Spring鉤子方法和鉤子接口的使用詳解
[TOC]
前言
SpringFramework其實(shí)具有很高的擴(kuò)展性，只是很少人喜歡挖掘那些擴(kuò)展點(diǎn)，而且官方的Refrence也很少提到那些Hook類或Hook接口，至于是不是Spring官方有意為之就不得而知。本文淺析一下筆者目前看到的Spring的一些對(duì)外開放的擴(kuò)展點(diǎn)、Hook接口或者Hook類，如果有什么錯(cuò)誤，希望多多交流指正，一切以Spring的源碼為準(zhǔn)，文章編寫使用的Spring版本為4.3.8.Release,對(duì)應(yīng)SpringBoot的版本為1.5.3.RELEASE
1、Aware接口族
Spring中提供了各種Aware接口，方便從上下文中獲取當(dāng)前的運(yùn)行環(huán)境，比較常見的幾個(gè)子接口有：
BeanFactoryAware,BeanNameAware,ApplicationContextAware,EnvironmentAware，BeanClassLoaderAware等，這些Aware的作用都可以從命名得知，并且其使用也是十分簡(jiǎn)單。
例如我們經(jīng)常看到SpringContext工具類：
@Component
public final class SpringContextAssisor implements ApplicationContextAware {
private static ApplicationContext applicationContext;
@Override
public 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);
}
}
實(shí)現(xiàn)ApplicationContextAware接口可以獲取ApplicationContext
又例如想獲取到當(dāng)前的一個(gè)Spring Bean的BeanFactory：
@Component
public class OneBean implements BeanFactoryAware {
private BeanFactory beanFactory;
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
}
一般來說，拿到的應(yīng)該是DefaultListableBeanFactory，因?yàn)檫@個(gè)BeanFactory是BeanFactory一族的最底層的BeanFactory實(shí)現(xiàn)類，擁有所有父BeanFactory的功能。
其他的Aware可以自己嘗試下功能。
PS：Aware是可以自定義擴(kuò)展的，具體可以參考下面這篇的博客：
http://www.cnblogs.com/RunForLove/p/5828916.html
2、InitializingBean接口和DisposableBean接口
InitializingBean接口只有一個(gè)方法#afterPropertiesSet，作用是：當(dāng)一個(gè)Bean實(shí)現(xiàn)InitializingBean，#afterPropertiesSet方法里面可以添加自定義的初始化方法或者做一些資源初始化操作(Invoked by a BeanFactory after it has set all bean properties supplied ==> "當(dāng)BeanFactory 設(shè)置完所有的Bean屬性之后才會(huì)調(diào)用#afterPropertiesSet方法")。
DisposableBean接口只有一個(gè)方法#destroy，作用是：當(dāng)一個(gè)單例Bean實(shí)現(xiàn)DisposableBean，#destroy可以添加自定義的一些銷毀方法或者資源釋放操作(Invoked by a BeanFactory on destruction of a singleton ==>"單例銷毀時(shí)由BeanFactory調(diào)用#destroy")
使用例子:
@Component
public class ConcreteBean implements InitializingBean,DisposableBean {
@Override
public void destroy() throws Exception {
System.out.println("釋放資源");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("初始化資源");
}
}
3、ImportBeanDefinitionRegistrar接口
功能：
先看官方的注釋
/**
* 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.
翻譯一下大概如下：
1.當(dāng)處理Java編程式配置類(使用了@Configuration的類)的時(shí)候，ImportBeanDefinitionRegistrar接口的實(shí)現(xiàn)類可以注冊(cè)額外的bean definitions;
2.ImportBeanDefinitionRegistrar接口的實(shí)現(xiàn)類必須提供給@Import注解或者是ImportSelector接口返回值
3.ImportBeanDefinitionRegistrar接口的實(shí)現(xiàn)類可能還會(huì)實(shí)現(xiàn)下面org.springframework.beans.factory.Aware接口中的一個(gè)或者多個(gè)，它們各自的方法優(yōu)先于ImportBeanDefinitionRegistrar#registerBeanDefinitions被調(diào)用
org.springframework.beans.factory.Aware的部分接口如下：
- org.springframework.context.EnvironmentAware(讀取或者修改Environment的變量)
- org.springframework.beans.factory.BeanFactoryAware (獲取Bean自身的Bean工廠)
- org.springframework.beans.factory.BeanClassLoaderAware(獲取Bean自身的類加載器)
- org.springframework.context.ResourceLoaderAware(獲取Bean自身的資源加載器)
個(gè)人理解：
1.首先需要自定義一個(gè)類去實(shí)現(xiàn)ImportBeanDefinitionRegistrar接口， #registerBeanDefinitions方法的參數(shù)有(使用了@Import的類型)元注解AnnotationMetadata以及BeanDefinitionRegistry(Bean注冊(cè)相關(guān)方法的提供接口)，通過BeanDefinitionRegistry的方法可以實(shí)現(xiàn)BeanDefinition注冊(cè)、移除等相關(guān)操作；
2.為了保證1生效，必須定義一個(gè)Java配置類(帶有注解@Configuration)通過@Import指定1中定義的實(shí)現(xiàn)類
一個(gè)例子：
目標(biāo)是通過自定義注解@EnableThrowable里面的targets屬性指定需要注冊(cè)進(jìn)去Spring容器的class，當(dāng)注解使用在@Configuration的類上，實(shí)現(xiàn)指定class的注冊(cè)，然后可以使用@Autowire實(shí)現(xiàn)自動(dòng)注入。
定義ImportBeanDefinitionRegistrar的實(shí)現(xiàn)類EnableThrowableRegistrar：
public class EnableThrowableRegistrar implements ImportBeanDefinitionRegistrar, EnvironmentAware {
@Override
