Spring

学习 Spring，跟着二哥简单写个 IoC 容器。 @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) @interface MyAutowired { } @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @interface MyComponent { } public class SimpleIoC { Map<Class<?>, Object> beans = new HashMap<>(); //扫描 public void scan(String packageName) { List<Class<?>> classes = getClassesInPackage(packageName); for (Class<?> clazz : classes) { if (clazz.isAnnotationPresent(MyComponent.class)) { registerBean(clazz); } } di(); } //获取包下的类，简化实现 private List<Class<?>> getClassesInPackage(String packageName) { // 实际实现需要扫描classpath，这里简化处理. return Arrays.asList(UserDao.class, UserService.class); } //注册bean private void registerBean (Class<?> clazz) { try { Object instance = clazz.getDeclaredConstructor().newInstance(); beans.put(clazz, instance); } catch (Exception e) { throw new RuntimeException("创建bean失败"); } } //获取bean @SuppressWarnings("unchecked") public <T> T getBean(Class<T> clazz) { return (T)beans.get(clazz); } //依赖注入 private void di() { for (Object bean : beans.values()) { Field[] fields = bean.getClass().getDeclaredFields(); for (Field field : fields) { if (field.isAnnotationPresent(MyAutowired.class)) { field.setAccessible(true); Object dependency = getBean(field.getType()); try { field.set(bean, dependency); } catch (Exception e) { throw new RuntimeException("依赖注入失败"); } } } } } } //DAO层 @MyComponent class UserDao { public void save(String user) { System.out.println("保存用户: " + user); } } // Service层 @MyComponent class UserService { @MyAutowired private UserDao userDao; public void createUser(String name) { userDao.save(name); System.out.println("用户创建完成"); } } class Test { public static void main(String[] args) { SimpleIoC ioc = new SimpleIoC(); ioc.scan("package"); UserService bean = ioc.getBean(UserService.class); bean.createUser("dong"); } } 参考链接： ...