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SpringBoot將Bean放入容器的五種方式

 更新時(shí)間：2024年02月20日 10:46:30   作者：宣晨光  
這篇文章給大家介紹了SpringBoot將Bean放入容器的五種方式,文中通過代碼示例給大家介紹的非常詳細(xì),對大家的學(xué)習(xí)或工作有一定的幫助,需要的朋友可以參考下

1、@Configuration + @Bean

@Configuration
public class MyConfiguration {
    @Bean
    public 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;
    }
    @Override
    public 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注解導(dǎo)入

@import注解源碼

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
 
    /**   * 用于導(dǎo)入一個(gè)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注解導(dǎo)入類

然后自動(dòng)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;
    }
 
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}
/*** 直接使用@Import導(dǎo)入person類，然后嘗試從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 {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{"com.springboot.pojo.Person"};
    }
}

3.3 @Import + ImportBeanDefinitionRegistrar

bean的定義(bean的元數(shù)據(jù))，也是需要放在IOC容器中進(jìn)行管理的，先有bean的元數(shù)據(jù)，

applicationContext再根據(jù)bean的元數(shù)據(jù)去創(chuàng)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 {
 
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        // 構(gòu)建一個(gè)beanDefinition, 關(guān)于beanDefinition我后續(xù)會(huì)介紹，可以簡單理解為bean的定義.
        AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Person.class).getBeanDefinition();
        // 將beanDefinition注冊到Ioc容器中.
        registry.registerBeanDefinition("person", beanDefinition);
    }
}

3.4 @Import + DeferredImportSelector

DeferredImportSelector 它是 ImportSelector 的子接口，所以實(shí)現(xiàn)的方法和第二種無異。

只是Spring的處理方式不同，它和Spring Boot中的自動(dòng)導(dǎo)入配置文件 延遲導(dǎo)入有關(guān)

@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 {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        // 也是直接將Person的全限定名放進(jìn)去
        return new String[]{Person.class.getName()};
    }
}

4、使用FactoryBean接口

FactoryBean, 后綴為bean，那么它其實(shí)就是一個(gè)bean,

BeanFactory，顧名思義 bean工廠，它是IOC容器的頂級接口

@Configuration
public class Demo1 {
    @Bean
    public 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出來Person進(jìn)行返回.     */
    @Override
    public Person getObject() throws Exception {
        return new Person();
    }
    /**     *  指定返回bean的類型.     */
    @Override
    public Class<?> getObjectType() {
        return Person.class;
    }
}

5、使用 BeanDefinitionRegistryPostProcessor

等beanDefinition加載完畢之后，對beanDefinition進(jìn)行后置處理，

可以在此進(jìn)行調(diào)整IOC容器中的beanDefinition，從而干擾到后面進(jìn)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 {
 
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Person.class).getBeanDefinition();
        registry.registerBeanDefinition("person", beanDefinition);
    }
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
 
    }
}

以上就是SpringBoot將Bean放入容器的五種方式的詳細(xì)內(nèi)容，更多關(guān)于SpringBoot Bean放入容器的資料請關(guān)注腳本之家其它相關(guān)文章！

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