public void setEnvironment(Environment environment) {
System.out.println("JAVA_HOME:" + environment.getProperty("JAVA_HOME"));
}
@Override
public 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);
}
}
}
}
定義一個(gè)注解@EnableThrowable：
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(value = {EnableThrowableRegistrar.class})
public @interface EnableThrowable {
Class<?>[] targets() default {};
}
定義一個(gè)Java配置類ConcreteConfiguration：
@Configuration
@EnableThrowable(targets = {ConcreteService.class})
public class ConcreteConfiguration {
}
定義一個(gè)非Spring管理的Service類ConcreteService：
public class ConcreteService {
public void sayHello(){
System.out.println("ConcreteService say hello!");
}
}
測(cè)試代碼：
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class ConcreteServiceTest {
@Autowired
private ConcreteService concreteService;
@Test
public void sayHello() throws Exception {
concreteService.sayHello();
}
}
結(jié)果：
可以看到讀取Environment屬性成功，同時(shí)普通Java類ConcreteService成功注冊(cè)到Spring容器并且自動(dòng)注入和調(diào)用成功。
4、BeanPostProcessor接口和BeanFactoryPostProcessor接口
一般我們叫這兩個(gè)接口為Spring的Bean后置處理器接口,作用是為Bean的初始化前后提供可擴(kuò)展的空間。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可以對(duì)bean的定義（配置元數(shù)據(jù)）進(jìn)行處理。也就是說，Spring IoC容器允許BeanFactoryPostProcessor在容器實(shí)際實(shí)例化任何其它的bean之前讀取配置元數(shù)據(jù)，并有可能修改它。如果你愿意，你可以配置多個(gè)BeanFactoryPostProcessor。你還能通過設(shè)置'order'屬性來控制BeanFactoryPostProcessor的執(zhí)行次序。(大概可以這樣理解:Spring容器加載了bean的定義文件之后，在bean實(shí)例化之前執(zhí)行的)
實(shí)現(xiàn)BeanPostProcessor接口可以在Bean(實(shí)例化之后)初始化的前后做一些自定義的操作，但是拿到的參數(shù)只有BeanDefinition實(shí)例和BeanDefinition的名稱，也就是無法修改BeanDefinition元數(shù)據(jù),這里說的Bean的初始化是：
1）bean實(shí)現(xiàn)了InitializingBean接口，對(duì)應(yīng)的方法為afterPropertiesSet
2）在bean定義的時(shí)候，通過init-method設(shè)置的方法
PS:BeanFactoryPostProcessor回調(diào)會(huì)先于BeanPostProcessor
使用例子：
實(shí)現(xiàn)一個(gè)BeanPostProcessor==>ConcreteBeanPostProcessor
@Order(1)
@Component
public class ConcreteBeanPostProcessor implements BeanPostProcessor {
@Override
public 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;
}
@Override
public 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;
}
}
實(shí)現(xiàn)一個(gè)BeanFactoryPostProcessor==>ConcreteBeanFactoryPostProcessor
@Component
public class ConcreteBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
BeanDefinition beanDefinition = beanFactory.getBeanDefinition("postBean");
MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
propertyValues.addPropertyValue("author", "throwable");
}
}
定義一個(gè)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));
}
}
測(cè)試類：
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class PostBeanTest {
@Autowired
private PostBean postBean;
@Test
public void sayhello() throws Exception {
postBean.sayhello();
}
}
結(jié)果：
PS:有興趣可以看下Spring內(nèi)置的一些實(shí)現(xiàn)了后置處理器接口的類，大概有下面這些：
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，既可以獲取和修改BeanDefinition的元數(shù)據(jù)，也可以實(shí)現(xiàn)BeanDefinition的注冊(cè)、移除等操作。
例子：
定義一個(gè)BeanDefinitionRegistryPostProcessor==>ConcreteBeanDefinitionRegistryPostProcessor
@Component
public class ConcreteBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
private static final String beanName = "concreteRPBean";
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
BeanDefinition beanDefinition = BeanDefinitionBuilder
.genericBeanDefinition(ConcreteRPBean.class)
.getBeanDefinition();
registry.registerBeanDefinition(beanName, beanDefinition);
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
propertyValues.addPropertyValue("author", "throwable");
}
}
定義一個(gè)普通的Java類：
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));
}
}
測(cè)試類：
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class ConcreteRPBeanTest {
