public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    private long startupDate;
    /** Flag that indicates whether this context is currently active. */
    private final AtomicBoolean active = new AtomicBoolean();
    /** Flag that indicates whether this context has been closed already. */
    private final AtomicBoolean closed = new AtomicBoolean();
    /** Environment used by this context. */
    @Nullable
    private ConfigurableEnvironment environment;
    protected void prepareRefresh() {
        // Switch to active.
        this.startupDate = System.currentTimeMillis();
        // 1. 初始化狀態(tài)位
        this.closed.set(false);
        this.active.set(true);
        if (logger.isDebugEnabled()) {
            if (logger.isTraceEnabled()) {
                logger.trace("Refreshing " + this);
            } else {
                logger.debug("Refreshing " + getDisplayName());
            }
        }
        // 2. 留給子類的擴展方法
        // Initialize any placeholder property sources in the context environment.
        initPropertySources();
        // 3. 驗證必須的配置項是否存在
        // Validate that all properties marked as required are resolvable:
        // see ConfigurablePropertyResolver#setRequiredProperties
        getEnvironment().validateRequiredProperties();
        // 4. 處理早期事件
        // Store pre-refresh ApplicationListeners...
        if (this.earlyApplicationListeners == null) {
            this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
        } else {
            // Reset local application listeners to pre-refresh state.
            this.applicationListeners.clear();
            this.applicationListeners.addAll(this.earlyApplicationListeners);
        }
        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }
}

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    protected void doClose() {
        // 當前是激活狀態(tài) && 還沒有被關閉
        // Check whether an actual close attempt is necessary...
        if (this.active.get() && this.closed.compareAndSet(false, true)) {
            // 這里省略 N 行代碼
            // 這里省略 N 行代碼
            // Switch to inactive.
            this.active.set(false);
        }
    }
}

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    protected void assertBeanFactoryActive() {
        if (!this.active.get()) {
            if (this.closed.get()) {
                throw new IllegalStateException(getDisplayName() + " has been closed already");
            } else {
                throw new IllegalStateException(getDisplayName() + " has not been refreshed yet");
            }
        }
    }
}

public abstract class AbstractRefreshableWebApplicationContext extends AbstractRefreshableConfigApplicationContext
        implements ConfigurableWebApplicationContext, ThemeSource {
    @Override
    protected void initPropertySources() {
        ConfigurableEnvironment env = getEnvironment();
        if (env instanceof ConfigurableWebEnvironment) {
            // 這里實際上是調用了 WebApplicationContextUtils#initServletPropertySources
            ((ConfigurableWebEnvironment) env).initPropertySources(this.servletContext, this.servletConfig);
        }
    }
}
public abstract class WebApplicationContextUtils {
    public static void initServletPropertySources(MutablePropertySources sources,
                                                  @Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) {
        Assert.notNull(sources, "'propertySources' must not be null");
        String name = StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME;
        // servletContextInitParams
        if (servletContext != null && sources.get(name) instanceof StubPropertySource) {
            sources.replace(name, new ServletContextPropertySource(name, servletContext));
        }
        name = StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME;
        // servletConfigInitParams
        if (servletConfig != null && sources.get(name) instanceof StubPropertySource) {
            sources.replace(name, new ServletConfigPropertySource(name, servletConfig));
        }
    }
}

public class PrepareRefreshTest {
    /**
     * 重寫 initPropertySources()，給 Environment 中新增兩個自定義的配置項 "osName" 和 "a.b.c.d"
     */
    @Test
    void initPropertySourcesTest() {
        final ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PrepareRefreshTest.class) {
            @Override
            protected void initPropertySources() {
                super.initPropertySources();
                final ConfigurableEnvironment environment = getEnvironment();
                final Map<String, Object> config = new HashMap<>();
                config.put("osName", System.getProperty("os.name", "UNKNOWN"));
                config.put("a.b.c.d", "haha");
                environment.getPropertySources().addFirst(new MapPropertySource("demo-property-source", config));
            }
        };
        final Environment environment = applicationContext.getEnvironment();
        Assertions.assertEquals(System.getProperty("os.name"), environment.getProperty("osName"));
        Assertions.assertEquals("haha", environment.getProperty("a.b.c.d"));
    }
}

public abstract class AbstractPropertyResolver implements ConfigurablePropertyResolver {
    @Override
    public void validateRequiredProperties() {
        MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException();
        for (String key : this.requiredProperties) {
            if (this.getProperty(key) == null) {
                ex.addMissingRequiredProperty(key);
            }
        }
        if (!ex.getMissingRequiredProperties().isEmpty()) {
            throw ex;
        }
    }
}

public class PrepareRefreshTest {
    /**
     * 驗證 getEnvironment().validateRequiredProperties(); 的功能
     * <p>
     * 拋出 MissingRequiredPropertiesException 異常(Environment 中缺少必須出現的配置項"jdbc.url")
     */
    @Test
    void validateRequiredPropertiesTest() {
        Assertions.assertThrows(MissingRequiredPropertiesException.class, () -> {
                    final ApplicationContext applicationContext = new AnnotationConfigApplicationContext(PrepareRefreshTest.class) {
                        @Override
                        protected void initPropertySources() {
                            super.initPropertySources();
                            // 這里指定 Environment 中必須要有一個名為 "jdbc.url" 的配置項
                            // 如果 Environment 中沒有名為 "jdbc.url" 的配置項, 就會在 validateRequiredProperties() 方法中拋出 MissingRequiredPropertiesException
                            getEnvironment().setRequiredProperties("jdbc.url");
                        }
                    };
                }
        );
    }
}

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext {
    private final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet<>();
    /** Local listeners registered before refresh. */
    @Nullable
    private Set<ApplicationListener<?>> earlyApplicationListeners;
    /** ApplicationEvents published before the multicaster setup. */
    @Nullable
    private Set<ApplicationEvent> earlyApplicationEvents;
    protected void prepareRefresh() {
        // Switch to active.
        // 1. 初始化狀態(tài)位
        // ...
        // 2. 留給子類的擴展方法
        // ...
        // 3. 驗證必須的配置項是否存在
        // ...
        // 4. 處理早期事件
        // Store pre-refresh ApplicationListeners...
        if (this.earlyApplicationListeners == null) {
            this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
        } else {
            // Reset local application listeners to pre-refresh state.
            this.applicationListeners.clear();
            this.applicationListeners.addAll(this.earlyApplicationListeners);
        }
        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }
}