Spring钩子方法和钩子接口的使用详解
前言
SpringFramework其实具有很高的扩展性,只是很少人喜欢挖掘那些扩展点,而且官方的Refrence也很少提到那些Hook类或Hook接口,至于是不是Spring官方有意为之就不得而知。本文浅析一下笔者目前看到的Spring的一些对外开放的扩展点、Hook接口或者Hook类,如果有什么错误,希望多多交流指正,一切以Spring的源码为准,文章编写使用的Spring版本为4.3.8.Release,对应SpringBoot的版本为1.5.3.RELEASE
1、Aware接口族
Spring中提供了各种Aware接口,方便从上下文中获取当前的运行环境,比较常见的几个子接口有:
BeanFactoryAware,BeanNameAware,ApplicationContextAware,EnvironmentAware,BeanClassLoaderAware等,这些Aware的作用都可以从命名得知,并且其使用也是十分简单。
例如我们经常看到SpringContext工具类:
@Component
public final class SpringContextAssisor implements ApplicationContextAware {private static ApplicationContext applicationContext;@Overridepublic void setApplicationContext(ApplicationContext applicationContext) {SpringContextAssisor.applicationContext = applicationContext;}public static Object getBeanDefinition(String name) {return applicationContext.getBean(name);}public static <T> T getBeanDefinition(String name, Class<T> clazz) {return applicationContext.getBean(name, clazz);}}
实现ApplicationContextAware接口可以获取ApplicationContext
又例如想获取到当前的一个Spring Bean的BeanFactory:
@Component
public class OneBean implements BeanFactoryAware {private BeanFactory beanFactory;@Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException {this.beanFactory = beanFactory;}
}
一般来说,拿到的应该是DefaultListableBeanFactory,因为这个BeanFactory是BeanFactory一族的最底层的BeanFactory实现类,拥有所有父BeanFactory的功能。
其他的Aware可以自己尝试下功能。
PS:Aware是可以自定义扩展的,具体可以参考下面这篇的博客:
http://www.cnblogs.com/RunForLove/p/5828916.html
2、InitializingBean接口和DisposableBean接口
InitializingBean接口只有一个方法#afterPropertiesSet,作用是:当一个Bean实现InitializingBean,#afterPropertiesSet方法里面可以添加自定义的初始化方法或者做一些资源初始化操作(Invoked by a BeanFactory after it has set all bean properties supplied ==> “当BeanFactory 设置完所有的Bean属性之后才会调用#afterPropertiesSet方法”)。
DisposableBean接口只有一个方法#destroy,作用是:当一个单例Bean实现DisposableBean,#destroy可以添加自定义的一些销毁方法或者资源释放操作(Invoked by a BeanFactory on destruction of a singleton ==>“单例销毁时由BeanFactory调用#destroy”)
使用例子:
@Component
public class ConcreteBean implements InitializingBean,DisposableBean {@Overridepublic void destroy() throws Exception {System.out.println("释放资源");}@Overridepublic void afterPropertiesSet() throws Exception {System.out.println("初始化资源");}
}
3、ImportBeanDefinitionRegistrar接口
功能:
先看官方的注释
/*** Interface to be implemented by types that register additional bean definitions when* processing @{@link Configuration} classes. Useful when operating at the bean definition* level (as opposed to {@code @Bean} method/instance level) is desired or necessary.** <p>Along with {@code @Configuration} and {@link ImportSelector}, classes of this type* may be provided to the @{@link Import} annotation (or may also be returned from an* {@code ImportSelector}).** <p>An {@link ImportBeanDefinitionRegistrar} may implement any of the following* {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective* methods will be called prior to {@link #registerBeanDefinitions}:* <ul>* <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>* <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}* <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}* <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}* </ul>** <p>See implementations and associated unit tests for usage examples.
