通过源码了解springboot加载application.properties过程

通过源码了解springboot加载application.properties过程
原创天才小汪汪发布于2018-09-27 16:52:31 阅读数 2494 收藏
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springboot有一个配置文件application.properties,我只知道有这么一个配置文件,但是springboot启动的时候,是在哪里加载该文件的,又如何找到该文件的?从源码去查看

在main方法里执行该方法SpringApplication.run(Test.class, args);查看SpringApplication类的源码,进入run方法

public static ConfigurableApplicationContext run(Object source, String... args) {
return run(new Object[] { source }, args);
}

再进入 run(new Object[] { source }, args);方法

public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
return new SpringApplication(sources).run(args);
}

到这一步,可以看到创建一个新的SpringApplication,new SpringApplication(sources),并执行run()方法,先到构造方法去看一下,这类做了什么初始化的事

public SpringApplication(Object... sources) {
initialize(sources);
}

里面有一个initialize(sources);方法,再进去

@SuppressWarnings({ "unchecked", "rawtypes" })
   private void initialize(Object[] sources) {
       if (sources != null && sources.length > 0) {
           this.sources.addAll(Arrays.asList(sources));
       }
       this.webEnvironment = deduceWebEnvironment();
       setInitializers((Collection) getSpringFactoriesInstances(
               ApplicationContextInitializer.class));
       setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
       this.mainApplicationClass = deduceMainApplicationClass();
   }

在上面的代码中, this.webEnvironment = deduceWebEnvironment();该方法主要是筛选sevlet和ConfigurableWebApplicationContext,如何有这两个就返回false,否则返回true,具体有什么作用,我也不知道,但跟这次讨论的问题无关,暂时放一边,setInitalizers()方法,看一下源码

public void setInitializers(
           Collection<? extends ApplicationContextInitializer<?>> initializers) {
       this.initializers = new ArrayList<ApplicationContextInitializer<?>>();
       this.initializers.addAll(initializers);
   }

该方法就是将ApplicationContextInitializer的实现类加入 this.initializers集合中,在getSpringFactoriesInstances(
ApplicationContextInitializer.class)方法中,利用反射获取实现类的集合

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
           Class<?>[] parameterTypes, Object... args) {
       ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
       // Use names and ensure unique to protect against duplicates
       Set<String> names = new LinkedHashSet<String>(
               SpringFactoriesLoader.loadFactoryNames(type, classLoader));
       List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
               classLoader, args, names);
       AnnotationAwareOrderComparator.sort(instances);
       return instances;
   }

在this.initializers中存放的就springboot所要加载的ApplicationContextInitializer实现类

[org.springframework.boot.context.config.DelegatingApplicationContextInitializer,

org.springframework.boot.context.ContextIdApplicationContextInitializer,

org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,

org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer,

org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,

org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer]

在这些实现类中,也没有涉及到application.properties文件的加载,暂时也不管,来看 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));方法,和上面加载ApplicationContextInitializer步骤一样,在this.listeners存储的ApplicationListener便有以下这些

[org.springframework.boot.context.config.ConfigFileApplicationListener,

org.springframework.boot.context.config.AnsiOutputApplicationListener,

org.springframework.boot.logging.LoggingApplicationListener,

org.springframework.boot.logging.ClasspathLoggingApplicationListener,

org.springframework.boot.autoconfigure.BackgroundPreinitializer,

org.springframework.boot.context.config.DelegatingApplicationListener,

org.springframework.boot.builder.ParentContextCloserApplicationListener,

org.springframework.boot.ClearCachesApplicationListener

org.springframework.boot.context.FileEncodingApplicationListener,

org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener]

到这里便可以看到一个很重要的监听器ConfigFileApplicationListener

public class ConfigFileApplicationListener implements EnvironmentPostProcessor,
ApplicationListener<ApplicationEvent>, Ordered {

private static final String DEFAULT_PROPERTIES = "defaultProperties";

// Note the order is from least to most specific (last one wins)
private static final String DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/"; //默认加载的位置

private static final String DEFAULT_NAMES = "application"; //默认的配置文件名

   /**
   * The "active profiles" property name.
   */
   public static final String ACTIVE_PROFILES_PROPERTY = "spring.profiles.active";

   /**
   * The "includes profiles" property name.
   */
   public static final String INCLUDE_PROFILES_PROPERTY = "spring.profiles.include";

   /**
   * The "config name" property name.
   */
   public static final String CONFIG_NAME_PROPERTY = "spring.config.name";

   /**
   * The "config location" property name.
   */
   public static final String CONFIG_LOCATION_PROPERTY = "spring.config.location";

   /**
   * The default order for the processor.
   */
   public static final int DEFAULT_ORDER = Ordered.HIGHEST_PRECEDENCE + 10;

   /**
   * Name of the application configuration {@link PropertySource}.
   */
   public static final String APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME = "applicationConfigurationProperties";

private final DeferredLog logger = new DeferredLog();

private String searchLocations;

private String names;

private int order = DEFAULT_ORDER;

private final ConversionService conversionService = new DefaultConversionService();

   @Override
   public void onApplicationEvent(ApplicationEvent event) {
.............................
   }
................

}

到这里终于找到了加载application.properties的类了,该类便是解析application.properties里配置的各个属性值,在prependProfile()方法解析.

以上,SpringApplication只是将该类存在一个集合中,那么它又是在哪里开启这些监听呢

到这里,进入run()方法去看一下

public ConfigurableApplicationContext run(String... args) {
//...........
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();

//...................

}

在这里,得到的是一个SpringApplicationRunListeners的实现类EventPublishingRunListener,并将其开启监听,EventPublishingRunListener里面如下做了如下处理

public EventPublishingRunListener(SpringApplication application, String[] args) {
       this.application = application;
       this.args = args;
       this.initialMulticaster = new SimpleApplicationEventMulticaster();
       for (ApplicationListener<?> listener : application.getListeners()) {
           this.initialMulticaster.addApplicationListener(listener);
       }
   }

在EventPublishingRunListener的构造函数里,application.getListeners()获取的就是SpringApplication中的this.listeners集合里存放的Listener.再来看listeners.starting();方法做了什么

public void starting() {
       for (SpringApplicationRunListener listener : this.listeners) {
           listener.starting();
       }
   }

它把集合里的所有listener都开启了监听.到此加载application.properties结束.

总结:

springboot通过SpringApplication类的构造函数,加载所需要的listener,在run()方法执行里,由EventPublishingRunListener开启所有的listener的监听.
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版权声明：本文为CSDN博主「天才小汪汪」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/qq_36009027/article/details/82868431

通过源码了解springboot加载application.properties过程

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