Spring Boot Application

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：

1.  
   public ConfigurableApplicationContext run(String... args) {
2.  
   //无关的代码暂略
3.  
   .......
4.  
   ConfigurableApplicationContext context = null;
5.  
   FailureAnalyzers analyzers = null;
6.  
   configureHeadlessProperty();
7.  
   //获取执行监听器实例
8.  
   SpringApplicationRunListeners listeners = getRunListeners(args);
9.  
   ........
10.  
    //创建全局系统参数实例
11.  
    ApplicationArguments applicationArguments = new DefaultApplicationArguments(
12.  
    args);
13.  
    //创建 ConfigurableEnvironment 并触发ApplicationEnvironmentPreparedEvent事件
14.  
    //加载配置的核心地方，spring启动首要做的事情
15.  
    ConfigurableEnvironment environment = prepareEnvironment(listeners,
16.  
    applicationArguments);
17.  
    .........
18.  
    }

prepareEnvironment方法

1.  
   private ConfigurableEnvironment prepareEnvironment(
2.  
   SpringApplicationRunListeners listeners,
3.  
   ApplicationArguments applicationArguments) {
4.  
   // Create and configure the environment
5.  
   //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
6.  
   ConfigurableEnvironment environment = getOrCreateEnvironment();
7.  
   configureEnvironment(environment, applicationArguments.getSourceArgs());
8.  
   //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
9.  
   listeners.environmentPrepared(environment);
10.  
    if (!this.webEnvironment) {
11.  
    environment = new EnvironmentConverter(getClassLoader())
12.  
    .convertToStandardEnvironmentIfNecessary(environment);
13.  
    }
14.  
    return environment;
15.  
    }

• ConfigFileApplicationListener：

1.  
   public void onApplicationEvent(ApplicationEvent event) {
2.  
   //从此处可以看到当事件为ApplicationEnvironmentPreparedEvent时，执行onApplicationEnvironmentPreparedEvent方法
3.  
   if (event instanceof ApplicationEnvironmentPreparedEvent) {
4.  
   onApplicationEnvironmentPreparedEvent(
5.  
   (ApplicationEnvironmentPreparedEvent) event);
6.  
   }
7.  
   if (event instanceof ApplicationPreparedEvent) {
8.  
   onApplicationPreparedEvent(event);
9.  
   }
10.  
    }

onApplicationEnvironmentPreparedEvent

1.  
   private void onApplicationEnvironmentPreparedEvent(
2.  
   ApplicationEnvironmentPreparedEvent event) {
3.  
   //此处通过SpringFactoriesLoader加载EnvironmentPostProcessor所有扩展
4.  
   List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
5.  
   //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
6.  
   postProcessors.add(this);
7.  
   AnnotationAwareOrderComparator.sort(postProcessors);
8.  
   //遍历所有的EnvironmentPostProcessor扩展调用postProcessEnvironment
9.  
   //当然我们跟踪是application.properties所以主要查看当前实例的postProcessEnvironment方法
10.  
    for (EnvironmentPostProcessor postProcessor : postProcessors) {
11.  
    postProcessor.postProcessEnvironment(event.getEnvironment(),
12.  
    event.getSpringApplication());
13.  
    }
14.  
    }

postProcessEnvironment

1.  
   @Override
2.  
   public void postProcessEnvironment(ConfigurableEnvironment environment,
3.  
   SpringApplication application) {
4.  
   //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
5.  
   addPropertySources(environment, application.getResourceLoader());
6.  
   configureIgnoreBeanInfo(environment);
7.  
   bindToSpringApplication(environment, application);
8.  
   }

addPropertySources

1.  
   protected void addPropertySources(ConfigurableEnvironment environment,
2.  
   ResourceLoader resourceLoader) {
3.  
   //这里先添加一个Random名称的资源到环境信息中
4.  
   RandomValuePropertySource.addToEnvironment(environment);
5.  
   //通过Loader加载application.properties并将信息存入环境信息中
6.  
   new Loader(environment, resourceLoader).load();
7.  
   }

load

1.  
   public void load() {
2.  
   //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
3.  
   this.propertiesLoader = new PropertySourcesLoader();
4.  
   this.activatedProfiles = false;
5.  
   //加载配置profile信息，默认为default
6.  
   ..........此处省略
7.  
   while (!this.profiles.isEmpty()) {
8.  
   Profile profile = this.profiles.poll();
9.  
   //遍历所有查询路径，默认路径有：classpath:/,classpath:/config/,file:./,file:./config/
10.  
    for (String location : getSearchLocations()) {
11.  
    //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
12.  
    if (!location.endsWith("/")) {
13.  
    // location is a filename already, so don't search for more
14.  
    // filenames
15.  
    load(location, null, profile);
16.  
    }
17.  
    else {
18.  
    //遍历要加载的文件名集合，默认为application
19.  
    for (String name : getSearchNames()) {
20.  
    load(location, name, profile);
21.  
    }
22.  
    }
23.  
    }
24.  
    this.processedProfiles.add(profile);
25.  
    }
26.  
     
27.  
    //将加载完成的配置信息全部保存到环境信息中共享
28.  
    addConfigurationProperties(this.propertiesLoader.getPropertySources());
29.  
    }

load

1.  
   private void load(String location, String name, Profile profile) {
2.  
   //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
3.  
   String group = "profile=" + (profile == null ? "" : profile);
4.  
   if (!StringUtils.hasText(name)) {
5.  
   // Try to load directly from the location
6.  
   loadIntoGroup(group, location, profile);
7.  
   }
8.  
   else {
9.  
    
10.  
    // Also try the profile-specific section (if any) of the normal file
11.  
    loadIntoGroup(group, location + name + "." + ext, profile);
12.  
    }
13.  
    }
14.  
    }

loadIntoGroup

1.  
   private PropertySource<?> doLoadIntoGroup(String identifier, String location,
2.  
   Profile profile) throws IOException {
3.  
   Resource resource = this.resourceLoader.getResource(location);
4.  
   PropertySource<?> propertySource = null;
5.  
   if (resource != null && resource.exists()) {
6.  
   String name = "applicationConfig: [" + location + "]";
7.  
   String group = "applicationConfig: [" + identifier + "]";
8.  
   //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
9.  
   //当后缀为yml或者yaml时，调用YamlPropertySourceLoader
10.  
     
11.  
    propertySource = this.propertiesLoader.load(resource,
12.  
    }
13.  
     
14.  
    return propertySource;
15.  
    }

• PropertiesPropertySourceLoader：

1.  
   @Override
2.  
   public PropertySource<?> load(String name, Resource resource, String profile)
3.  
   throws IOException {
4.  
   if (profile == null) {
5.  
   //此处调用PropertiesLoaderUtils工具类加载本地文件
6.  
   Properties properties = PropertiesLoaderUtils.loadProperties(resource);
7.  
   if (!properties.isEmpty()) {
8.  
   return new PropertiesPropertySource(name, properties);
9.  
   }
10.  
    }
11.  
    return null;
12.  
    }

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