Spring Boot Application

spring boot默認已經配置了不少環境變量，例如，tomcat的默認端口是8080，項目的contextpath是「/」等等，spring boot容許你自定義一個application.properties文件，而後放在如下的地方，來重寫spring boot的環境變量

spring對配置application.properties的加載過程：

1. 服務啓動調用:SpringApplication.run
2. 建立默認的環境參數：ConfigurableEnvironment
3. 觸發事件：ApplicationEnvironmentPreparedEvent
4. 完成加載

整個過程主要使用spring boot 內置的ConfigFileApplicationListener監聽器監聽ApplicationEnvironmentPreparedEvent事件完成對application.properties加載以及設置。

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下面咱們來跟蹤源碼，看下spring boot是怎樣完成對application.properties文件的加載

• SpringApplication 入口 run：

1.  
   public ConfigurableApplicationContext run(String... args) {
2.  
   //無關的代碼暫略
3.  
   .......
4.  
   ConfigurableApplicationContext context =  null;
5.  
   FailureAnalyzers analyzers =  null;
6.  
   configureHeadlessProperty();
7.  
   //獲取執行監聽器實例
8.  
   SpringApplicationRunListeners listeners = getRunListeners(args);
9.  
   ........
10.  
    //建立全局系統參數實例
11.  
    ApplicationArguments applicationArguments =  new DefaultApplicationArguments(
12.  
    args);
13.  
    //建立 ConfigurableEnvironment 並觸發ApplicationEnvironmentPreparedEvent事件
14.  
    //加載配置的核心地方，spring啓動首要作的事情
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.  
   //建立一個配置環境信息，當是web環境時建立StandardServletEnvironment實例，非web環境時建立StandardEnvironment實例
6.  
   ConfigurableEnvironment environment = getOrCreateEnvironment();
7.  
   configureEnvironment(environment, applicationArguments.getSourceArgs());
8.  
   //核心事件觸發方法，此方法執行後會執行全部監聽ApplicationEnvironmentPreparedEvent事件的監聽器，這裏咱們是跟蹤application.properties文件的加載，就查看ConfigFileApplicationListener監聽器都作了什麼工做
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.  
   //今後處能夠看到當事件爲ApplicationEnvironmentPreparedEvent時，執行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.  
   //此處經過SpringFactoriesLoader加載EnvironmentPostProcessor全部擴展
4.  
   List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
5.  
   //由於此監聽器一樣是EnvironmentPostProcessor的擴展實例，因此在此處將本身加入集合
6.  
   postProcessors. add(this);
7.  
   AnnotationAwareOrderComparator.sort(postProcessors);
8.  
   //遍歷全部的EnvironmentPostProcessor擴展調用postProcessEnvironment
9.  
   //固然咱們跟蹤是application.properties因此主要查看當前實例的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.  
   //此處添加配置信息到environment實例中，此方法完成後就將application.properties加載到環境信息中
5.  
   addPropertySources(environment, application.getResourceLoader());
6.  
   configureIgnoreBeanInfo(environment);
7.  
   bindToSpringApplication(environment, application);
8.  
   }

addPropertySources

1.  
   protected void addPropertySources(ConfigurableEnvironment environment,
2.  
   ResourceLoader resourceLoader) {
3.  
   //這裏先添加一個Random名稱的資源到環境信息中
4.  
   RandomValuePropertySource.addToEnvironment(environment);
5.  
   //經過Loader加載application.properties並將信息存入環境信息中
6.  
   new Loader(environment, resourceLoader).load();
7.  
   }

load

1.  
   public void load() {
2.  
   //建立一個資源加載器，spring boot默認支持PropertiesPropertySourceLoader，YamlPropertySourceLoader兩種配置文件的加載
3.  
   this.propertiesLoader = new PropertySourcesLoader();
4.  
   this.activatedProfiles = false;
5.  
   //加載配置profile信息，默認爲default
6.  
   ..........此處省略
7.  
   while (!this.profiles.isEmpty()) {
8.  
   Profile profile =  this.profiles.poll();
9.  
   //遍歷全部查詢路徑，默認路徑有：classpath:/,classpath:/config/,file:./,file:./config/
10.  
    for (String location : getSearchLocations()) {
11.  
    //這裏不單單是加載application.properties，當搜索路徑不是以/結束，默認認爲是文件名已存在的路徑
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.  
    //遍歷要加載的文件名集合，默認爲application
19.  
    for (String name : getSearchNames()) {
20.  
    load(location, name, profile);
21.  
    }
22.  
    }
23.  
    }
24.  
    this.processedProfiles.add(profile);
25.  
    }
26.  
     
27.  
    //將加載完成的配置信息所有保存到環境信息中共享
28.  
    addConfigurationProperties( this.propertiesLoader.getPropertySources());
29.  
    }

load

1.  
   private void load(String location, String name, Profile profile) {
2.  
   //此處根據profile組裝加載的文件名稱以及資源所放置的組信息
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.  
   //資源加載核心方法，此處有兩個實現，當後綴爲，xml或者properties調用PropertiesPropertySourceLoader
9.  
   //當後綴爲yml或者yaml時，調用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.  
   //此處調用PropertiesLoaderUtils工具類加載本地文件
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就真正的加載並共享到環境信息中，供系統其它地方調用