SprintBoot 2 源码阅读

先上菜单，核心方法

    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();
        ConfigurableApplicationContext context = null;
        this.configureHeadlessProperty();
        // 获取监听器
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        // 启动监听
        listeners.starting(bootstrapContext, this.mainApplicationClass);

        Throwable ex;
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            // 创建 容器
            context = this.createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
            // 准备容器
            this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
            // 刷新容器
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            ex = var10;
            this.handleRunFailure(context, ex, listeners);
            throw new IllegalStateException(ex);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            ex = var9;
            this.handleRunFailure(context, ex, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(ex);
        }
    }

先来看看怎么获取监听器

SpringApplicationRunListeners listeners = this.getRunListeners(args);


private SpringApplicationRunListeners getRunListeners(String[] args) {
        Class<?>[] types = new Class[]{SpringApplication.class, String[].class};
        return new SpringApplicationRunListeners(logger, this.getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args), this.applicationStartup);
    }

  private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
        ClassLoader classLoader = this.getClassLoader();
        Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
        List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
        AnnotationAwareOrderComparator.sort(instances);
        return instances;
    }


  public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
        ClassLoader classLoaderToUse = classLoader;
        if (classLoaderToUse == null) {
            classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
        }

        String factoryTypeName = factoryType.getName();
        return (List)loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
    }


    // 核心
    private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
        Map<String, List<String>> result = (Map)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            Map<String, List<String>> result = new HashMap();

            try {
                Enumeration<URL> urls = classLoader.getResources("META-INF/spring.factories");

                while(urls.hasMoreElements()) {
                    URL url = (URL)urls.nextElement();
                    UrlResource resource = new UrlResource(url);
                    Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                    Iterator var6 = properties.entrySet().iterator();

                    while(var6.hasNext()) {
                        Map.Entry<?, ?> entry = (Map.Entry)var6.next();
                        String factoryTypeName = ((String)entry.getKey()).trim();
                        String[] factoryImplementationNames = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                        String[] var10 = factoryImplementationNames;
                        int var11 = factoryImplementationNames.length;

                        for(int var12 = 0; var12 < var11; ++var12) {
                            String factoryImplementationName = var10[var12];
                            ((List)result.computeIfAbsent(factoryTypeName, (key) -> {
                                return new ArrayList();
                            })).add(factoryImplementationName.trim());
                        }
                    }
                }

                result.replaceAll((factoryType, implementations) -> {
                    return (List)implementations.stream().distinct().collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
                });
                cache.put(classLoader, result);
                return result;
            } catch (IOException var14) {
                IOException ex = var14;
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", ex);
            }
        }
    }

        //获取到META-INF/spring.factories这个配置文件下的资源名称列表以后，通过createSpringFactoriesInstances函数创建了SpringFactories的实例。
        private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) {
        List<T> instances = new ArrayList(names.size());
        Iterator var7 = names.iterator();

        while(var7.hasNext()) {
            String name = (String)var7.next();

            try {
                Class<?> instanceClass = ClassUtils.forName(name, classLoader);
                Assert.isAssignable(type, instanceClass);
                Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
                T instance = BeanUtils.instantiateClass(constructor, args);
                instances.add(instance);
            } catch (Throwable var12) {
                Throwable ex = var12;
                throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
            }
        }

        return instances;
    }

加载这个目录下面的所有类，然后找到监听器

再看启动监听器做了什么，我们先大概地看一下EventPublishingRunListener里面的starting的实现

 listeners.starting(bootstrapContext, this.mainApplicationClass);

   public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);
        Executor executor = this.getTaskExecutor();
        Iterator var5 = this.getApplicationListeners(event, type).iterator();

        while(var5.hasNext()) {
            ApplicationListener<?> listener = (ApplicationListener)var5.next();
            if (executor != null) {
                executor.execute(() -> {
                    this.invokeListener(listener, event);
                });
            } else {
                this.invokeListener(listener, event);
            }
        }

    }

    
  protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
        ErrorHandler errorHandler = this.getErrorHandler();
        if (errorHandler != null) {
            try {
                this.doInvokeListener(listener, event);
            } catch (Throwable var5) {
                Throwable err = var5;
                errorHandler.handleError(err);
            }
        } else {
            this.doInvokeListener(listener, event);
        }

    }

在上面代码中我们看到，starting就是拿到META-INF/spring.factories中定义的资源的实例以后，然后再创建一个线程去启动起来**。**