俗话说得好“工欲善其事必先利其器”，现如今springboot与springcloud已成为快速构建web应用的利器。作为一个Java工程师，知道如下的spring扩展点，可能会让你编写出扩展性、维护性更高的代码。

bean的生命周期

BeanFactoryPostProcessor接口

spring源码中对该类功能描述如下：
/*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.*/

翻译过来的意思大致是：工厂钩子允许自定义应用上下文中的bean定义，调整上下文bean

工厂中bean的属性值。直白点的意思就是允许修改bean定义的属性值。

通过一个简单的例子，来了解下钩子的简单应用：定义一个类GoodEntity和DemoBeanFactoryProcessor。自定义的DemoBeanFactoryProcessor功能很简单就是从BeanFactory中获取goodEntity的bean定义，然后设置了goodentity的name属性值。

@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", "测试设置货品名称");}
}
@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());}
}

输出结果如下，可以到打印出了我们设置name属性值。

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)
测试设置货品名称

PS:通常情况下如果对两个bean的初始化顺序有要求，我们可以通过BeanDefinition的setDependsOn，来保证两个Bean的初始顺序。

BeanDefinitionRegistryPostProcessor接口

该接口是BeanFactoryPostProcessor的扩展接口，允许在普通的BeanFactoryPostProcessor生效前，向beanfactory中注册BeanDefinition。通过一段代码我们了解下该接口的作用

@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());}
}

大致意思是通过DemoBeanDefinitionRegistryPostProcessor向beanfactory中注册bean定义，然后从spring容器中获取该bean，打印属性。

BeanPostProcessor接口

源码中对该类的描述
/*Factory hook that allows for custom modification of new bean instances —for example, checking for marker interfaces or wrapping beans with proxies.*/

翻译过来的大致意思是：工厂钩子允许自定义修改新的bean实例，例如检查标记的接口或者使用代理包裹bean。下面我们通过代码来看看该钩子的作用，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;}
}

输出结果如下：

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:感兴趣的朋友可以看看，spring的aop生成代理对象就是依赖该钩子完成的。

Aware接口

• BeanFactoryAware —— 获取BeanFactory对象

• BeanClassLoaderAware —— 获取加载Bean的ClassLoader

• BeanNameAware —— 获取beanName

• ApplicationContextAware —— 获取ApplicationContext

• EnvironmentAware —— 获取spring的上下文环境Environment

看看具体的示例：

@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:这些个Aware我个人最喜欢用的是ApplicationContextAware和EnvironmentAware。可以获取Spring的上下文和Spring运行时的环境配置信息，就可以随意获取bean和环境配置信息了。

InitializingBean接口

spring中对该接口功能的描述
/* 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*/

翻译过来的意思大致是：实现该接口的bean，会在所有的属性都被（BeanFactory）设置完成后执行。例如，实现自定义的初始化，或者检查必要的属性是否被设置了。

@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";}
}