條條大路通羅馬
前提：怕讀者沒有頭緒，請在https://blog.csdn.net/dong19891210/article/details/105697175的情況下看
Spring bean有以下幾種注冊方式：
1. 通過GenericBeanDefinition注冊
示例代碼：
消息輔助類
public class Message { private String message; public String getMessage() { return message; } public void setMessage(String message) { this.message = message; } public void print() { System.out.println("消息是: " + message); } }
注冊測試類：
/** * * @author dgm * @describe "GenericBeanDefinition注冊bean定義" * @date 2020年4月27日 */ public class GenericBeanDefinitionExample { public static void main (String[] args) { DefaultListableBeanFactory context = new DefaultListableBeanFactory(); //在此構造bean定義 GenericBeanDefinition gbd = new GenericBeanDefinition(); gbd.setBeanClass(Message.class); // MutablePropertyValues mpv = new MutablePropertyValues(); mpv.add("message", "this is a bean"); //注冊到環境上下文 context.registerBeanDefinition("myBean", gbd); Message bean = context.getBean(Message.class); bean.print(); Message myBean = (Message) context.getBean("myBean"); myBean.print(); } }結果：
2. 通過BeanDefinitionBuilder注冊
/** * * @author dgm * @describe "" * @date 2020年4月16日 */ public class BeanDefinitionBuilderExample { public static void main (String[] args) { DefaultListableBeanFactory context = new DefaultListableBeanFactory(); //用到了構建者模式 BeanDefinitionBuilder b = BeanDefinitionBuilder.rootBeanDefinition(Message.class) .addPropertyValue("message", "this is a bean"); context.registerBeanDefinition("myBean", b.getBeanDefinition()); Message bean = context.getBean(Message.class); bean.print(); Message myBean = (Message) context.getBean("myBean"); myBean.print(); } } 效果同第一種情況，只是用的是BeanDefinitionBuilder模式
3. 通過BeanFactoryPostProcessor
public class MessageBeanFactoryPostProcessor implements BeanFactoryPostProcessor { @Override public void postProcessBeanFactory( ConfigurableListableBeanFactory beanFactory) throws BeansException { // TODO Auto-generated method stub GenericBeanDefinition gbd = new GenericBeanDefinition(); gbd.setBeanClass(Message.class); MutablePropertyValues mpv = new MutablePropertyValues(); mpv.add("message", "this is a BeanFactoryPostProcessor bean"); gbd.setPropertyValues(mpv); ((DefaultListableBeanFactory) beanFactory).registerBeanDefinition( "myBean", gbd); } } 配置類
@Configuration public class MyConfig { @Bean MessageBeanFactoryPostProcessor messageConfigBean () { return new MessageBeanFactoryPostProcessor(); } }測試類：
/** * * @author dgm * @describe "測試BeanFactoryPostProcessor" * @date 2020年4月27日 */ public class BeanFactoryPostProcessorExample { public static void main (String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class); //MyBean bean = context.getBean(MyBean.class); //bean.doSomething(); //bean.doOtherSomething(); Message bean = context.getBean(Message.class); bean.print(); Message myBean = (Message) context.getBean("myBean"); myBean.print(); } } 效果：
4. 通過BeanDefinitionRegistryPostProcessor
public class MessageBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor { @Override public void postProcessBeanFactory( ConfigurableListableBeanFactory beanFactory) throws BeansException { // TODO Auto-generated method stub } @Override public void postProcessBeanDefinitionRegistry( BeanDefinitionRegistry registry) throws BeansException { // TODO Auto-generated method stub GenericBeanDefinition gbd = new GenericBeanDefinition(); gbd.setBeanClass(Message.class); MutablePropertyValues mpv = new MutablePropertyValues(); mpv.add("message", "this is a BeanDefinitionRegistryPostProcessor bean"); gbd.setPropertyValues(mpv); registry.registerBeanDefinition( "myBean", gbd); } } 配置類
