springBoot bean的多种加载方式

加载方式"/>

springBoot bean的多种加载方式

1、通过xml

2、通过注解@Component及其衍生注解@Controller、@Service、@Repository定义bean

    例子：

        @Component

       public void Car{

       }

3、使用@Configuration定义成一个配置类

     @Configuration

      public void Car{

       }

4、实现FactoryBean

       例子：        

public class Car {
}

public class CarFactoryBean implements FactoryBean<Car> {@Overridepublic Car getObject() throws Exception {Car car = new Car();//创建这个bean前，在这边可以自定义处理一些业务逻辑return car;}@Overridepublic Class<?> getObjectType() {return Car.class;}@Overridepublic boolean isSingleton() {return FactoryBean.super.isSingleton();}
}

@Configuration
public class SpConfig {@Beanpublic CarFactoryBean car(){return new CarFactoryBean();}
}

5、加载配置类并加载配置文件

例子：

public class Car {
}

app.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns=""xmlns:xsi=""xsi:schemaLocation=" .xsd"><bean id="car" class="com.melax.ailatest.bean.Car"></bean>
</beans>

@Configuration
@ImportResource("app.xml")
public class SpConfig2 {}

6、使用@Import注解方式导入，被导入的bean无需使用注解申明为bean

public class Car {
}

@Import({Car.class})
public class SpConfig3 {}

7、导入实现了ImportSelector接口的类，实现了对导入源的编程时处理

示例：

public class Car {
}

public class MyImportSelector implements ImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata importingClassMetadata) {//各种条件判断boolean b = importingClassMetadata.hasAnnotation("org.springframework.context.annotation.Import");System.out.println("flag:"+b);if (b){return new String[]{"com.melax.ailatest.bean.car"};}else {return new String[0];}}
}

@Import({MyImportSelector.class})
public class SpConfig4 {}

8、导入实现了ImportBeanDefinitionRegistrar接口的类，通过BeanDefinition注册器注册实名bean,实现对容器中bean的裁定，例如对现有bean的覆盖，进而达成不修改源代码的情况下更换实现的效果

public class Car {
}

public class Dog {
}

public class MyImportBeanDefinition implements ImportBeanDefinitionRegistrar {@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Dog.class).getBeanDefinition();//实现对car bean的覆盖，当前car的对象是dogregistry.registerBeanDefinition("car",beanDefinition);}
}

@Import({MyImportBeanDefinition.class})
public class SpConfig5 {@Beanpublic Car car(){return new Car();}
}

9、导入实现了BeanDefinitionRegistryPostProcessor接口的类，通过BeanDefinition的注册器注册实名bean实现对容器中bean的最终定义

public class Car {
}

public class Car2 {private String name;@Overridepublic String toString() {return "Car2{" +"name='" + name + '\'' +'}';}
}

public class MyImportSelector implements ImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata importingClassMetadata) {//各种条件判断boolean b = importingClassMetadata.hasAnnotation("org.springframework.context.annotation.Import");System.out.println("flag:"+b);if (b){return new String[]{"com.melax.ailatest.bean.car"};}else {return new String[0];}}
}

@Import({MyPostProcessor.class})
public class SpConfig6 {@Beanpublic Car car(){return new Car();}
}