俗話說得好“工欲善其事必先利其器”，現(xiàn)如今springboot與springcloud已成為快速構(gòu)建web應(yīng)用的利器。作為一個(gè)Java工程師，知道如下的spring擴(kuò)展點(diǎn)，可能會(huì)讓你編寫出擴(kuò)展性、維護(hù)性更高的代碼。

bean的生命周期

BeanFactoryPostProcessor接口

spring源碼中對(duì)該類功能描述如下： /*Factory hook that allows for custom modification of an application context's bean definitions, adapting the bean property values of the context's underlying bean factory.*/

翻譯過來的意思大致是：工廠鉤子允許自定義應(yīng)用上下文中的bean定義，調(diào)整上下文bean

工廠中bean的屬性值。直白點(diǎn)的意思就是允許修改bean定義的屬性值。

通過一個(gè)簡單的例子，來了解下鉤子的簡單應(yīng)用：定義一個(gè)類GoodEntity和DemoBeanFactoryProcessor。自定義的DemoBeanFactoryProcessor功能很簡單就是從BeanFactory中獲取goodEntity的bean定義，然后設(shè)置了goodentity的name屬性值。

@Slf4j @Component @Data public class GoodEntity {private String name;} @Component public class DemoBeanFactoryProcessor implements BeanFactoryPostProcessor {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {BeanDefinition goodEntity = beanFactory.getBeanDefinition("goodEntity");goodEntity.getPropertyValues().addPropertyValue("name", "測(cè)試設(shè)置貨品名稱");} } @SpringBootApplication public class CourseApplication {public static void main(String[] args) {ConfigurableApplicationContext run = SpringApplication.run(CourseApplication.class, args);System.err.println(run.getBean(GoodEntity.class).getName());} }

輸出結(jié)果如下，可以到打印出了我們?cè)O(shè)置name屬性值。

2021-01-15 15:33:28.818 INFO 7112 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/mall] : Initializing Spring embedded WebApplicationContext 2021-01-15 15:33:28.818 INFO 7112 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 819 ms 2021-01-15 15:33:28.943 INFO 7112 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor' 2021-01-15 15:33:29.054 INFO 7112 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '/mall' 2021-01-15 15:33:29.062 INFO 7112 --- [ main] c.i.s.s.course.CourseApplication : Started CourseApplication in 1.409 seconds (JVM running for 2.186) 測(cè)試設(shè)置貨品名稱

PS:通常情況下如果對(duì)兩個(gè)bean的初始化順序有要求，我們可以通過BeanDefinition的setDependsOn，來保證兩個(gè)Bean的初始順序。

BeanDefinitionRegistryPostProcessor接口

該接口是BeanFactoryPostProcessor的擴(kuò)展接口，允許在普通的BeanFactoryPostProcessor生效前，向beanfactory中注冊(cè)BeanDefinition。通過一段代碼我們了解下該接口的作用

@Component public class DemoBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {String beanClassName = OrderEntity.class.getName();AbstractBeanDefinition beanDefinition =BeanDefinitionBuilder.genericBeanDefinition(beanClassName).getBeanDefinition();beanDefinition.getPropertyValues().addPropertyValue("orderId", "id-0001");String beanName = AnnotationBeanNameGenerator.INSTANCE.generateBeanName(beanDefinition, registry);registry.registerBeanDefinition(beanName, beanDefinition);}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {} } @Data @Builder @NoArgsConstructor @AllArgsConstructor public class OrderEntity implements Serializable {private String orderId;private String address;private List<GoodEntity> goods;private LocalDateTime createTime;private String userId;private Integer pay;private BigDecimal cost;} @SpringBootApplication public class CourseApplication {public static void main(String[] args) {ConfigurableApplicationContext run = SpringApplication.run(CourseApplication.class, args);System.err.println(run.getBean(OrderEntity.class).getOrderId());} }

大致意思是通過DemoBeanDefinitionRegistryPostProcessor向beanfactory中注冊(cè)bean定義，然后從spring容器中獲取該bean，打印屬性。

BeanPostProcessor接口

源碼中對(duì)該類的描述 /*Factory hook that allows for custom modification of new bean instances —for example, checking for marker interfaces or wrapping beans with proxies.*/

翻譯過來的大致意思是：工廠鉤子允許自定義修改新的bean實(shí)例，例如檢查標(biāo)記的接口或者使用代理包裹bean。下面我們通過代碼來看看該鉤子的作用，before修改orderid，after打印。

@Component public class DemoBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (bean instanceof OrderEntity) {OrderEntity entity = (OrderEntity)bean;System.err.println("before");System.err.println("orderId " + entity.getOrderId());entity.setOrderId("id-0002");}return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {if (bean instanceof OrderEntity) {OrderEntity entity = (OrderEntity)bean;System.err.println("after");System.err.println("orderId " + entity.getOrderId());}return bean;} }

輸出結(jié)果如下：

2021-01-15 17:41:17.783 INFO 9488 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor' before orderId id-0001 after orderId id-0002 2021-01-15 17:41:17.904 INFO 9488 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '/mall' 2021-01-15 17:41:17.912 INFO 9488 --- [ main] c.i.s.s.course.CourseApplication : Started

PS:感興趣的朋友可以看看，spring的aop生成代理對(duì)象就是依賴該鉤子完成的。

Aware接口

• BeanFactoryAware —— 獲取BeanFactory對(duì)象

• BeanClassLoaderAware —— 獲取加載Bean的ClassLoader

• BeanNameAware —— 獲取beanName

• ApplicationContextAware —— 獲取ApplicationContext

• EnvironmentAware —— 獲取spring的上下文環(huán)境Environment

看看具體的示例：

@Slf4j @Component @Data public class DemoAwareimplements BeanFactoryAware, BeanClassLoaderAware, BeanNameAware, ApplicationContextAware, EnvironmentAware {private ClassLoader classLoader;private BeanFactory beanFactory;private String name;private ApplicationContext applicationContext;private Environment environment;@Overridepublic void setBeanClassLoader(ClassLoader classLoader) {this.classLoader = classLoader;log.info("classloader {}", classLoader.getClass());}@Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException {this.beanFactory = beanFactory;log.info("beanFactory {}", beanFactory.getClass());}@Overridepublic void setBeanName(String name) {this.name = name;log.info("name {}", name);}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {this.applicationContext = applicationContext;log.info("applicationContext {}", applicationContext.getClass());}@Overridepublic void setEnvironment(Environment environment) {this.environment = environment;log.info("environment {}", environment.getClass());}}

PS:這些個(gè)Aware我個(gè)人最喜歡用的是ApplicationContextAware和EnvironmentAware。可以獲取Spring的上下文和Spring運(yùn)行時(shí)的環(huán)境配置信息，就可以隨意獲取bean和環(huán)境配置信息了。

InitializingBean接口

spring中對(duì)該接口功能的描述 /* Interface to be implemented by beans that need to react once all their propertieshave been set by a {@link BeanFactory}: e.g. to perform custom initialization,or merely to check that all mandatory properties have been set*/

翻譯過來的意思大致是：實(shí)現(xiàn)該接口的bean，會(huì)在所有的屬性都被（BeanFactory）設(shè)置完成后執(zhí)行。例如，實(shí)現(xiàn)自定義的初始化，或者檢查必要的屬性是否被設(shè)置了。

@Component public class DemoInitializingBean implements InitializingBean {@Autowiredprivate OrderEntity orderEntity;private String name;@Overridepublic void afterPropertiesSet() throws Exception {if (orderEntity != null) {System.out.println("setted");}name = "already";} }

總結(jié)

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