26    return WebApplicationType.SERVLET;
27 }

  2. setInitializers初始化属性initializers,加载classpath下META-INF/spring.factories中配置的ApplicationContextInitializer,此处getSpringFactoriesInstances方法入参type=ApplicationContextInitializer.class

 1   private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
 2         Class<?>[] parameterTypes, Object... args) {
 3      ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
 4      // Use names and ensure unique to protect against duplicates
 5     // SpringFactoriesLoader.loadFactoryNames()方法将会从calssptah下的META-INF/spring.factories中读取key为//org.springframework.context.ApplicationContextInitializer的值,并以集合形式返回
 6      Set<String> names = new LinkedHashSet<>(
 7            SpringFactoriesLoader.loadFactoryNames(type, classLoader));
 8      //根据返回names集合逐个实例化,也就是初始化各种ApplicationContextInitializer,这些Initializer实际是在Spring上下文ApplicationContext执行refresh前调用
 9      List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
10          classLoader, args, names);
11      AnnotationAwareOrderComparator.sort(instances);
12      return instances;
13   }

       3. setListeners 初始化属性listeners,加载classpath下META-INF/spring.factories中配置的ApplicationListener,此处入参为getSpringFactoriesInstances方法入参type= ApplicationListener.class

 1    private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
 2         Class<?>[] parameterTypes, Object... args) {
 3      ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
 4      // Use names and ensure unique to protect against duplicates
 5     // SpringFactoriesLoader.loadFactoryNames()方法将会从calssptah下的META-INF/spring.factories中读取key为//org.springframework.context.ApplicationListener的值,并以集合形式返回
 6      Set<String> names = new LinkedHashSet<>(
 7          SpringFactoriesLoader.loadFactoryNames(type, classLoader));
 8     //根据配置,初始化各种ApplicationListener,作用是用来监听ApplicationEvent
 9      List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
10          classLoader, args, names);
11      AnnotationAwareOrderComparator.sort(instances);
12      return instances;
13   }

第二步 分析 SpringApplication中 run方法

SpringApplication的run方法代码如下:

 1 public ConfigurableApplicationContext run(String... args) {
 2    StopWatch stopWatch = new StopWatch();
 3    stopWatch.start();
 4    ConfigurableApplicationContext context = null;
 5    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
 6     //设置系统变量java.awt.headless
 7    configureHeadlessProperty();
 8     //1:加载classpath下面的META-INF/spring.factories SpringApplicationRunListener
 9    SpringApplicationRunListeners listeners = getRunListeners(args);
10     //2:执行所有runlistener的starting方法,实际上发布一个ApplicationStartingEvent事件
11    listeners.starting();
12    try {
13       //3:实例化ApplicationArguments对象
14       ApplicationArguments applicationArguments = new DefaultApplicationArguments(
15             args);
16       //4: 创建Environment (web环境 or 标准环境)+配置Environment,主要是把run方法的参数配置到Environment
17       ConfigurableEnvironment environment = prepareEnvironment(listeners,
18             applicationArguments);
19           configureIgnoreBeanInfo(environment);
20     //打印banner,SpringBoot启动时,控制台输出的一个歪歪扭扭的很不清楚的Spring几个大字母,也可以自定义,参考博客:http://majunwei.com/view/201708171646079868.html
21       Banner printedBanner = printBanner(environment);
22     //5: 根据不同environment实例化context
23       context = createApplicationContext();
24     // 异常处理
25       exceptionReporters = getSpringFactoriesInstances(
26             SpringBootExceptionReporter.class,
27             new Class[] { ConfigurableApplicationContext.class }, context);
28     //6: 上下文相关预处理
29       prepareContext(context, environment, listeners, applicationArguments,
30             printedBanner);
31     //7: 执行context的refresh,并且调用context的registerShutdownHook方法
32       refreshContext(context);
33     //8:空方法
34       afterRefresh(context, applicationArguments);
35       stopWatch.stop();
36       if (this.logStartupInfo) {
37          new StartupInfoLogger(this.mainApplicationClass)
38                .logStarted(getApplicationLog(), stopWatch);
39       }
40      //9:执行所有runlisteners的started方法,发布ApplicationStartedEvent事件
41       listeners.started(context);
42      //10: 遍历执行CommandLineRunner和ApplicationRunner
43      //如果需要在SpringBoot应用启动后运行一些特殊的逻辑,可以通过实现ApplicationRunner或CommandLineRunner接口中的run方法,该自定义类的run方法会在此处统一调用
44       callRunners(context, applicationArguments);
45    }
46    catch (Throwable ex) {
47       handleRunFailure(context, ex, exceptionReporters, listeners);
48       throw new IllegalStateException(ex);
49    }
50 
51    try {
52       listeners.running(context);
53    }
54    catch (Throwable ex) {
55       handleRunFailure(context, ex, exceptionReporters, null);
56       throw new IllegalStateException(ex);
57    }
58    return context;
59 }

具体分析:

