簡介

spring容器中Bean的生命周期內(nèi)所有可擴展的點的調(diào)用順序

擴展接口	實現(xiàn)接口
ApplicationContextlnitializer	initialize
AbstractApplicationContext	refreshe
BeanDefinitionRegistryPostProcessor	postProcessBeanDefinitionRegistry
BeanDefinitionRegistryPostProcessor	postProcessBeanFactory
BeanFactoryPostProcessor	postProcessBeanFactory
instantiationAwareBeanPostProcessor	postProcessBeforelnstantiation
SmartlnstantiationAwareBeanPostProcessor	determineCandidateConstructors
MergedBeanDefinitionPostProcessor	postProcessMergedBeanDefinition
InstantiationAwareBeanPostProcessor	postProcessAfterlnstantiation
SmartInstantiationAwareBeanPostProcessor	getEarlyBeanReference
BeanNameAware	setBeanName
BeanFactoryAware	postProcessPropertyValues
ApplicationContextAwareProcessor	invokeAwarelnterfaces
InstantiationAwareBeanPostProcessor	postProcessBeforelnstantiation
@PostConstruct
InitializingBean	afterPropertiesSet
FactoryBean	getobject
SmartlnitializingSingleton	afterSingletonslnstantiated
CommandLineRunner	run
DisposableBean	destroy

今天要介紹的是ApplicationContextAwareProcessor ，ApplicationContextAwareProcessor 本身是沒有擴展點的，但其內(nèi)部卻有7個擴展點可供實現(xiàn) ，分別為

• EnvironmentAware
• EmbeddedValueResolverAware
• ResourceLoaderAware
• ApplicationEventPublisherAware
• MessageSourceAware
• ApplicationStartupAware
• ApplicationContextAware

這些內(nèi)部擴展點觸發(fā)的時機在bean實例化之后，初始化之前。

1、EnvironmentAware：凡注冊到Spring容器內(nèi)的bean，實現(xiàn)了EnvironmentAware接口重寫setEnvironment方法后，在工程啟動時可以獲得application.properties的配置文件配置的屬性值。
2、EmbeddedValueResolverAware：用于獲取StringValueResolver的一個擴展類， StringValueResolver用于獲取基于String類型的properties的變量
3、ResourceLoaderAware：用于獲取ResourceLoader的一個擴展類，ResourceLoader可以用于獲取classpath內(nèi)所有的資源對象，可以擴展此類來拿到ResourceLoader對象。
4、ApplicationEventPublisherAware：用于獲取ApplicationEventPublisher的一個擴展類，ApplicationEventPublisher可以用來發(fā)布事件，結(jié)合ApplicationListener來共同使用
5、MessageSourceAware：用于獲取MessageSource的一個擴展類，MessageSource主要用來做國際化
6、ApplicationStartupAware：要開始收集定制的StartupStep，組件可以實現(xiàn)ApplicationStartupAware接口直接獲得ApplicationStartup實例或者在注入點請求ApplicationStartup類型。
7、ApplicationContextAware：可以用來獲取ApplicationContext的一個擴展類，也就是spring上下文管理器，可以手動的獲取任何在spring上下文注冊的bean

源碼分析

從下列源碼的invokeAwareInterfaces方法可知，ApplicationContextAwareProcessor關聯(lián)了大部分Spring內(nèi)置Aware接口,它們的執(zhí)行順序如
下源碼碼所示從上到下，最開始是EnvironmentAware，最后是ApplicationContextAware

package org.springframework.context.support;class ApplicationContextAwareProcessor implements BeanPostProcessor {private final ConfigurableApplicationContext applicationContext;private final StringValueResolver embeddedValueResolver;/*** Create a new ApplicationContextAwareProcessor for the given context.*/public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {this.applicationContext = applicationContext;this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());}@Override@Nullablepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware ||bean instanceof ApplicationStartupAware)) {return bean;}AccessControlContext acc = null;if (System.getSecurityManager() != null) {acc = this.applicationContext.getBeanFactory().getAccessControlContext();}if (acc != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {invokeAwareInterfaces(bean);return null;}, acc);}else {invokeAwareInterfaces(bean);}return bean;}private void invokeAwareInterfaces(Object bean) {if (bean instanceof EnvironmentAware) {((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());}if (bean instanceof EmbeddedValueResolverAware) {((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);}if (bean instanceof ResourceLoaderAware) {((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);}if (bean instanceof ApplicationEventPublisherAware) {((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);}if (bean instanceof MessageSourceAware) {((MessageSourceAware) bean).setMessageSource(this.applicationContext);}if (bean instanceof ApplicationStartupAware) {((ApplicationStartupAware) bean).setApplicationStartup(this.applicationContext.getApplicationStartup());}if (bean instanceof ApplicationContextAware) {((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);}}
}

