@Component,@Bean同时作用同一个类

测试程序

@Configuration
@ComponentScan("com.test")
public class UserConfig {
    @Value("${key1}")
    String userName;

    @Bean
    public UserManager userManager(){ 
        UserManager userManager = new UserManager(userName);
        return userManager;
    }
}

@Component
public class UserManager {
    String userName;

    public UserManager() {
        System.out.println("constructor UserManager()");
    }

    public UserManager(String userName) {
        this.userName = userName;
        System.out.println("constructor UserManager(String userName)");
    }
}

@Component
public class UserPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {

    @Override
    protected void loadProperties(Properties props) throws IOException {
        super.loadProperties(props);
        props.put("key1", "value1");
    }
}

测试代码

public static void main(String[] args) {
    AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(UserConfig.class);
    UserManager userManager = ac.getBean(UserManager.class);
    System.out.println(userManager);
}

结论

默认 @Configuration + @Bean 会覆盖 @Component

源码流程

在执行ConfigurationClassPostProcessor的postProcessBeanFactory方法时，BeanDefinition会注册两次

• 第一次：ConfigurationClassPostProcessor内部的@ComponentScan扫描bean完成注册
• 第二次：ConfigurationClassPostProcessor全注解类内部的@Bean方法解析去注册bean,而这会对第一次的注册进行覆盖