1. SpringBoot读取配置文件源码探究

1.1. 概览

• springboot的源码是再原来的Spring源码上又包了一层，看过spring源码都知道，当我们从入口debug进去的时候，原来的Spring源码都集中在refreshContext方法，SpringBoot的主要运行步骤，基本都包含在这个方法里了，而这个方法就是我们运行Springboot的主函数SpringApplication.run(Application.class, args);经过几步后到达的

    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        FailureAnalyzers analyzers = null;
        configureHeadlessProperty();
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            Banner printedBanner = printBanner(environment);
            context = createApplicationContext();
            analyzers = new FailureAnalyzers(context);
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            listeners.finished(context, null);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            return context;
        }
        catch (Throwable ex) {
            handleRunFailure(context, listeners, analyzers, ex);
            throw new IllegalStateException(ex);
        }
    }

1.2. 配置读取步骤

1.2.1. prepareEnvironment

• 配置读取的步骤主要就在ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);这一步，我们继续深入

    private ConfigurableEnvironment prepareEnvironment(
            SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments) {
        // Create and configure the environment
        ConfigurableEnvironment environment = getOrCreateEnvironment();
        configureEnvironment(environment, applicationArguments.getSourceArgs());
        //主要是这步
        listeners.environmentPrepared(environment);
        if (!this.webEnvironment) {
            environment = new EnvironmentConverter(getClassLoader())
                    .convertToStandardEnvironmentIfNecessary(environment);
        }
        return environment;
    }

• 创建基本的环境容器后，进入listeners.environmentPrepared(environment);通过监听器来进行环境变量的初始化，同时读取配置也是一部分工作

1.2.2. environmentPrepared

• 下一步，看到对监听器进行循环处理，这里的listeners中，默认只有一个EventPublishRunListener

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

• 继续如下，这一步它进行广播事件了

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

1.2.3. multicastEvent

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

继续，重点是invokeListener方法，去调用监听器事件，可以想象对配置文件来讲，这就是读取配置事件了。同时监听器有很多，读取配置文件的监听器是ConfigFileAplicationListener，看名字还是蛮明显的吧

    @Override
    public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            Executor executor = getTaskExecutor();
            if (executor != null) {
                executor.execute(new Runnable() {
                    @Override
                    public void run() {
                        invokeListener(listener, event);
                    }
                });
            }
            else {
                //重点
                invokeListener(listener, event);
            }
        }
    }

继续，和上一步类似，do真正的事件了

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

    private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
        try {
            // 入口
            listener.onApplicationEvent(event);
        }
        catch (ClassCastException ex) {
            String msg = ex.getMessage();
            if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
                // Possibly a lambda-defined listener which we could not resolve the generic event type for
                // -> let's suppress the exception and just log a debug message.
                Log logger = LogFactory.getLog(getClass());
                if (logger.isDebugEnabled()) {
                    logger.debug("Non-matching event type for listener: " + listener, ex);
                }
            }
            else {
                throw ex;
            }
        }
    }

1.2.4. onApplicationEvent

• 在ConfigFileApplicationListener类中继续

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            //配置入口
            onApplicationEnvironmentPreparedEvent(
                    (ApplicationEnvironmentPreparedEvent) event);
        }
        if (event instanceof ApplicationPreparedEvent) {
            onApplicationPreparedEvent(event);
        }
    }

继续，可以看到处理器有这些，我们关注ConfigFileApplicationListener

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

1.2.5. postProcessEnvironment

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment,
            SpringApplication application) {
        //重点入口
        addPropertySources(environment, application.getResourceLoader());
        configureIgnoreBeanInfo(environment);
        bindToSpringApplication(environment, application);
    }

继续

    protected void addPropertySources(ConfigurableEnvironment environment,
            ResourceLoader resourceLoader) {
        RandomValuePropertySource.addToEnvironment(environment);
        //总算看到加载入口了
        new Loader(environment, resourceLoader).load();
    }

1.2.6. load

public void load() {
            this.propertiesLoader = new PropertySourcesLoader();
            this.activatedProfiles = false;
            this.profiles = Collections.asLifoQueue(new LinkedList<Profile>());
            this.processedProfiles = new LinkedList<Profile>();