@Configuration public class MyConfig { @Bean ConfigBeanFactoryPostProcessor myConfigBean () { return new ConfigBeanFactoryPostProcessor(); } /*@Bean MessageBeanFactoryPostProcessor messageBeanFactoryPostProcessor () { return new MessageBeanFactoryPostProcessor(); }*/ @Bean MessageBeanDefinitionRegistryPostProcessor messageBeanDefinitionRegistryPostProcessor () { return new MessageBeanDefinitionRegistryPostProcessor(); } } 測試類：
public class BeanDefinitionRegistryPostProcessorExample { public static void main (String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class); //MyBean bean = context.getBean(MyBean.class); //bean.doSomething(); //bean.doOtherSomething(); Message bean = context.getBean(Message.class); bean.print(); Message myBean = (Message) context.getBean("myBeanDefinitionRegistry"); myBean.print(); } } 效果：
5. 通過Import
import類型有以下幾類：
5.1 ImportSelector導入
public interface PrintService { void print(String msg); } public class PrintServiceImpl implements PrintService{ @Override public void print(String msg) { System.out.println("Hello : " + msg); } } //重點，實現了ImportSelector public class MessageImportSelector implements ImportSelector { @Override public String[] selectImports(AnnotationMetadata importingClassMetadata) { // TODO Auto-generated method stub return new String[] {PrintServiceImpl.class.getName()}; } } //配置類 @Configuration @Import(MessageImportSelector.class) public class MessageImportSelectorConfiguration { } 測試代碼和效果：
注：我是以demo演示（selectImports()寫死了），實際場景中可以動態注入bean，想象空間很大。
5.2 ImportBeanDefinitionRegistrar注冊
/** * * @author dgm * @describe "實現ImportBeanDefinitionRegistrar " * @date 2020年4月28日 */ public class MessageImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar { @Override public void registerBeanDefinitions( AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { // 只以演示為例，現實場景通過importingClassMetadata拿到動態數據 GenericBeanDefinition gbd = new GenericBeanDefinition(); gbd.setBeanClass(Message.class); MutablePropertyValues mpv = new MutablePropertyValues(); mpv.add("message", "this is a ImportBeanDefinitionRegistrar bean"); gbd.setPropertyValues(mpv); registry.registerBeanDefinition("myBean", gbd); GenericBeanDefinition printBeanDefinition = new GenericBeanDefinition(); printBeanDefinition.setBeanClass(PrintServiceImpl.class); registry.registerBeanDefinition("printBean", printBeanDefinition); } }配置類：
@Configuration @Import(MessageImportBeanDefinitionRegistrar.class) public class MessageImportBeanDefinitionRegistrarConfiguration { } 測試
/** * * @author dgm * @describe "測試ImportBeanDefinitionRegistrar" * @date 2020年4月28日 */ public class ImportBeanDefinitionRegistrarDemo { public static void main(String[] args) { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext( MessageImportBeanDefinitionRegistrarConfiguration.class); String[] beanNames = applicationContext.getBeanDefinitionNames(); System.out.println(Arrays.asList(beanNames)); Message bean = applicationContext.getBean(Message.class); bean.print(); PrintService ps = (PrintService) applicationContext .getBean(PrintService.class); ps.print("ImportBeanDefinitionRegistrar demo"); } } 
5.3 組合式，比如kafak集成到spring
