可以使用这种方式往Spring 容器中 注册 bean

@Configuration
public class BeanConfig implements InitializingBean {
    @Autowired
    DefaultListableBeanFactory defaultListableBeanFactory;

    @PostConstruct
    // 先
    public void init() {
        String a = new String("aaaaa");
        // 往这里看，核心api
        defaultListableBeanFactory.registerSingleton("myStringBean", a);
    }

    @Autowired
    private ApplicationContext applicationContext;


    @Override
    // 后
    public void afterPropertiesSet() throws Exception {
        Object myStringBean = applicationContext.getBean("myStringBean");
        System.out.println(myStringBean); // aaaaa
    }
}