            // Pre-existing active profiles set via Environment.setActiveProfiles()
            // are additional profiles and config files are allowed to add more if
            // they want to, so don't call addActiveProfiles() here.
            Set<Profile> initialActiveProfiles = initializeActiveProfiles();
            this.profiles.addAll(getUnprocessedActiveProfiles(initialActiveProfiles));
            if (this.profiles.isEmpty()) {
                for (String defaultProfileName : this.environment.getDefaultProfiles()) {
                    Profile defaultProfile = new Profile(defaultProfileName, true);
                    if (!this.profiles.contains(defaultProfile)) {
                        this.profiles.add(defaultProfile);
                    }
                }
            }

            // The default profile for these purposes is represented as null. We add it
            // last so that it is first out of the queue (active profiles will then
            // override any settings in the defaults when the list is reversed later).
            this.profiles.add(null);

            while (!this.profiles.isEmpty()) {
                Profile profile = this.profiles.poll();
                for (String location : getSearchLocations()) {
                    if (!location.endsWith("/")) {
                        // location is a filename already, so don't search for more
                        // filenames
                        load(location, null, profile);
                    }
                    else {
                        for (String name : getSearchNames()) {
                            //加载入口
                            load(location, name, profile);
                        }
                    }
                }
                this.processedProfiles.add(profile);
            }

            addConfigurationProperties(this.propertiesLoader.getPropertySources());
        }

• 可以看到它的加载名从getSearchNames获取，那就看看这个方法

        private Set<String> getSearchNames() {
            if (this.environment.containsProperty(CONFIG_NAME_PROPERTY)) {
                return asResolvedSet(this.environment.getProperty(CONFIG_NAME_PROPERTY),
                        null);
            }
            return asResolvedSet(ConfigFileApplicationListener.this.names, DEFAULT_NAMES);
        }

• CONFIG_NAME_PROPERTY值为spring.config.name，DEFAULT_NAMES值为application，所以可以看出application这个名字就是默认的配置名了，但也可以用spring.config.name属性来修改

• 其实到这一步，后面已经没难度了，可以想象，接下去应该是拼接出完整的路径，找到文件读取，还是走完流程把

• 继续

        private void load(String location, String name, Profile profile) {
            String group = "profile=" + ((profile != null) ? profile : "");
            if (!StringUtils.hasText(name)) {
                // Try to load directly from the location
                loadIntoGroup(group, location, profile);
            }
            else {
                // Search for a file with the given name
                for (String ext : this.propertiesLoader.getAllFileExtensions()) {
                    if (profile != null) {
                        // Try the profile-specific file
                        loadIntoGroup(group, location + name + "-" + profile + "." + ext,
                                null);
                        for (Profile processedProfile : this.processedProfiles) {
                            if (processedProfile != null) {
                                loadIntoGroup(group, location + name + "-"
                                        + processedProfile + "." + ext, profile);
                            }
                        }
                        // Sometimes people put "spring.profiles: dev" in
                        // application-dev.yml (gh-340). Arguably we should try and error
                        // out on that, but we can be kind and load it anyway.
                        loadIntoGroup(group, location + name + "-" + profile + "." + ext,
                                profile);
                    }
                    // Also try the profile-specific section (if any) of the normal file
                    //加载重点
                    loadIntoGroup(group, location + name + "." + ext, profile);
                }
            }
        }

• 继续

        private PropertySource<?> loadIntoGroup(String identifier, String location,
                Profile profile) {
            try {
                //入口
                return doLoadIntoGroup(identifier, location, profile);
            }
            catch (Exception ex) {
                throw new IllegalStateException(
                        "Failed to load property source from location '" + location + "'",
                        ex);
            }
        }

