手撕Spring底层系列之：IOC、AOP

// 反射实现Bean实例化简化代码
public class SimpleBeanFactory {
    private Map<String, Object> singletonObjects = new ConcurrentHashMap<>();

    public Object getBean(String beanName) throws Exception {
        Object bean = singletonObjects.get(beanName);
        if (bean != null) return bean;

        // 反射创建对象（简化版）
        Class<?> clazz = Class.forName(beanName);
        bean = clazz.getDeclaredConstructor().newInstance();
        singletonObjects.put(beanName, bean);
        return bean;
    }
}

public class DefaultSingletonBeanRegistry {
    // 一级缓存：完整Bean
    private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
    // 二级缓存：早期引用（未填充属性）
    private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);
    // 三级缓存：Bean工厂（可生成代理对象）
    private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
}

<bean id="userDao" class="org.xt.dao.impl.UserDaoImpl"></bean>

<bean id="userService" class="org.xt.service.impl.UserServiceImpl">
  <property name="name" value="123"></property>
  <property name="userDao" ref="userDao"></property>
</bean>

<bean id="userService" class="org.xt.service.impl.UserServiceImpl">
  <property name="name" value="123"></property>
  <property name="userDao" ref="userDao"></property>
</bean>

<bean id="userDao" class="org.xt.dao.impl.UserDaoImpl"></bean>

public interface UserService {
    void show1();
    void show2();
}

//目标对象
public class UserServiceImpl implements UserService {
    @Override
    public void show1() {
        System.out.println("show1...");
    }

    @Override
    public void show2() {
        System.out.println("show2...");
    }
}

//增强类，内部提供增强方法
public class MyAdvice {
    public void beforeAdvice(){
        System.out.println("前置的增强...");
    }
    public void afterAdvice(){
        System.out.println("后置的增强...");
    }
}


public class MockAopBeanPostProcessor implements BeanPostProcessor, ApplicationContextAware {

    ApplicationContext applicationContext;

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        //  目的：对UserServiceImpl中的show1和show2方法进行增强，增强方法存在MyAdvice中
        //  问题1：筛选UserServiceImpl或者service.impl包下的所有方法都可以进行增强 解决方案：添加判断
        //  问题2：MyAdvice怎么获取到 解决方法：从spring容器中获取
        if(bean.getClass().getPackage().getName().equals("org.xt.service.impl")){
            //生成当前Bean的Proxy对象
            Object beanProxy = Proxy.newProxyInstance(
                bean.getClass().getClassLoader(),
                bean.getClass().getInterfaces(),
                (proxy, method, args) -> {
                    //执行增强对象的Before方法
                    MyAdvice myAdvice = applicationContext.getBean(MyAdvice.class);
                    myAdvice.beforeAdvice();
                    //执行目标对象的目标方法
                    Object result = method.invoke(bean, args);
                    //执行增强对象的After方法
                    myAdvice.afterAdvice();
                    return result;
                });
            return beanProxy;
        }
        return bean;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

// DefaultAopProxyFactory选择代理方式
public AopProxy createAopProxy(AdvisedSupport config) {
    if (config.isOptimize() || config.isProxyTargetClass()) {
        return new CglibAopProxy(config); // 使用CGLIB
    }
    return new JdkDynamicAopProxy(config); // 使用JDK代理
}

// JDK代理调用流程
public Object invoke(Object proxy, Method method, Object[] args) {
    // 1. 获取目标对象
    Object target = getTarget();
    // 2. 获取拦截器链
    List<Object> chain = getInterceptorsAndDynamicInterceptionAdvice(method);
    // 3. 执行拦截器链
    return new ReflectiveMethodInvocation(target, method, args, chain).proceed();
}

// 分布式事务切面示例
@Aspect
public class GlobalTransactionAspect {
    @Around("@annotation(com.distributed.tx)")
    public Object handleTransaction(ProceedingJoinPoint joinPoint) {
        try {
            // 1. 创建全局事务ID
            String txId = UUID.randomUUID().toString();
            // 2. 通知参与者注册事务
            TransactionManager.register(txId);
            // 3. 执行目标方法
            Object result = joinPoint.proceed();
            // 4. 提交事务
            TransactionManager.commit(txId);
            return result;
        } catch (Throwable e) {
            // 5. 回滚事务
            TransactionManager.rollback(txId);
            throw new RuntimeException(e);
        }
    }
}