翻译一下大概如下:
1.当处理Java编程式配置类(使用了@Configuration的类)的时候,ImportBeanDefinitionRegistrar接口的实现类可以注册额外的bean definitions;
2.ImportBeanDefinitionRegistrar接口的实现类必须提供给@Import注解或者是ImportSelector接口返回值
3.ImportBeanDefinitionRegistrar接口的实现类可能还会实现下面org.springframework.beans.factory.Aware接口中的一个或者多个,它们各自的方法优先于ImportBeanDefinitionRegistrar#registerBeanDefinitions被调用
org.springframework.beans.factory.Aware的部分接口如下:
org.springframework.context.EnvironmentAware(读取或者修改Environment的变量)
org.springframework.beans.factory.BeanFactoryAware (获取Bean自身的Bean工厂)
org.springframework.beans.factory.BeanClassLoaderAware(获取Bean自身的类加载器)
org.springframework.context.ResourceLoaderAware(获取Bean自身的资源加载器)
个人理解:
1.首先需要自定义一个类去实现ImportBeanDefinitionRegistrar接口, #registerBeanDefinitions方法的参数有(使用了@Import的类型)元注解AnnotationMetadata以及BeanDefinitionRegistry(Bean注册相关方法的提供接口),通过BeanDefinitionRegistry的方法可以实现BeanDefinition注册、移除等相关操作;
2.为了保证1生效,必须定义一个Java配置类(带有注解@Configuration)通过@Import指定1中定义的实现类
一个例子:
目标是通过自定义注解@EnableThrowable里面的targets属性指定需要注册进去Spring容器的class,当注解使用在@Configuration的类上,实现指定class的注册,然后可以使用@Autowire实现自动注入。
定义ImportBeanDefinitionRegistrar的实现类EnableThrowableRegistrar:
public class EnableThrowableRegistrar implements ImportBeanDefinitionRegistrar, EnvironmentAware {@Overridepublic void setEnvironment(Environment environment) {System.out.println("JAVA_HOME:" + environment.getProperty("JAVA_HOME"));}@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,BeanDefinitionRegistry registry) {Map<String, Object> annotationAttributes= importingClassMetadata.getAnnotationAttributes(EnableThrowable.class.getCanonicalName());Class<?>[] targets = (Class<?>[]) annotationAttributes.get("targets");if (null != targets && targets.length > 0) {for (Class<?> target : targets) {BeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition(target).getBeanDefinition();registry.registerBeanDefinition(beanDefinition.getBeanClassName(),beanDefinition);}}}
}
定义一个注解@EnableThrowable:
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(value = {EnableThrowableRegistrar.class})
public @interface EnableThrowable {Class<?>[] targets() default {};
}
定义一个Java配置类ConcreteConfiguration:
@Configuration
@EnableThrowable(targets = {ConcreteService.class})
public class ConcreteConfiguration {}
定义一个非Spring管理的Service类ConcreteService:
public class ConcreteService {public void sayHello(){System.out.println("ConcreteService say hello!");}
}
测试代码:
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class ConcreteServiceTest {@Autowiredprivate ConcreteService concreteService;@Testpublic void sayHello() throws Exception {concreteService.sayHello();}}
结果:
可以看到读取Environment属性成功,同时普通Java类ConcreteService成功注册到Spring容器并且自动注入和调用成功。
4、BeanPostProcessor接口和BeanFactoryPostProcessor接口
一般我们叫这两个接口为Spring的Bean后置处理器接口,作用是为Bean的初始化前后提供可扩展的空间。先看接口的方法:
BeanPostProcessor
public interface BeanPostProcessor {Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}
BeanFactoryPostProcessor
public interface BeanFactoryPostProcessor {void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}
BeanFactoryPostProcessor可以对bean的定义(配置元数据)进行处理。也就是说,Spring IoC容器允许BeanFactoryPostProcessor在容器实际实例化任何其它的bean之前读取配置元数据,并有可能修改它。如果你愿意,你可以配置多个BeanFactoryPostProcessor。你还能通过设置’order’属性来控制BeanFactoryPostProcessor的执行次序。(大概可以这样理解:Spring容器加载了bean的定义文件之后,在bean实例化之前执行的)
实现BeanPostProcessor接口可以在Bean(实例化之后)初始化的前后做一些自定义的操作,但是拿到的参数只有BeanDefinition实例和BeanDefinition的名称,也就是无法修改BeanDefinition元数据,这里说的Bean的初始化是:
