实现Spring autowired

太牛了！竟然真的有人能花700分钟把Spring+springboot源码给讲透彻了（真香） 首先，我们有这两个类

public class UserController { private UserService userService ; public UserService getUserService() { return userService; } public void setUserService(UserService userService) { this.userService = userService; } } public class UserService { }

UserController类调用了UserService类但没有对其初始化，在spring中我们是通过@Autowired将UserService类这个类放入容器当中的，现在我们想手动实现了下@Autowired对应的功能，怎么做？答案是通过反射

@Test public void test() throws NoSuchFieldException, IllegalAccessException { UserController userController = new UserController(); Class<? extends UserController> aClass = userController.getClass(); //getDeclaredFields()：获得某个类的所有声明的字段，即包括public、private和proteced，但是不包括父类的申明字段。 Field[] declaredFields = aClass.getDeclaredFields(); for (int i = 0; i < declaredFields.length; i++) { System.out.println("declaredFields = "+declaredFields[i].getName()); } System.out.println(); Field[] fields = aClass.getFields(); //getFields()：获得某个类的所有的公共（public）的字段，包括父类中的字段。 for (int i = 0; i < fields.length; i++) { System.out.println("fields = "+fields[i].getName()); } System.out.println("complete"); } /*输出内容 declaredFields = userService complete */ @Test public void test2() throws Exception { UserController userController = new UserController(); /*得到UserController的实例*/ Class<? extends UserController> aClass = userController.getClass(); /*得到UserService的实例*/ UserService userService = new UserService(); System.out.println("userService = " + userService); /*得到UserController的字段*/ Field Filed = aClass.getDeclaredField("userService"); Filed.setAccessible(true); //可以访问私有属性的值 /*得到字段名称*/ String name = Filed.getName(); System.out.println("name = " + name); /*处理字段名称*/ name = name.substring(0,1).toUpperCase() + name.substring(1,name.length()) ; System.out.println("name = " + name); /*拼接字段名称*/ String setMethodName = "set" + name ; System.out.println("setMethodName = " + setMethodName); /*得到拼接好的字段名称对应的方法*/ Method method = aClass.getMethod(setMethodName, UserService.class); /*调用method的invoke方法 传递之前创建的userService对象*/ method.invoke(userController , userService) ; System.out.println(userController.getUserService()); }

好了，现在我们可以开始定义我们自己的注解了

@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface Myautowired { } public class UserController { @Myautowired private UserService userService ; public UserService getUserService() { return userService; } public void setUserService(UserService userService) { this.userService = userService; } } @Test public void test(){ UserController userController = new UserController(); Class<? extends UserController> aClass = userController.getClass(); // UserService userService = new UserService(); /*获取所有的属性值*/ Stream.of(aClass.getDeclaredFields()).forEach( field -> { String name = field.getName(); Myautowired annotation = field.getAnnotation(Myautowired.class); if (annotation != null){ field.setAccessible(true); Class<?> type = field.getType(); //获取属性的类型 try { Object o = type.newInstance(); //new一个UserService的对象 field.set(userController,o); } catch (InstantiationException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } } } ); System.out.println(userController.getUserService()); }