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
	 */
	@Nullable
	String 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
	 */
	@Nullable
	ApplicationContext 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：

    @Bean
    public 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 {
    @Bean
    public 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");
    }