【spring】bean的加载的方式

1.xml方式声明bean

package com.learning;

import com.learning.bean.Dog;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
public class Application {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        Object cat = applicationContext.getBean("cat");
        System.out.println(cat);
        Dog dog = applicationContext.getBean(Dog.class);
        System.out.println(dog);

        String[] beanDefinitionNames = applicationContext.getBeanDefinitionNames();
        for (String bean: beanDefinitionNames) {
            System.out.println(bean);
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="cat" class="com.learning.bean.Cat"/>
    <bean class="com.learning.bean.Dog"/>
</beans>

2.xml+注解方式声明bean

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd">
    <context:component-scan base-package="com.learning"/>
</beans>

package com.learning.bean;

import com.alibaba.druid.pool.DruidDataSource;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

/**
 * @Author wangyouhui
 * @Description
 **/
@Component
public class DbConfig {
    @Bean
    public DruidDataSource getDataSource(){
        DruidDataSource dataSource = new DruidDataSource();
        return dataSource;
    }
}

3.注解方式声明配置类

package com.learning.bean;

import com.alibaba.druid.pool.DruidDataSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.Component;

/**
 * @Author wangyouhui
 * @Description
 **/
@Component
@ComponentScan("com.learning")
public class DbConfig {
    @Bean
    public DruidDataSource getDataSource(){
        DruidDataSource dataSource = new DruidDataSource();
        return dataSource;
    }
}

4.实现FactoryBean接口

package com.learning.bean;

import org.springframework.beans.factory.FactoryBean;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
public class DogFactoryBean implements FactoryBean<Dog> {
    @Override
    public Dog getObject() throws Exception {
        return new Dog();
    }

    @Override
    public Class<?> getObjectType() {
        return Dog.class;
    }

    @Override
    public boolean isSingleton() {
        return false;
    }
}

package com.learning;

import com.learning.bean.DogFactoryBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
@ComponentScan("com.learning")
public class DogConfig {
    @Bean
    public DogFactoryBean dog(){
        return new DogFactoryBean();
    }
}

5.使用@Import注解导入配置类

package com.learning;

import com.learning.bean.DbConfig;
import org.springframework.context.annotation.Import;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
@Import(DbConfig.class)
public class SpringConfig {
}

6.使用上下文对象在容器初始化完毕后注入bean

package com.learning;

import com.learning.bean.Cat;
import com.learning.bean.Dog;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
public class Application3 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);
        applicationContext.register(Cat.class);

        String[] beanDefinitionNames = applicationContext.getBeanDefinitionNames();
        for (String bean: beanDefinitionNames) {
            System.out.println(bean);
        }
    }
}

7.导入实现了ImportSelector接口的类，实现对导入源的编程式处理

package com.learning.selector;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
public class MyImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        boolean flag = annotationMetadata.hasAnnotation("org.springframework.context.annotation.Import");
        if(flag){
            return new String[]{"com.learning.bean.Cat"};
        }
        return new String[]{"com.learning.bean.Dog"};
    }
}

package com.learning;

import com.learning.selector.MyImportSelector;
import org.springframework.context.annotation.Import;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
@Import(MyImportSelector.class)
public class SpringConfig {
}

8.导入实现了ImportBeanDefinitionRegistrar接口的类

1.通过BeanDefinition的注册器注册实名Bean，实现对容器中bean的裁定
2.可以对现有bean的覆盖，达到不修改源代码的情况下更换实现的效果

package com.learning.registry;

import com.learning.bean.Dog;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
public class MyRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry){
        // 1.使用元数据去做判定

        BeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Dog.class).getBeanDefinition();
        registry.registerBeanDefinition("bean1",beanDefinition);
    }
}

package com.learning;

import com.learning.registry.MyRegistrar;
import org.springframework.context.annotation.Import;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
@Import(MyRegistrar.class)
public class SpringConfig {
}

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的最终裁定

package com.learning.processor;

import com.learning.bean.Dog;
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.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;

/**
 * @Author wangyouhui
 * @Description TODO
 **/
public class MyPostProcessor implements BeanDefinitionRegistryPostProcessor {
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
        BeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Dog.class).getBeanDefinition();
        beanDefinitionRegistry.registerBeanDefinition("dog", beanDefinition);
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {

    }
}