/** * * @author dgm * @describe "實現了ImportSelector接口的導入" * @date 2020年4月28日 */ public class MessageImportSelector implements ImportSelector { @Override public String[] selectImports(AnnotationMetadata importingClassMetadata) { // TODO Auto-generated method stub //return new String[] {PrintServiceImpl.class.getName()}; //不再寫死了，用上元數據 Map<String, Object> annotationAttributes = importingClassMetadata.getAnnotationAttributes(PrintServiceScan.class.getName()); String[] basePackages = (String[]) annotationAttributes.get("basePackages"); if (basePackages == null || basePackages.length == 0) {//PrintServiceScan的basePackages默認為空數組 String basePackage = null; try { basePackage = Class.forName(importingClassMetadata.getClassName()).getPackage().getName(); } catch (ClassNotFoundException e) { e.printStackTrace(); } basePackages = new String[] {basePackage}; } ClassPathScanningCandidateComponentProvider scanner = new ClassPathScanningCandidateComponentProvider(false); TypeFilter printServiceFilter = new AssignableTypeFilter(PrintService.class); scanner.addIncludeFilter(printServiceFilter); Set<String> classes = new HashSet<>(); for (String basePackage : basePackages) { scanner.findCandidateComponents(basePackage).forEach(beanDefinition -> classes.add(beanDefinition.getBeanClassName())); } return classes.toArray(new String[classes.size()]); } }@Documented @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE) @Import(MessageImportSelector.class) public @interface PrintServiceScan { @AliasFor("value") String[] basePackages() default {}; @AliasFor("basePackages") String[] value() default {}; }
/** * * @author dgm * @describe "" * @date 2020年4月28日 */ @Configuration //@Import(MessageImportSelector.class) @PrintServiceScan("spring.service.impl") public class MessageImportSelectorConfiguration { } import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; import org.springframework.context.annotation.Import; import org.springframework.stereotype.Indexed; import spring.config.MessageImportSelectorConfiguration; @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(MessageImportSelectorConfiguration.class) public @interface EnablePrintService { } 最終測試：
/** * * @author dgm * @describe "測試組合式ImportSelector" * @date 2020年4月28日 */ public class ImportSelectorDemo { public static void main(String[] args) { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MessageImportSelectorConfiguration.class); PrintService ps = (PrintService) applicationContext.getBean(PrintService.class); ps.print("組合式 ImportSelector demo"); } } 
附詳情參考源碼ConfigurationClassParser類處理如何處理不同的import
總結：我是層層遞進寫的，spring bean 注冊幾種方式：GenericBeanDefinition，BeanDefinitionBuilder（設計模式無處不在），BeanFactoryPostProcessor，BeanDefinitionRegistryPostProcessor，Import型。
靈活性很強，很難達成統一（連交通規矩都難一統，更何況這），條條大路通羅馬，沒有最好只有合適，如果讓你選擇注冊bean或擴展性開發或集成第三方，你會選哪種呢，可以參考mybatis（用ImportBeanDefinitionRegister注冊） ，activemq，kafak組合式，dubbo，redis等，甚至spring aop也算是bean的注冊(用了其他的方式注冊進來)擴展，也包括Spring Boot里@SpringBootApplication，springboot也是spring bean的擴展開發，不是嗎！！！決定已知性的bean可寫死注冊，不確定性的最好可配置性組合。搞懂了Spring bean及衍生品（就像金融衍生品一樣），就搞懂了90%中國軟件開發java領域業務技術的方向
參考：
1. BeanDefinitionBuilder.java https://alvinalexander.com/java/jwarehouse/spring-framework-2.5.3/src/org/springframework/beans/factory/support/BeanDefinitionBuilder.java.shtml
2. bean definition for automatic FilterRegistrationBeanFactory http://dimafeng.com/2015/11/27/dynamic-bean-definition/
3. 使用@import導入實現了ImportBeanDefinitionRegistrar接口的類 https://blog.51cto.com/14672031/2474904
4. Spring向容器注冊Bean的高級應用 https://cloud.tencent.com/developer/article/1497795
5. How to integrate Jdon Framework with Spring http://en.jdon.com/springIntegration.html
6. Spring Boot dynamically injects beans through importbeandefinitionregister
7. Spring - Using ImportBeanDefinitionRegistrar
https://www.logicbig.com/tutorials/spring-framework/spring-core/import-bean-registrar.html
10. Spring - Dynamically register beans https://www.logicbig.com/tutorials/spring-framework/spring-core/bean-definition.html