王尘宇

这些就是框架定义的，需要装配的类。

application.yml的加载

application.yml文件对于 Spring Boot 来说是核心配置文件，至关重要！那么，该文件是如何加载到内存的呢？我们需要从启动类的run()方法开始跟踪，该跟踪过程比较深，耐心差的读者慎入。

@SpringBootApplication
public class SpringbootSeniorApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootSeniorApplication.class, args);
    }
}

进入run方法：

public class SpringApplication {
    ...
    public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
        return run(new Class<?>[] { primarySource }, args);
    }

    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
        return new SpringApplication(primarySources).run(args);
    }

    public ConfigurableApplicationContext run(String... args) {
        ...
        // 准备运行环境
        ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
        ...
    }

    private ConfigurableEnvironment prepareEnvironment(
            SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments) {
        ...
        // 让监听器监听环境准备过程
        listeners.environmentPrepared(environment);
        ...
    }
    ...
}

让监听器监听环境准备过程

class SpringApplicationRunListeners {
    ...
    void environmentPrepared(ConfigurableEnvironment environment) {
        for (SpringApplicationRunListener listener : this.listeners) {
            listener.environmentPrepared(environment);
        }
    }
    ...
}

发布环境准备事件

public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
    ...
    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        this.initialMulticaster.multicastEvent(
            new ApplicationEnvironmentPreparedEvent(
                this.application,
                this.args,
                environment
            )
        );
    }

    @Override
    public void multicastEvent(ApplicationEvent event) {
        multicastEvent(event, resolveDefaultEventType(event));
    }

    @Override
    public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        Executor executor = getTaskExecutor();
        for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            if (executor != null) {
                // 触发监听器
                executor.execute(() -> invokeListener(listener, event));
            }
            else {
                invokeListener(listener, event);
            }
        }
    }
    ...
}

触发监听器

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

    private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
        ...
        listener.onApplicationEvent(event);
        ...
    }
    ...
}

ApplicationListener#onApplicationEvent是一个接口方法，我们主要看它的ConfigFileApplicationListener实现类的实现

public class ConfigFileApplicationListener implements ... {
    ...
    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
        }
        ...
    }

    private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
        List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
        postProcessors.add(this);
        AnnotationAwareOrderComparator.sort(postProcessors);
        for (EnvironmentPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication());
        }
    }
    ...
}

EnvironmentPostProcessor#postProcessEnvironment是一个接口方法，我们主要看它的ConfigFileApplicationListener实现类的实现

public class ConfigFileApplicationListener implements ... {
    ...
    @Override
    public void postProcessEnvironment(
            ConfigurableEnvironment environment,
            SpringApplication application) {
        // 加载配置文件
        addPropertySources(environment, application.getResourceLoader());
    }

    protected void addPropertySources(
            ConfigurableEnvironment environment,
            ResourceLoader resourceLoader) {
        RandomValuePropertySource.addToEnvironment(environment);
        new Loader(environment, resourceLoader).load();
    }

    private class Loader {
        void load() {
            FilteredPropertySource.apply(
                this.environment, 
                DEFAULT_PROPERTIES, 
                LOAD_FILTERED_PROPERTY,
                (defaultProperties) -> {
                    ...
                    while (!this.profiles.isEmpty()) {
                        ...
                        load(profile, this::getPositiveProfileFilter,
                                addToLoaded(MutablePropertySources::addLast, false));
                        ...
                    }
                    ...
                });
        }

        private void load(Profile profile, DocumentFilterFactory filterFactory, DocumentConsumer consumer) {
            getSearchLocations().forEach((location) -> {
                boolean isDirectory = location.endsWith("/");
                Set<String> names = isDirectory ? getSearchNames() : NO_SEARCH_NAMES;
                names.forEach((name) -> load(location, name, profile, filterFactory, consumer));
            });
        }

        private void load(String location, String name, Profile profile, DocumentFilterFactory filterFactory,
                DocumentConsumer consumer) {
            ...
            for (PropertySourceLoader loader : this.propertySourceLoaders) {
                for (String fileExtension : loader.getFileExtensions()) {
                    if (processed.add(fileExtension)) {
                        loadForFileExtension(loader, location + name, "." + fileExtension, profile, filterFactory, consumer);
                    }
                }
            }
        }

        private void loadForFileExtension(
                PropertySourceLoader loader,
                String prefix,
                String fileExtension,
                Profile profile,
                DocumentFilterFactory filterFactory,
                DocumentConsumer consumer) {
            ...
            load(loader, prefix + fileExtension, profile, profileFilter, consumer);
        }

        private void load(
                PropertySourceLoader loader,
                String location,
                Profile profile,
                DocumentFilter filter,
                DocumentConsumer consumer) {
            ...
            List<Document> documents = loadDocuments(loader, name, resource);
            ...
        }

        private List<Document> loadDocuments(
                PropertySourceLoader loader,
                String name,
                Resource resource) throws IOException {
            DocumentsCacheKey cacheKey = new DocumentsCacheKey(loader, resource);
            List<Document> documents = this.loadDocumentsCache.get(cacheKey);
            if (documents == null) {
                List<PropertySource<?>> loaded = loader.load(name, resource);
                documents = asDocuments(loaded);
                this.loadDocumentsCache.put(cacheKey, documents);
            }
            return documents;
        }
    }
    ...
}

PropertySourceLoader#getFileExtensions和PropertySourceLoader#load都是接口方法，我们主要看它的YamlPropertySourceLoader实现类的实现

public class YamlPropertySourceLoader implements PropertySourceLoader {
    @Override
    public String[] getFileExtensions() {
        return new String[] { "yml", "yaml" };
    }

    @Override
    public List<PropertySource<?>> load(
            String name,
            Resource resource) throws IOException {
        ...
        return propertySources;
    }
}

最后

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