Springboot中PropertySource的结构与加载过程逐步分析讲解

protected void customizePropertySources(MutablePropertySources propertySources) {
		propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
		propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
		if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
			propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));
		}
		super.customizePropertySources(propertySources);
	}

protected void customizePropertySources(MutablePropertySources propertySources) {
		propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
		propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
	}

 <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/springMVC-servlet.xml</param-value>
 </context-param>
<servlet>
        <servlet-name>springMVC</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
                 <param-name>home-page</param-name>
                 <param-value>home.jsp</param-value>
        </init-param>
  </servlet>

public abstract class PropertySource<T> {
	protected final Log logger = LogFactory.getLog(getClass());
	protected final String name;
	protected final T source;
	public PropertySource(String name, T source) {
		Assert.hasText(name, "Property source name must contain at least one character");
		Assert.notNull(source, "Property source must not be null");
		this.name = name;
		this.source = source;
	}
	@SuppressWarnings("unchecked")
	public PropertySource(String name) {
		this(name, (T) new Object());
	}
	public String getName() {
		return this.name;
	}
	public T getSource() {
		return this.source;
	}
	public boolean containsProperty(String name) {
		return (getProperty(name) != null);
	}
	@Nullable
	public abstract Object getProperty(String name);
	@Override
	public boolean equals(Object other) {
		return (this == other || (other instanceof PropertySource &&
				ObjectUtils.nullSafeEquals(this.name, ((PropertySource<?>) other).name)));
	}
	@Override
	public int hashCode() {
		return ObjectUtils.nullSafeHashCode(this.name);
	}
	@Override
	public String toString() {
		if (logger.isDebugEnabled()) {
			return getClass().getSimpleName() + "@" + System.identityHashCode(this) +
					" {name='" + this.name + "', properties=" + this.source + "}";
		}
		else {
			return getClass().getSimpleName() + " {name='" + this.name + "'}";
		}
	}
	public static PropertySource<?> named(String name) {
		return new ComparisonPropertySource(name);
	}
	//StubPropertySource内部类，存根PropertySouece 目的是为了，延迟加载。
	//即有些propertysource使用了一些占位符号，不能早于application context 加载，此时需要进行存根。
	//等到对应的资源加载之后再加载当前的propertysource。占位符会在容器的refresh阶段被替换，
	//具体解析可以查看AbstractApplicationContext#initPropertySources()
	public static class StubPropertySource extends PropertySource<Object> {
		public StubPropertySource(String name) {
			super(name, new Object());
		}
		
		@Override
		@Nullable
		public String getProperty(String name) {
			return null;
		}
	}
	//静态内部类为了named方法使用，仅仅用户比较，调用其它方法会报异常，这里是个适配器模式。
	static class ComparisonPropertySource extends StubPropertySource {
		private static final String USAGE_ERROR =
				"ComparisonPropertySource instances are for use with collection comparison only";
		public ComparisonPropertySource(String name) {
			super(name);
		}
		@Override
		public Object getSource() {
			throw new UnsupportedOperationException(USAGE_ERROR);
		}
		@Override
		public boolean containsProperty(String name) {
			throw new UnsupportedOperationException(USAGE_ERROR);
		}
		@Override
		@Nullable
		public String getProperty(String name) {
			throw new UnsupportedOperationException(USAGE_ERROR);
		}
	}
}

public void onApplicationEvent(ApplicationEvent event) {
		if (event instanceof ApplicationEnvironmentPreparedEvent) {
			onApplicationEnvironmentPreparedEvent(
					(ApplicationEnvironmentPreparedEvent) event);
		}
		if (event instanceof ApplicationPreparedEvent) {
			onApplicationPreparedEvent(event);
		}
	}

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

public void load() {
			this.profiles = new LinkedList<>();
			this.processedProfiles = new LinkedList<>();
			this.activatedProfiles = false;
			this.loaded = new LinkedHashMap<>();
			//初始化默认的profile=default
			initializeProfiles();
			while (!this.profiles.isEmpty()) {
				Profile profile = this.profiles.poll();
				if (profile != null && !profile.isDefaultProfile()) {
					addProfileToEnvironment(profile.getName());
				}
				load(profile, this::getPositiveProfileFilter,
						addToLoaded(MutablePropertySources::addLast, false));
				this.processedProfiles.add(profile);
			}
			resetEnvironmentProfiles(this.processedProfiles);
			load(null, this::getNegativeProfileFilter,
					addToLoaded(MutablePropertySources::addFirst, true));
			addLoadedPropertySources();
		}

private void reorderSources(ConfigurableEnvironment environment) {
			PropertySource<?> defaultProperties = environment.getPropertySources()
					.remove(DEFAULT_PROPERTIES);
			if (defaultProperties != null) {
				environment.getPropertySources().addLast(defaultProperties);
			}
		}