示例代碼

示例一：擴展點的執(zhí)行順序

示例一展示的是7個內(nèi)部擴展點所執(zhí)行的順序

@Slf4j
@Configuration
public class ExtendInvokeAware implements EnvironmentAware, EmbeddedValueResolverAware, ResourceLoaderAware,ApplicationEventPublisherAware, MessageSourceAware, ApplicationStartupAware, ApplicationContextAware, BeanNameAware {@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {log.info("setApplicationContext--Extend--run {}",applicationContext);}@Overridepublic void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {log.info("setApplicationEventPublisher--Extend--run {}",applicationEventPublisher);}@Overridepublic void setApplicationStartup(ApplicationStartup applicationStartup) {log.info("setApplicationStartup--Extend--run {}",applicationStartup);}@Overridepublic void setEmbeddedValueResolver(StringValueResolver resolver) {log.info("setEmbeddedValueResolver--Extend--run {}",resolver);}@Overridepublic void setEnvironment(Environment environment) {log.info("setEnvironment--Extend--run {}",environment);}@Overridepublic void setMessageSource(MessageSource messageSource) {log.info("setMessageSource--Extend--run {}",messageSource);}@Overridepublic void setResourceLoader(ResourceLoader resourceLoader) {log.info("setResourceLoader--Extend--run {}",resourceLoader);}@Overridepublic void setBeanName(String name) {log.info("setBeanName--Extend--run {}",name);}
}

運行示例一

示例二：獲取配置文件值

展示如何利用實現(xiàn)EmbeddedValueResolverAware來獲取配置文件的屬性值

配置文件application.properties內(nèi)容

db.user=navicat
db.password=navicat
db.driverClass=com.mysql.jdbc.Driver

定義工具類ConfigUtil

該工具類功能為傳入的key獲取對應value

@Component
public class ConfigUtil implements EmbeddedValueResolverAware {private StringValueResolver resolver;@Overridepublic void setEmbeddedValueResolver(StringValueResolver resolver) {this.resolver = resolver;}/*** 獲取屬性，直接傳入屬性名稱即可* @param key* @return*/public String getPropertiesValue(String key) {StringBuilder name = new StringBuilder("${").append(key).append("}");return resolver.resolveStringValue(name.toString());}}

controller測試調(diào)用

@GetMapping("/testConfig")
public void testConfig() {String s = configUtil.getPropertiesValue("db.user");System.out.println(s);
}

運行示例二

示例三：實現(xiàn)ResourceLoaderAware讀取文件

ExtendResourceLoaderAware 文件內(nèi)容

實現(xiàn)ResourceLoaderAware 接口，并讀取文件內(nèi)容進行打印

@Slf4j
@Configuration
public class ExtendResourceLoaderAware implements ResourceLoaderAware {private ResourceLoader resourceLoader;@Overridepublic void setResourceLoader(ResourceLoader resourceLoader) {this.resourceLoader = resourceLoader;log.info("ApplicationContextAware--Extend--run {}",resourceLoader);}public void showResourceData() throws IOException{//This line will be changed for all versions of other examplesResource banner = resourceLoader.getResource("file:d:/token.json");InputStream in = banner.getInputStream();BufferedReader reader = new BufferedReader(new InputStreamReader(in));while (true) {String line = reader.readLine();if (line == null)break;System.out.println(line);}reader.close();}
}

token.json 文件

{"name":"張三"}

controller測試代碼

@Autowired
ApplicationContext context;@SuppressWarnings("resource")
@GetMapping("/testResource")
public void testResource() throws Exception{ExtendResourceLoaderAware extendResourceLoaderAware = (ExtendResourceLoaderAware) context.getBean("extendResourceLoaderAware");extendResourceLoaderAware.showResourceData();
}

運行示例三