SpringBoot-将Bean放入容器的五种方式

@Configuration
public class MyConfiguration {@Beanpublic Person person() {Person person = new Person();person.setName("spring");return person;}
}

2、@Componet + @ComponentScan

@Component
public class Person {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Person{" +"name='" + name + '\'' +'}';}
}@ComponentScan(basePackages = "com.springboot.initbean.*")
public class Demo1 {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}

3、@Import注解导入

@import注解源码

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {/**   * 用于导入一个class文件     * {@link Configuration @Configuration}, {@link ImportSelector},     * {@link ImportBeanDefinitionRegistrar}, or regular component classes to import.     */Class<?>[] value();}

3.1、直接使用@import注解导入类

然后自动的就被放置在IOC容器中了。

public class Person {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Person{" +"name='" + name + '\'' +'}';}
}
/*** 直接使用@Import导入person类，然后尝试从applicationContext中取，成功拿到**/
@Import(Person.class)
public class Demo1 {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}

3.2 @Import + ImportSelector

@Import(MyImportSelector.class)
public class Demo1 { public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}class MyImportSelector implements ImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata importingClassMetadata) {return new String[]{"com.springboot.pojo.Person"};}
}

3.3 @Import + ImportBeanDefinitionRegistrar

bean的定义(bean的元数据)，也是需要放在IOC容器中进行管理的，先有bean的元数据，

applicationContext再根据bean的元数据去创建Bean。

@Import(MyImportBeanDefinitionRegistrar.class)
public class Demo1 {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// 构建一个beanDefinition, 关于beanDefinition我后续会介绍，可以简单理解为bean的定义.AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Person.class).getBeanDefinition();// 将beanDefinition注册到Ioc容器中.registry.registerBeanDefinition("person", beanDefinition);}
}

3.4 @Import + DeferredImportSelector

DeferredImportSelector 它是 ImportSelector 的子接口，所以实现的方法和第二种无异。

只是Spring的处理方式不同，它和Spring Boot中的自动导入配置文件 延迟导入有关

@Import(MyDeferredImportSelector.class)
public class Demo1 {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}
class MyDeferredImportSelector implements DeferredImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata importingClassMetadata) {// 也是直接将Person的全限定名放进去return new String[]{Person.class.getName()};}
}

4、使用FactoryBean接口

FactoryBean, 后缀为bean，那么它其实就是一个bean,

BeanFactory，顾名思义 bean工厂，它是IOC容器的顶级接口

@Configuration
public class Demo1 {@Beanpublic PersonFactoryBean personFactoryBean() {return new PersonFactoryBean();}public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}class PersonFactoryBean implements FactoryBean<Person> {/**     *  直接new出来Person进行返回.     */@Overridepublic Person getObject() throws Exception {return new Person();}/**     *  指定返回bean的类型.     */@Overridepublic Class<?> getObjectType() {return Person.class;}
}

5、使用 BeanDefinitionRegistryPostProcessor

等beanDefinition加载完毕之后，对beanDefinition进行后置处理，

可以在此进行调整IOC容器中的beanDefinition，从而干扰到后面进行初始化bean。

public class Demo1 {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();MyBeanDefinitionRegistryPostProcessor beanDefinitionRegistryPostProcessor = new MyBeanDefinitionRegistryPostProcessor();applicationContext.addBeanFactoryPostProcessor(beanDefinitionRegistryPostProcessor);applicationContext.refresh();Person bean = applicationContext.getBean(Person.class);System.out.println(bean);}
}class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Person.class).getBeanDefinition();registry.registerBeanDefinition("person", beanDefinition);}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
}