UserController{UserService userService = new UserService();userService.insert(user);
}UserController{@AutowwiredUserService userService;userService.insert(user);
}

@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
public @interface MyService {}@Target({ TYPE, FIELD, METHOD })
@Retention(RUNTIME)
public @interface MyAutowired {}

@MyService
public class OrderService {public void add() {System.out.println("Order....add()");}
}@MyService
public class UserService {@MyAutowiredprivate OrderService orderService;public void add() {orderService.add();System.out.println("User....add()");}
}

/*** SpringIOC容器实现过程*/
public class MyClassPathXmlApplicationContext {// 1. 指定扫描包的范围private String packageName ;// Spring的bean容器 (容器启动时初始化所有bean,默认单例)  key:beanName(默认类名小写)  value:bean对象private ConcurrentHashMap<String, Object> beans;public MyClassPathXmlApplicationContext(String packageName) throws Exception {// 类加载时初始化这些参数this.packageName = packageName;this.beans = new ConcurrentHashMap<String, Object>();initBeans();// 初始化所有类initEntryField();// 初始化所有类的属性
    }/*** 初始化bean(IOC控制反转)*/public void initBeans() throws Exception {// 2. 通过java反射扫描指定包下面所有类的class地址List<Class<?>> classes = ClassUtil.getClasses(packageName);ConcurrentHashMap<String, Object> classExistAnnotation = this.findClassExistAnnotation(classes);if(classExistAnnotation == null || classExistAnnotation.isEmpty()) throw new Exception("cannot find bean");}/*** 判断类上面是否存在bean的注解*/private ConcurrentHashMap<String, Object> findClassExistAnnotation(List<Class<?>> classes) throws InstantiationException, IllegalAccessException {for(Class<?> classInfo : classes) {// 3. 获取指定路径中有ioc注解的类MyService annotation = classInfo.getAnnotation(MyService.class);if(annotation!=null) {String className = classInfo.getSimpleName();// 获取类名称// 4. 将类名首字母小写,获取bean名称。String beanaName = StringUtil.toLowerCaseFirstOne(className);// 5. 反射初始化对象Object object = classInfo.newInstance();// 6. 将bean对象存入spring容器中
                beans.put(beanaName, object);}}return beans;// 对象初始化完成
    }    /*** 初始化属性*/private void initEntryField() throws Exception {// 7. 遍历spring容器中所有的bean对象for (Entry<String, Object> entry : beans.entrySet()) {Object bean = entry.getValue();this.attriAssign(bean);}}/*** 依赖注入实现原理(DI依赖注入)*/public void attriAssign(Object object) throws Exception {Class<? extends Object> classInfo = object.getClass();// 8. 使用反射机制,获取当前类的所有属性值Field[] fields = classInfo.getDeclaredFields();for(Field field : fields) {// 9. 获取有@MyAutowired注解的属性MyAutowired myAutowired = field.getAnnotation(MyAutowired.class);if(myAutowired != null) {// 10. 获取属性名称String beanName = field.getName();// 11. 默认使用属性名称,查找bean容器对象Object bean = this.getBean(beanName);if(bean != null) {field.setAccessible(true);// 允许访问私有属性// 12. 将得到的bean对象赋值给当前对象的属性上。(bean名称=属性名称)
                    field.set(object, bean);}}}}/*** 通过bean名称去spring容器里面获取bean对象*/public Object getBean(String beanName) throws Exception {if(StringUtils.isEmpty(beanName)) throw new Exception("beans.factory.BeanCreationException");Object object = beans.get(beanName);return object;}/*** 测试*/public static void main(String[] args) throws Exception {MyClassPathXmlApplicationContext applicationContext = new MyClassPathXmlApplicationContext("com.wulei.service");UserService userService = (UserService)applicationContext.getBean("userService");userService.add();}
}