1)bean实现了InitializingBean接口,对应的方法为afterPropertiesSet
2)在bean定义的时候,通过init-method设置的方法
PS:BeanFactoryPostProcessor回调会先于BeanPostProcessor
使用例子:
实现一个BeanPostProcessor==>ConcreteBeanPostProcessor
@Order(1)
@Component
public class ConcreteBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (beanName.contains("postBean"))System.out.println(String.format("Bean初始化之前,bean:%s,beanName:%s", bean.toString(), beanName));return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {if (beanName.contains("postBean"))System.out.println(String.format("Bean初始化之后,bean:%s,beanName:%s", bean.toString(), beanName));return bean;}
}
实现一个BeanFactoryPostProcessor==>ConcreteBeanFactoryPostProcessor
@Component
public class ConcreteBeanFactoryPostProcessor implements BeanFactoryPostProcessor {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {BeanDefinition beanDefinition = beanFactory.getBeanDefinition("postBean");MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();propertyValues.addPropertyValue("author", "throwable");}
}
定义一个Spring的Bean
@Component
public class PostBean {private String author;public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public void sayhello() {System.out.println(String.format("author %s say hello!", author));}
}
测试类:
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class PostBeanTest {@Autowiredprivate PostBean postBean;@Testpublic void sayhello() throws Exception {postBean.sayhello();}
}
结果:
PS:有兴趣可以看下Spring内置的一些实现了后置处理器接口的类,大概有下面这些:
AnnotationAwareAspectJAutoProxyCreator
AspectJAwareAdvisorAutoProxyCreator
InitDestroyAnnotationBeanPostProcessor
ApplicationContextAwareProcessor
AutowiredAnnotationBeanPostProcessor
CommonAnnotationBeanPostProcessor
RequiredAnnotationBeanPostProcessor
PersistenceAnnotationBeanPostProcessor
…
5、BeanDefinitionRegistryPostProcessor 接口
BeanDefinitionRegistryPostProcessor 接口可以看作是BeanFactoryPostProcessor和ImportBeanDefinitionRegistrar的功能集合,既可以获取和修改BeanDefinition的元数据,也可以实现BeanDefinition的注册、移除等操作。
例子:
定义一个BeanDefinitionRegistryPostProcessor==>ConcreteBeanDefinitionRegistryPostProcessor
@Component
public class ConcreteBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {private static final String beanName = "concreteRPBean";@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {BeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition(ConcreteRPBean.class).getBeanDefinition();registry.registerBeanDefinition(beanName, beanDefinition);}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();propertyValues.addPropertyValue("author", "throwable");}
}
定义一个普通的Java类:
public class ConcreteRPBean {private String author;public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public void sayHello(){System.out.println(String.format("ConcreteRPBean call sayhello method ==> author %s say hello!", author));}
}
测试类:
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class ConcreteRPBeanTest {@Autowiredprivate ConcreteRPBean concreteRPBean;@Testpublic void sayHello() throws Exception {concreteRPBean.sayHello();}}
结果:
6、FactoryBean接口
首先第一眼要注意,是FactoryBean接口而不是BeanFactory接口。一般情况下,Spring通过反射机制利用bean的class属性指定实现类来实例化bean ,实例化bean过程比较复杂。FactoryBean接口就是为了简化此过程,把bean的实例化定制逻辑下发给使用者。
在该接口中还定义了以下3个方法。
T getObject():返回由FactoryBean创建的bean实例,如果isSingleton()返回true,则该实例会放到Spring容器中单实例缓存池中。
boolean isSingleton():返回由FactoryBean创建的bean实例的作用域是singleton还是prototype。
Class getObjectType():返回FactoryBean创建的bean类型。