  1. getRunListeners(args) 加载各种SpringApplicationRunListener实例,内部实现也还是通过SpringFactoriesLoader.loadFactoryNames(type, classLoader))实现,加载META-INF/spring.factories中key为org.springframework.boot.SpringApplicationRunListener的值,生成对应实例。

  2.  listeners.starting()  执行所有SpringApplicationRunListener的stating方法,发布ApplicationStartedEvent事件,该事件被ApplicationListener类型的listener监听

  3.  实例化ApplicationArguments对象

  4 . 配置环境并发布ApplicationEnvironmentPreparedEvent事件

 1    private ConfigurableEnvironment prepareEnvironment(
 2       SpringApplicationRunListeners listeners,
 3       ApplicationArguments applicationArguments) {
 4      // Create and configure the environment
 5    ConfigurableEnvironment environment = getOrCreateEnvironment();
 6   //configureEnvironment配置properties和profiles
 7    configureEnvironment(environment, applicationArguments.getSourceArgs());
 8   // 执行EventPublishingRunListener发布ApplicationEnvironmentPreparedEvent事件,将会被ApplicationListener监听到
 9    listeners.environmentPrepared(environment);
10   //
11    bindToSpringApplication(environment);
12    if (this.webApplicationType == WebApplicationType.NONE) {
13       environment = new EnvironmentConverter(getClassLoader())
14             .convertToStandardEnvironmentIfNecessary(environment);
15    }
16    ConfigurationPropertySources.attach(environment);
17    return environment;
18 }

备注:实际上载spring-boot-2.0.3.RELEASE.jar包中,可以发现spring.factories中只配置了一个RunListener: org.springframework.boot.context.event.EventPublishingRunListener

     截取EventPublishingRunListener.java部分代码:

 1 public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
 2     
 3 
 4      public EventPublishingRunListener(SpringApplication application, String[] args) {
 5        this.application = application;
 6        this.args = args;
 7        this.initialMulticaster = new SimpleApplicationEventMulticaster();
 8       //将SpringApplication实例中的ApplicationListener类型的listeners添加到initialMulticaster,后续执行监听
 9      for (ApplicationListener<?> listener : application.getListeners()) {
10         this.initialMulticaster.addApplicationListener(listener);
11      }
12   }
13 
14   // 发布一个ApplicationEnvironmentPreparedEvent事件
15     @Override
16     public void environmentPrepared(ConfigurableEnvironment environment) {
17         //所有被添加到initialMulticaster中的listener都将监听ApplicationEnvironmentPreparedEvent事件
18         this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
19                 this.application, this.args, environment));
20     }
21 
22 }

  5. 根据environment类型创建ApplicationContext

  6. 上下文相关处理:

 1 private void prepareContext(ConfigurableApplicationContext context,
 2       ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
 3       ApplicationArguments applicationArguments, Banner printedBanner) {
 4    context.setEnvironment(environment);
 5   //配置beanNameGenerator和资源加载器
 6    postProcessApplicationContext(context);
 7   //回调所有的ApplicationContextInitializer
 8    applyInitializers(context);
 9   //执行所有SpringApplicationRunListener的contextPrepared方法,触发事件,实际上EventPublishingRunListener中contextPrepared是一个空方法,什么都没执行
10    listeners.contextPrepared(context);
11    if (this.logStartupInfo) {
12       logStartupInfo(context.getParent() == null);
13       logStartupProfileInfo(context);
14    }
15 
16   //向Spring容器注入springApplicationArguments和springBootBanner
17    // Add boot specific singleton beans
18    context.getBeanFactory().registerSingleton("springApplicationArguments",
19          applicationArguments);
20    if (printedBanner != null) {
21       context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
22    }
23 
24    // Load the sources
25    Set<Object> sources = getAllSources();
26    Assert.notEmpty(sources, "Sources must not be empty");
27    load(context, sources.toArray(new Object[0]));
28   //执行所有SpringApplicationRunListener的contextLoaded方法,下面是EventPublishingRunListener中的contextLoaded
29    listeners.contextLoaded(context);
30 }

EventPublishingRunListener.java中contextLoaded方法具体实现

 1 public void contextLoaded(ConfigurableApplicationContext context) {
 2    for (ApplicationListener<?> listener : this.application.getListeners()) {
 3       if (listener instanceof ApplicationContextAware) {
 4          ((ApplicationContextAware) listener).setApplicationContext(context);
 5       }
 6       context.addApplicationListener(listener);
 7    }
 8   //触发ApplicationPreparedEvent事件,ApplicationListener负责监听
 9    this.initialMulticaster.multicastEvent(
10          new ApplicationPreparedEvent(this.application, this.args, context));
11 }

  7.  执行context的refresh,并且调用context的registerShutdownHook方法

  8. afterRefresh空方法

  9. 执行所有runlisteners的started方法,发布ApplicationStartedEvent事件

  10. 遍历执行CommandLineRunner和ApplicationRunner

以上。

 



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