笔记

Spring IOC

Inverse of Control：控制反转

DI：Dependancy Injections：依赖注入

没有IOC的时候，各种依赖需要逐个按顺序创建。

有了IOC的之后，只要告诉那个依赖那个就可以了，容器会自动装配好依赖

手写一个IOC容器

public class MyIoCContainer {

    // 实现一个简单的IoC容器，使得：

    // 1. 从beans.properties里加载bean定义

    // 2. 自动扫描bean中的@Autowired注解并完成依赖注入

    public static void main(String[] args) {

        MyIoCContainer container = new MyIoCContainer();

        container.start();

        OrderService orderService = (OrderService) container.getBean("orderService");

        orderService.createOrder();

    }

    private static Map<String, Object> beans = new HashMap<>();

    // 启动该容器

    public void start() {

        Properties properties = new Properties();

        try {

            properties.load(MyIoCContainer.class.getResourceAsStream("/beans.properties"));

            properties.forEach((beanName, beanClass) -> {

                try {

                    Class<?> klass = Class.forName(String.valueOf(beanClass));

                    Object beanInstance = klass.getConstructor().newInstance();

                    beans.put(String.valueOf(beanName), beanInstance);

                } catch (Exception e) {

                    throw new RuntimeException(e);

                }

            });

            beans.forEach((beanName, beanInstance) -> dependencyInject(beanName, beanInstance, beans));

        } catch (IOException e) {

            throw new RuntimeException(e);

        }

    }

    // 从容器中获取一个bean

    public Object getBean(String beanName) {

        return beans.get(beanName);

    }

    private static void dependencyInject(String beanName, Object beanInstance, Map<String, Object> beans) {

        List<Field> fieldsToBeAutowired = Stream.of(beanInstance.getClass().getDeclaredFields())

                .filter(field -> field.getAnnotation(Autowired.class) != null)

                .collect(Collectors.toList());

        fieldsToBeAutowired.forEach(field -> {

            try {

                String fieldName = field.getName();

                Object dependencyBeanInstance = beans.get(fieldName);

                field.setAccessible(true);    //打破封装性，访问私有成员方法或变量

                field.set(beanInstance, dependencyBeanInstance);

            } catch (IllegalAccessException e) {

                throw new RuntimeException(e);

            }

        });

    }

}

巴特西

今日份学习： Spring - 事实标准

笔记

Spring IOC

手写一个IOC容器

最新文章

热门文章