Spring容器注入bean的五种方法逐个解析

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import org.springframework.context.annotation.ComponentScan;

@ComponentScan (basePackages = "com.gs.beanRegister" )

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext(BootStrap. class );

         A bean = context.getBean(A. class );

         bean.say();

     }

}

import org.springframework.stereotype.Component;

@Component

public class A {

     public void say() {

         System.out.println( "这是a" );

     }

}

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Bean;

@Configuration

public class MyConfiguration {

     @Bean

     public A a() {

         return new A();

     }

}

import org.springframework.context.annotation.Import;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

@Import (A. class )

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext(BootStrap. class );

         A bean = context.getBean(A. class );

         //B bean = context.getBean(B.class);

         bean.say();

     }

}

public class A {

     public void say() {

         System.out.println( "这是a" );

     }

}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import org.springframework.context.annotation.Import;

@Import (MyConfiguration. class )

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext(BootStrap. class );

         A bean = context.getBean(A. class );

         bean.say();

     }

}

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

// 使用@Import导入配置类时，@Configuration可以不加

//@Configuration

public class MyConfiguration {

     @Bean

     public A a() {

         return new A();

     }

}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import org.springframework.context.annotation.Import;

@Import (MyImportSelector. class )

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext(BootStrap. class );

         A bean = context.getBean(A. class );

         bean.say();

     }

}

import org.springframework.context.annotation.ImportSelector;

import org.springframework.core.type.AnnotationMetadata;

public class MyImportSelector implements ImportSelector {

     @Override

     public String[] selectImports(AnnotationMetadata metadata) {

         // 返回要注入的bean的全路径，A类不用任何注解修饰

         // SpringBoot的自动装配，就用到了这种方式：

         // 返回配置类的全路径，配置类的@Bean方法返回的对象也能注入到容器中

         return new String[] { A. class .getName() };

     }

}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import org.springframework.context.annotation.Import;

@Import (MyImportBeanDefinitionRegistrar. class )

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext(BootStrap. class );

         A bean = context.getBean(A. class );

         bean.say();

     }

}

import org.springframework.beans.factory.config.BeanDefinition;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;

import org.springframework.beans.factory.support.RootBeanDefinition;

import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;

import org.springframework.core.type.AnnotationMetadata;

public class MyImportBeanDefinitionRegistrar implements

              ImportBeanDefinitionRegistrar {

     @Override

     public void registerBeanDefinitions(AnnotationMetadata metadata,

                 BeanDefinitionRegistry registry) {

         // 构建bean的元数据，A类不用任何注解修饰

         // spring-mybatis扫描mapper接口，生成代理类，就是用的这种方式

         BeanDefinition definition = new RootBeanDefinition(A. class );

         registry.registerBeanDefinition( "a" , definition);

     }

}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import org.springframework.context.annotation.Import;

@Import (MyFactoryBean. class )

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext(BootStrap. class );

         A bean = context.getBean(A. class );

         bean.say();

     }

}

import org.springframework.beans.factory.FactoryBean;

public class MyFactoryBean implements FactoryBean {

     @Override

     public Object getObject() throws Exception {

         return new A();

     }

     @Override

     public Class<?> getObjectType() {

         return A. class ;

     }

}

import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class BootStrap {

     public static void main(String[] args) {

         AnnotationConfigApplicationContext context =

         new AnnotationConfigApplicationContext();

         BeanDefinitionRegistryPostProcessor postProcessor =

         new MyBeanDefinitionRegistryPostProcessor();

         context.addBeanFactoryPostProcessor(postProcessor);

         context.refresh();

         A a = context.getBean(A. class );

         a.say();

     }

}

import org.springframework.beans.BeansException;

import org.springframework.beans.factory.config.BeanDefinition;

import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;

import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;

import org.springframework.beans.factory.support.RootBeanDefinition;

public class MyBeanDefinitionRegistryPostProcessor implements

              BeanDefinitionRegistryPostProcessor {

     @Override

     public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry

                 registry) throws BeansException {

         BeanDefinition definition = new RootBeanDefinition(A. class );

         registry.registerBeanDefinition( "a" , definition);

     }

     @Override

     public void postProcessBeanFactory(ConfigurableListableBeanFactory

                 beanFactory) throws BeansException {

     }

}