• do开头都是正式要干事了

        private PropertySource<?> doLoadIntoGroup(String identifier, String location,
                Profile profile) throws IOException {
            Resource resource = this.resourceLoader.getResource(location);
            PropertySource<?> propertySource = null;
            StringBuilder msg = new StringBuilder();
            if (resource != null && resource.exists()) {
                String name = "applicationConfig: [" + location + "]";
                String group = "applicationConfig: [" + identifier + "]";
                // 加载入口
                propertySource = this.propertiesLoader.load(resource, group, name,
                        (profile != null) ? profile.getName() : null);
                if (propertySource != null) {
                    msg.append("Loaded ");
                    handleProfileProperties(propertySource);
                }
                else {
                    msg.append("Skipped (empty) ");
                }
            }
            else {
                msg.append("Skipped ");
            }
            msg.append("config file ");
            msg.append(getResourceDescription(location, resource));
            if (profile != null) {
                msg.append(" for profile ").append(profile);
            }
            if (resource == null || !resource.exists()) {
                msg.append(" resource not found");
                this.logger.trace(msg);
            }
            else {
                this.logger.debug(msg);
            }
            return propertySource;
        }

• load内容，这里有两个加载器，看名字也知道了，yml结尾的文件肯定用YamlPropertySourceLoader才能加载，properties结尾的用另一个
  

    public PropertySource<?> load(Resource resource, String group, String name,
            String profile) throws IOException {
        if (isFile(resource)) {
            String sourceName = generatePropertySourceName(name, profile);
            for (PropertySourceLoader loader : this.loaders) {
                if (canLoadFileExtension(loader, resource)) {
                    // 干事的入口
                    PropertySource<?> specific = loader.load(sourceName, resource,
                            profile);
                    addPropertySource(group, specific);
                    return specific;
                }
            }
        }
        return null;
    }

• 我用的是yml，所以在YamlPropertySourceLoader类

    @Override
    public PropertySource<?> load(String name, Resource resource, String profile)
            throws IOException {
        if (ClassUtils.isPresent("org.yaml.snakeyaml.Yaml", null)) {
            Processor processor = new Processor(resource, profile);
            //真正的处理类
            Map<String, Object> source = processor.process();
            if (!source.isEmpty()) {
                return new MapPropertySource(name, source);
            }
        }
        return null;
    }

        public Map<String, Object> process() {
            final Map<String, Object> result = new LinkedHashMap<String, Object>();
            //接近了
            process(new MatchCallback() {
                @Override
                public void process(Properties properties, Map<String, Object> map) {
                    result.putAll(getFlattenedMap(map));
                }
            });
            return result;
        }

1.2.7. process

    protected void process(MatchCallback callback) {
        Yaml yaml = createYaml();
        for (Resource resource : this.resources) {
            //更近了
            boolean found = process(callback, yaml, resource);
            if (this.resolutionMethod == ResolutionMethod.FIRST_FOUND && found) {
                return;
            }
        }
    }

• 继续深入
  
  
• 可以看到，总算把我配合文件的内容给读到了，然后放入callback

    private boolean process(MatchCallback callback, Yaml yaml, Resource resource) {
        int count = 0;
        try {
            if (logger.isDebugEnabled()) {
                logger.debug("Loading from YAML: " + resource);
            }
            //读取文件
            Reader reader = new UnicodeReader(resource.getInputStream());
            try {
                for (Object object : yaml.loadAll(reader)) {
                    //总算拿到了
                    if (object != null && process(asMap(object), callback)) {
                        count++;
                        if (this.resolutionMethod == ResolutionMethod.FIRST_FOUND) {
                            break;
                        }
                    }
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Loaded " + count + " document" + (count > 1 ? "s" : "") +
                            " from YAML resource: " + resource);
                }
            }
            finally {
                reader.close();
            }
        }
        catch (IOException ex) {
            handleProcessError(resource, ex);
        }
        return (count > 0);
    }

• 结果就存入了result

• 这样之后返回去看，你就会看到它存入了MapPropertySource属性资源，在之后就会被用上了

1.3. 总结

• 我通过一步步的代码跟踪，解析了SpringBoot读取application.yml的整个流程，代码虽然贴的比较多，但可以让初学者也可以跟着这个步骤完整的理解一遍，代码中的关键步骤我都用中文标明了，其它没标注部分不是这章的重点，想研究的自行研究