在SpringBoot项目中，我可以说出7种注册bean的方式

Java进阶之路

发布于 2022-11-18 15:21:36

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发布于 2022-11-18 15:21:36

文章被收录于专栏：分布式与微服务

前言

Spring和SpringBoot是当前最火的Java开发框架，很多时候我们都会将对象注册到Spring的容器中，将对象交给Spring来管理，那么今天我们就来盘点一下将Bean注册到Spring容器的7种方式。

一：xml配置 + @ImportResource

@Data
public class XmlTestBean {

    private Integer age;

    private String name;
    
}

① 在resource目录下创建Spring的xml配置文件

<?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 name="xmlTestBean" class="com.example.demo.XmlTestBean">
        <property name="age" value="18"/>
        <property name="name" value="xmlBean"/>
    </bean></beans>复制代码

② 利用@ImportResource注解导入xml配置文件

@SpringBootApplication
@ImportResource("classpath:XmlTestBean.xml")
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(DemoApplication.class, args);

        XmlTestBean bean = run.getBean(XmlTestBean.class);

        System.out.println(bean);
    }

}

输出结果：

二：@Component + @ComponentScan

① 在需要注册的类上加@Component注解，并且通过@ComponentScan对其进行扫描。

@Component
@Data
public class ComponentTestBean {

    private Integer age = 18;

    private String name = "componentTestBean";
    
}

② 通过@ComponentScan注解扫描有@Component注解的类

@SpringBootApplication(scanBasePackages = "com.example.demo")
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(DemoApplication.class, args);

        ComponentTestBean bean = run.getBean(ComponentTestBean.class);

        System.out.println(bean);
    }
}

输出结果：

注：@Service，@Controller，@Repository，@Configuration注解都是@Component注解的复合注解，都归为一类吧。

三: @Configuration + @Bean + @ComponentScan

@Data
public class ConfigurationTestBean {

    private Integer age;

    private String name;
}

① 通过@Configuration和@Bean注解定义bean的信息


@Configuration
public class TestBeanConfiguration {

    @Bean
    public ConfigurationTestBean configurationTestBean(){
        ConfigurationTestBean configurationTestBean = new ConfigurationTestBean();
        configurationTestBean.setAge(18);
        configurationTestBean.setName("configurationTestBean");
        return configurationTestBean;
    }
}

②：利用@ComponentScan注解扫描@Configuration注解

@SpringBootApplication(scanBasePackages = "com.example.demo")
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(DemoApplication.class, args);

        ConfigurationTestBean bean = run.getBean(ConfigurationTestBean.class);

        System.out.println(bean);
    }

}

输出结果：

四：实现FactoryBean接口

@Data
public class TestFactoryBean {

    private Integer age;

    private String name;
}

① 实现FactoryBean接口

重写getObject()方法，在getObject()方法中定义bean的信息。

@Component
public class FactoryBeanTest implements FactoryBean<TestFactoryBean> {
    @Override
    public TestFactoryBean getObject() throws Exception {
        TestFactoryBean testFactoryBean = new TestFactoryBean();
        testFactoryBean.setAge(18);
        testFactoryBean.setName("testFactoryBean");
        return testFactoryBean;
    }

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

② 利用@ComponentScan注解扫描FactoryBean实现类的@Component注解

@SpringBootApplication(scanBasePackages = "com.example.demo")
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(DemoApplication.class, args);

        TestFactoryBean bean = run.getBean(TestFactoryBean.class);

        System.out.println(bean);
    }

}

输出结果：

五：实现BeanDefinitionRegistryPostProcessor接口

@Data
public class RegisterTestBean {

    private Integer age;

    private String name;
}

①：实现BeanDefinitionRegistryPostProcessor接口

实现BeanDefinitionRegistryPostProcessor接口，并且重写postProcessBeanDefinitionRegistry方法，利用BeanDefinitionBuilder构建BeanDefinition，然后利用BeanDefinitionRegistry将bean进行注册。

@Component
public class RegisterBeanTest implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        BeanDefinitionBuilder beanDefinitionBuilder = 
                BeanDefinitionBuilder.genericBeanDefinition(RegisterTestBean.class);

        beanDefinitionBuilder.addPropertyValue("age",18);
        beanDefinitionBuilder.addPropertyValue("name","registerTestBean");

        AbstractBeanDefinition beanDefinition = beanDefinitionBuilder.getBeanDefinition();
        
        registry.registerBeanDefinition("registerTestBean",beanDefinition);

    }

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

    }
}

注：也可以在postProcessBeanFactory方法中实现相关的逻辑，因为在这里ConfigurableListableBeanFactory其实也是BeanDefinitionRegistry类型，可以进行强转。

②利用@ComponentScan注解扫描BeanDefinitionRegistryPostProcessor实现类的@Component注解

@SpringBootApplication(scanBasePackages = "com.example.demo")
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(DemoApplication.class, args);

        RegisterTestBean bean = run.getBean(RegisterTestBean.class);

        System.out.println(bean);
    }

}

输出结果：

六：实现BeanFactoryPostProcessor接口

① 实现BeanFactoryPostProcessor接口，利用BeanDefinitionBuilder构建bean的信息，然后通过BeanDefinitionRegistry将bean注册到Spring容器中。

@Data
public class BeanFactoryProcessorTestBean {

    private Integer age;

    private String name;
}

@Component
public class TestBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
        
        if (configurableListableBeanFactory instanceof BeanDefinitionRegistry){
            BeanDefinitionBuilder beanDefinitionBuilder =
                    BeanDefinitionBuilder.genericBeanDefinition(BeanFactoryProcessorTestBean.class);

            beanDefinitionBuilder.addPropertyValue("age",18);
            beanDefinitionBuilder.addPropertyValue("name","BeanFactoryProcessorTestBean");

            AbstractBeanDefinition beanDefinition = beanDefinitionBuilder.getBeanDefinition();
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry)configurableListableBeanFactory;
            registry.registerBeanDefinition("beanFactoryProcessorTestBean",beanDefinition);
        }
    }
}

② 利用@ComponentScan注解扫描BeanFactoryPostProcessor实现类的@Component注解

@SpringBootApplication(scanBasePackages = "com.example.demo")
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(DemoApplication.class, args);

        BeanFactoryProcessorTestBean bean = run.getBean(BeanFactoryProcessorTestBean.class);

        System.out.println(bean);
    }
}

输出结果：