注意一点:通过Spring容器的getBean()方法返回的不是FactoryBean本身,而是FactoryBean#getObject()方法所返回的对象,相当于FactoryBean#getObject()代理了getBean()方法。如果希望获取CarFactoryBean的实例,则需要在使用getBean(beanName) 方法时在beanName前显示的加上 “&” 前缀。
一个例子:
实体类:
public class Fruit {private String name;private String color;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}@Overridepublic String toString() {return "Fruit{" +"name='" + name + '\'' +", color='" + color + '\'' +'}';}
}
自定义FactoryBean:
@Component
public class FruitFactoryBean implements FactoryBean<Fruit> {@Overridepublic Fruit getObject() throws Exception {Fruit fruit = new Fruit();fruit.setColor("red");fruit.setName("apple");return fruit;}@Overridepublic Class<?> getObjectType() {return Fruit.class;}@Overridepublic boolean isSingleton() {return true;}
}
测试类:
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class FruitFactoryBeanTest {@Autowiredprivate FruitFactoryBean fruitFactoryBean;@Autowiredprivate ApplicationContext applicationContext;@Testpublic void getObject() throws Exception {//直接通过#getObject获取实例Fruit apple = fruitFactoryBean.getObject();System.out.println(apple.toString());//通过Spring上下文获取实例Fruit fruit = (Fruit) applicationContext.getBean("fruitFactoryBean");System.out.println(fruit);//获取FruitFactoryBean自身的实例FruitFactoryBean bean = (FruitFactoryBean) applicationContext.getBean("&fruitFactoryBean");System.out.println(bean);}}
结果:
结果和预期一样,通过ApplicationContext#getBean(beanName)获取到的实际上是FactoryBean#getObject的实例,ApplicationContext#getBean(“&” + beanName)获取到的才是FruitFactoryBean本身的实例。
7.ApplicationListener
ApplicationListener是一个接口,里面只有一个onApplicationEvent(E event)方法,这个泛型E必须是ApplicationEvent的子类,而ApplicationEvent是Spring定义的事件,继承于EventObject,构造要求必须传入一个Object类型的source,这个source可以作为一个存储对象。将会在ApplicationListener的onApplicationEvent里面得到回调。如果在上下文中部署一个实现了ApplicationListener接口的bean,那么每当在一个ApplicationEvent发布到 ApplicationContext时,这个bean得到通知。其实这就是标准的Oberver设计模式。另外,ApplicationEvent的发布由ApplicationContext通过#publishEvent方法完成。其实这个实现从原理和代码上看都有点像Guava的eventbus。
贴一个例子:
EmailEvent:
public class EmailEvent extends ApplicationEvent {private String author;private String content;private String date;public EmailEvent(Object source, String author, String content, String date) {super(source);this.author = author;this.content = content;this.date = date;}public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}public String getDate() {return date;}public void setDate(String date) {this.date = date;}
}
EmailApplicationListener:
@Component
public class EmailApplicationListener implements ApplicationListener<EmailEvent> {@Overridepublic void onApplicationEvent(EmailEvent event) {System.out.println("EmailApplicationListener callback!!");System.out.println("EmailEvent --> source: " + event.getSource());System.out.println("EmailEvent --> author: " + event.getAuthor());System.out.println("EmailEvent --> content: " + event.getContent());System.out.println("EmailEvent --> date: " + event.getDate());}
}
测试类:
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class EmailApplicationListenerTest {@Autowiredprivate ApplicationContext applicationContext;@Testpublic void onApplicationEvent() throws Exception {applicationContext.publishEvent(new EmailEvent("this is source","throwable","here is emailEvent","2017-5-16"));}}
控制台输出:
EmailApplicationListener callback!!
EmailEvent --> source: this is source
EmailEvent --> author: throwable
EmailEvent --> content: here is emailEvent
EmailEvent --> date: 2017-5-16