Spring-Boot--application-propert

spring boot默认已经配置了很多环境变量，例如，tomcat的默认端口是8080，项目的contextpath是“/”等等，spring boot允许你自定义一个application.properties文件，然后放在以下的地方，来重写spring boot的环境变量

spring对配置application.properties的加载过程：

1. 服务启动调用:SpringApplication.run
2. 创建默认的环境参数：ConfigurableEnvironment
3. 触发事件：ApplicationEnvironmentPreparedEvent
4. 完成加载

整个过程主要使用spring boot 内置的ConfigFileApplicationListener监听器监听ApplicationEnvironmentPreparedEvent事件完成对application.properties加载以及设置。

---

下面我们来跟踪源码，看下spring boot是怎样完成对application.properties文件的加载

• SpringApplication 入口 run：

public ConfigurableApplicationContext run(String... args) {
        //无关的代码暂略
        .......
        ConfigurableApplicationContext context = null;
        FailureAnalyzers analyzers = null;
        configureHeadlessProperty();
        //获取执行监听器实例
        SpringApplicationRunListeners listeners = getRunListeners(args);
        ........
            //创建全局系统参数实例
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            //创建    ConfigurableEnvironment 并触发ApplicationEnvironmentPreparedEvent事件    
            //加载配置的核心地方，spring启动首要做的事情
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
      .........
    }

prepareEnvironment方法

private ConfigurableEnvironment prepareEnvironment(
            SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments) {
        // Create and configure the environment
        //创建一个配置环境信息，当是web环境时创建StandardServletEnvironment实例，非web环境时创建StandardEnvironment实例
        ConfigurableEnvironment environment = getOrCreateEnvironment();
        configureEnvironment(environment, applicationArguments.getSourceArgs());
        //核心事件触发方法，此方法执行后会执行所有监听ApplicationEnvironmentPreparedEvent事件的监听器，这里我们是跟踪application.properties文件的加载，就查看ConfigFileApplicationListener监听器都做了什么工作
        listeners.environmentPrepared(environment);
        if (!this.webEnvironment) {
            environment = new EnvironmentConverter(getClassLoader())
                    .convertToStandardEnvironmentIfNecessary(environment);
        }
        return environment;
    }

• ConfigFileApplicationListener：

public void onApplicationEvent(ApplicationEvent event) {
        //从此处可以看到当事件为ApplicationEnvironmentPreparedEvent时，执行onApplicationEnvironmentPreparedEvent方法
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            onApplicationEnvironmentPreparedEvent(
                    (ApplicationEnvironmentPreparedEvent) event);
        }
        if (event instanceof ApplicationPreparedEvent) {
            onApplicationPreparedEvent(event);
        }
    }

onApplicationEnvironmentPreparedEvent

private void onApplicationEnvironmentPreparedEvent(
            ApplicationEnvironmentPreparedEvent event) {
        //此处通过SpringFactoriesLoader加载EnvironmentPostProcessor所有扩展   
        List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
        //因为此监听器同样是EnvironmentPostProcessor的扩展实例，所以在此处将自己加入集合
        postProcessors.add(this);
        AnnotationAwareOrderComparator.sort(postProcessors);
        //遍历所有的EnvironmentPostProcessor扩展调用postProcessEnvironment
        //当然我们跟踪是application.properties所以主要查看当前实例的postProcessEnvironment方法
        for (EnvironmentPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessEnvironment(event.getEnvironment(),
                    event.getSpringApplication());
        }
    }

postProcessEnvironment

@Override
    public void postProcessEnvironment(ConfigurableEnvironment environment,
            SpringApplication application) {
        //此处添加配置信息到environment实例中，此方法完成后就将application.properties加载到环境信息中
        addPropertySources(environment, application.getResourceLoader());
        configureIgnoreBeanInfo(environment);
        bindToSpringApplication(environment, application);
    }

addPropertySources

protected void addPropertySources(ConfigurableEnvironment environment,
            ResourceLoader resourceLoader) {
        //这里先添加一个Random名称的资源到环境信息中  
        RandomValuePropertySource.addToEnvironment(environment);
        //通过Loader加载application.properties并将信息存入环境信息中
        new Loader(environment, resourceLoader).load();
    }

load

public void load() {
//创建一个资源加载器，spring boot默认支持PropertiesPropertySourceLoader，YamlPropertySourceLoader两种配置文件的加载
            this.propertiesLoader = new PropertySourcesLoader();
            this.activatedProfiles = false;
            //加载配置profile信息，默认为default
            ..........此处省略
            while (!this.profiles.isEmpty()) {
                Profile profile = this.profiles.poll();
                //遍历所有查询路径，默认路径有：classpath:/,classpath:/config/,file:./,file:./config/
                for (String location : getSearchLocations()) {
                //这里不仅仅是加载application.properties，当搜索路径不是以/结束，默认认为是文件名已存在的路径
                    if (!location.endsWith("/")) {
                        // location is a filename already, so don't search for more
                        // filenames
                        load(location, null, profile);
                    }
                    else {
                         //遍历要加载的文件名集合，默认为application
                        for (String name : getSearchNames()) {
                            load(location, name, profile);
                        }
                    }
                }
                this.processedProfiles.add(profile);
            }

            //将加载完成的配置信息全部保存到环境信息中共享
            addConfigurationProperties(this.propertiesLoader.getPropertySources());
        }

load

private void load(String location, String name, Profile profile) {
            //此处根据profile组装加载的文件名称以及资源所放置的组信息
            String group = "profile=" + (profile == null ? "" : profile);
            if (!StringUtils.hasText(name)) {
                // Try to load directly from the location
                loadIntoGroup(group, location, profile);
            }
            else {
             
                    // Also try the profile-specific section (if any) of the normal file
                    loadIntoGroup(group, location + name + "." + ext, profile);
                }
            }
        }

loadIntoGroup

private PropertySource<?> doLoadIntoGroup(String identifier, String location,
                Profile profile) throws IOException {
            Resource resource = this.resourceLoader.getResource(location);
            PropertySource<?> propertySource = null;
            if (resource != null && resource.exists()) {
                String name = "applicationConfig: [" + location + "]";
                String group = "applicationConfig: [" + identifier + "]";
                //资源加载核心方法，此处有两个实现，当后缀为，xml或者properties调用PropertiesPropertySourceLoader
                //当后缀为yml或者yaml时，调用YamlPropertySourceLoader
                
                propertySource = this.propertiesLoader.load(resource, 
            }
        
            return propertySource;
        }

• PropertiesPropertySourceLoader：

@Override
    public PropertySource<?> load(String name, Resource resource, String profile)
            throws IOException {
        if (profile == null) {
            //此处调用PropertiesLoaderUtils工具类加载本地文件
            Properties properties = PropertiesLoaderUtils.loadProperties(resource);
            if (!properties.isEmpty()) {
                return new PropertiesPropertySource(name, properties);
            }
        }
        return null;
    }

到此application.properties就真正的加载并共享到环境信息中，供系统其它地方调用。