@Autowired
private ConcreteRPBean concreteRPBean;
@Test
public void sayHello() throws Exception {
concreteRPBean.sayHello();
}
}
結(jié)果：
6、FactoryBean接口
首先第一眼要注意，是FactoryBean接口而不是BeanFactory接口。一般情況下，Spring通過反射機(jī)制利用bean的class屬性指定實(shí)現(xiàn)類來實(shí)例化bean ，實(shí)例化bean過程比較復(fù)雜。FactoryBean接口就是為了簡(jiǎn)化此過程，把bean的實(shí)例化定制邏輯下發(fā)給使用者。
在該接口中還定義了以下3個(gè)方法。
T getObject()：返回由FactoryBean創(chuàng)建的bean實(shí)例，如果isSingleton()返回true，則該實(shí)例會(huì)放到Spring容器中單實(shí)例緩存池中。
boolean isSingleton()：返回由FactoryBean創(chuàng)建的bean實(shí)例的作用域是singleton還是prototype。
Class<T> getObjectType()：返回FactoryBean創(chuàng)建的bean類型。
注意一點(diǎn)：通過Spring容器的getBean()方法返回的不是FactoryBean本身，而是FactoryBean#getObject()方法所返回的對(duì)象，相當(dāng)于FactoryBean#getObject()代理了getBean()方法。如果希望獲取CarFactoryBean的實(shí)例，則需要在使用getBean(beanName) 方法時(shí)在beanName前顯示的加上 "&" 前綴。
一個(gè)例子：
實(shí)體類：
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;
}
@Override
public String toString() {
return "Fruit{" +
"name='" + name + '\'' +
", color='" + color + '\'' +
'}';
}
}
自定義FactoryBean:
@Component
public class FruitFactoryBean implements FactoryBean<Fruit> {
@Override
public Fruit getObject() throws Exception {
Fruit fruit = new Fruit();
fruit.setColor("red");
fruit.setName("apple");
return fruit;
}
@Override
public Class<?> getObjectType() {
return Fruit.class;
}
@Override
public boolean isSingleton() {
return true;
}
}
測(cè)試類：
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class FruitFactoryBeanTest {
@Autowired
private FruitFactoryBean fruitFactoryBean;
@Autowired
private ApplicationContext applicationContext;
@Test
public void getObject() throws Exception {
//直接通過#getObject獲取實(shí)例
Fruit apple = fruitFactoryBean.getObject();
System.out.println(apple.toString());
//通過Spring上下文獲取實(shí)例
Fruit fruit = (Fruit) applicationContext.getBean("fruitFactoryBean");
System.out.println(fruit);
//獲取FruitFactoryBean自身的實(shí)例
FruitFactoryBean bean = (FruitFactoryBean) applicationContext.getBean("&fruitFactoryBean");
System.out.println(bean);
}
}
結(jié)果：
結(jié)果和預(yù)期一樣，通過ApplicationContext#getBean(beanName)獲取到的實(shí)際上是FactoryBean#getObject的實(shí)例，ApplicationContext#getBean(“&” + beanName)獲取到的才是FruitFactoryBean本身的實(shí)例。
7.ApplicationListener
ApplicationListener是一個(gè)接口，里面只有一個(gè)onApplicationEvent(E event)方法，這個(gè)泛型E必須是ApplicationEvent的子類，而ApplicationEvent是Spring定義的事件，繼承于EventObject，構(gòu)造要求必須傳入一個(gè)Object類型的source，這個(gè)source可以作為一個(gè)存儲(chǔ)對(duì)象。將會(huì)在ApplicationListener的onApplicationEvent里面得到回調(diào)。如果在上下文中部署一個(gè)實(shí)現(xiàn)了ApplicationListener接口的bean，那么每當(dāng)在一個(gè)ApplicationEvent發(fā)布到 ApplicationContext時(shí)，這個(gè)bean得到通知。其實(shí)這就是標(biāo)準(zhǔn)的Oberver設(shè)計(jì)模式。另外，ApplicationEvent的發(fā)布由ApplicationContext通過#publishEvent方法完成。其實(shí)這個(gè)實(shí)現(xiàn)從原理和代碼上看都有點(diǎn)像Guava的eventbus。
貼一個(gè)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> {
@Override
public 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());
}
}
測(cè)試類：
@SpringBootTest(classes = Application.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class EmailApplicationListenerTest {
@Autowired
private ApplicationContext applicationContext;
@Test
public void onApplicationEvent() throws Exception {
applicationContext.publishEvent(new EmailEvent("this is source",
"throwable","here is emailEvent","2017-5-16"));
}
}
控制臺(tái)輸出：
EmailApplicationListener callback!!
EmailEvent --> source: this is source
EmailEvent --> author: throwable
EmailEvent --> content: here is emailEvent
EmailEvent --> date: 2017-5-16
然后發(fā)覺簡(jiǎn)書竟然沒有markdown的[toc]，有點(diǎn)不方便，吐槽一下。
Updated on 2017-5-16 23:56.
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