Spring自动织入的理解

理解Bean注入

1.1 定义服务Service

public class UserService {

}

1.2 在服务中引入Service

public class UserController {

    private UserService userService;

    public UserService getUserService() {
        return userService;
    }

    public void setUserService(UserService userService) {
        this.userService = userService;
    }
}

1.3 编写注入方法

public class TestSetInjection {
    public static void main(String[] args) throws Exception{
        UserController userController = new UserController();
        UserService userService = new UserService();
        System.out.println(userService);
        // 将userService注入到userController中

        // 1. 获取class对象
        Class<? extends UserController> clazz = userController.getClass();

        // 2. 获取属性
        Field userServiceField = clazz.getDeclaredField("userService");
        // 也可以不设置可见性
        userServiceField.setAccessible(true);

        // 3. 获取对应的set方法
        String name  = userServiceField.getName();
        String methodName = "set" + name.substring(0,1).toUpperCase() + name.substring(1,name.length());
        Method method = clazz.getMethod(methodName, UserService.class);

        // 4. 调用setUserService方法
        method.invoke(userController, userService);
        System.out.println(userController.getUserService());
    }
}

理解Autowired

1.1 编写自定义注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Inherited
@Documented
public @interface Autowired {
}

1.2 编写Service

public class UserService {
}

1.3 编写Controller自动织入Service

public class UserController {
    @Autowired
    private UserService userService;

    public UserService getUserService() {
        return userService;
    }
}

1.4 编写工厂方法注入bean

public class TestAutowired {

    public static void main(String[] args){
        UserController userController = new UserController();

        // 获取clazz对象
        Class<? extends UserController> clazz = userController.getClass();
        Stream.of(clazz.getDeclaredFields()).forEach(
                field -> {
                    // 判断属性是否有注解
                    Autowired annotation = field.getAnnotation(Autowired.class);
                    if(annotation != null){
                        field.setAccessible(true);
                        // 获取当前属性的类型，有了类型可以创建具体的对象
                        Class<?> type = field.getType();
                        // 创建对象
                        try {
                            // 类似于demo1中的new Service
                            Object instance = type.newInstance();
                            // 给属性赋值
                            field.set(userController, instance);
                        } catch (InstantiationException e) {
                            e.printStackTrace();
                        } catch (IllegalAccessException e) {
                            e.printStackTrace();
                        }
                    }
                }
        );
        System.out.println(userController.getUserService());
    }
}

源码参考

SpringCore