ApplicationContext

ApplicationContext是个接口，实际上也是一个BeanFactory，不过比BeanFactory更加强大。

ApplicationContext源码

public interface ApplicationContext extends EnvironmentCapable, ListableBeanFactory, HierarchicalBeanFactory,MessageSource, ApplicationEventPublisher, ResourcePatternResolver {/*** Return the unique id of this application context.* @return the unique id of the context, or {@code null} if none*/@NullableString getId();/*** Return a name for the deployed application that this context belongs to.* @return a name for the deployed application, or the empty String by default*/String getApplicationName();/*** Return a friendly name for this context.* @return a display name for this context (never {@code null})*/String getDisplayName();/*** Return the timestamp when this context was first loaded.* @return the timestamp (ms) when this context was first loaded*/long getStartupDate();/*** Return the parent context, or {@code null} if there is no parent* and this is the root of the context hierarchy.* @return the parent context, or {@code null} if there is no parent*/@NullableApplicationContext getParent();/*** Expose AutowireCapableBeanFactory functionality for this context.* <p>This is not typically used by application code, except for the purpose of* initializing bean instances that live outside of the application context,* applying the Spring bean lifecycle (fully or partly) to them.* <p>Alternatively, the internal BeanFactory exposed by the* {@link ConfigurableApplicationContext} interface offers access to the* {@link AutowireCapableBeanFactory} interface too. The present method mainly* serves as a convenient, specific facility on the ApplicationContext interface.* <p><b>NOTE: As of 4.2, this method will consistently throw IllegalStateException* after the application context has been closed.</b> In current Spring Framework* versions, only refreshable application contexts behave that way; as of 4.2,* all application context implementations will be required to comply.* @return the AutowireCapableBeanFactory for this context* @throws IllegalStateException if the context does not support the* {@link AutowireCapableBeanFactory} interface, or does not hold an* autowire-capable bean factory yet (e.g. if {@code refresh()} has* never been called), or if the context has been closed already* @see ConfigurableApplicationContext#refresh()* @see ConfigurableApplicationContext#getBeanFactory()*/AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException;}

ApplicationContext继承接口分析

1. HierarchicalBeanFactory：拥有获取父BeanFactory的功能

2. ListableBeanFactory：拥有获取beanNames的功能

3. ResourcePatternResolver：资源加载器，可以一次性获取多个资源（文件资源等等）

4. EnvironmentCapable：可以获取运行时环境（没有设置运行时环境功能）

5. ApplicationEventPublisher：拥有广播事件的功能（没有添加事件监听器的功能）

6. MessageSource：拥有国际化功能

ApplicationContext两个比较重要的实现类

AnnotationConfigApplicationContext

类继承实现结构：

类图说明：

1. ConfigurableApplicationContext：继承了ApplicationContext接口，增加了，添加事件监听器、添加BeanFactoryPostProcessor、设置Environment，获取ConfigurableListableBeanFactory等功能

2. AbstractApplicationContext：实现了ConfigurableApplicationContext接口

3. GenericApplicationContext：继承了AbstractApplicationContext，实现了BeanDefinitionRegistry接口，拥有了所有ApplicationContext的功能，并且可以注册BeanDefinition，注意这个类中有一个属性(DefaultListableBeanFactory beanFactory)

4. AnnotationConfigRegistry：可以单独注册某个为类为BeanDefinition（可以处理该类上的**@Configuration注解**，已经可以处理**@Bean注解**），同时可以扫描

5. AnnotationConfigApplicationContext：继承了GenericApplicationContext，实现了AnnotationConfigRegistry接口，拥有了以上所有的功能

ClassPathXmlApplicationContext

类继承实现结构：

它也是继承了AbstractApplicationContext，但是相对于AnnotationConfigApplicationContext而言，功能没有AnnotationConfigApplicationContext强大，比如不能注册BeanDefinition

国际化—MessageSource

messages.properties：

test=你好
demo=测试指定字符串{0}

messages_en.properties：

test=hello
demo=test str{0}

AppConfig：

    @Beanpublic MessageSource messageSource() {ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();messageSource.setBasename("messages");return messageSource;}

Main：

    public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);//context.refresh();System.out.println(context.getMessage("test", null, Locale.getDefault()));System.out.println(context.getMessage("test", null, Locale.CHINA));System.out.println(context.getMessage("test", null, Locale.US));System.out.println(context.getMessage("demo", new String[]{"1"}, Locale.getDefault()));System.out.println(context.getMessage("demo", new String[]{"1"}, Locale.US));}

资源加载—ResourceLoader

    public static void main(String[] args) throws IOException {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);Resource resource = context.getResource("file://D:\\javaProject\\tuling-code\\spring\\src\\main\\java\\top\\mingempty\\spring\\config\\AppConfig.java");System.out.println(resource.getFilename());System.out.println(resource.contentLength());Resource resource1 = context.getResource("https://www.baidu.com");System.out.println(resource1.contentLength());System.out.println(resource1.getURL());Resource resource2 = context.getResource("classpath:spring.xml");System.out.println(resource2.contentLength());System.out.println(resource2.getURL());//获取多个Resource[] resources = context.getResources("classpath:top/mingempty/spring/*");for (Resource resource3 : resources) {System.out.println(resource3.contentLength());System.out.println(resource3.getFilename());}}

获取运行时环境—Environment

AppConfig ：

@PropertySource("classpath:spring.properties")
public class AppConfig {}

spring.properties：

environment=Environment

    public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);// 操作系统层面的环境变量Map<String, Object> systemEnvironment = context.getEnvironment().getSystemEnvironment();System.out.println(systemEnvironment);System.out.println("=======");// java运行层面，通过-D指定的Map<String, Object> systemProperties = context.getEnvironment().getSystemProperties();System.out.println(systemProperties);System.out.println("=======");// 前面两者之和MutablePropertySources propertySources = context.getEnvironment().getPropertySources();System.out.println(propertySources);System.out.println("=======");// 系统中存在的环境变量System.out.println(context.getEnvironment().getProperty("MVN_HOME"));System.out.println(context.getEnvironment().getProperty("sun.jnu.encoding"));// 获取一个不存在的System.out.println(context.getEnvironment().getProperty("NULL"));// 获取配置文件内的// @PropertySource("classpath:spring.properties")System.out.println(context.getEnvironment().getProperty("environment"));}

事件发布—ApplicationEventPublisher

AppConfig：注册一个监听事件

public class AppConfig {@Beanpublic ApplicationListener applicationListener() {return event -> {if (event instanceof PayloadApplicationEvent) {PayloadApplicationEvent payloadApplicationEvent = (PayloadApplicationEvent) event;System.out.println("接收到了一个事件:" + payloadApplicationEvent.getPayload());}};}
}

Main：发布消息

    public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);context.publishEvent("abc");}