實戰總結｜複雜系統設計原則與案例

public interface HandlerMapping {
   HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    // 抽象方法，交由具體的子類實現
    Object handler = getHandlerInternal(request);
    if (handler == null) {
        handler = getDefaultHandler();
    }
    if (handler == null) {
        return null;
    }
    
    // 省略部分代碼
    HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

    // 省略部分代碼
    return executionChain;
}
在MyBatis框架中，Executor定義了增刪改查等方法，具體實現有如單條命令執行、批量命令執行等，模板方法定義在Ba

@RestController
public class UserController {

    @RequestMapping(value = "/acquire", method = RequestMethod.GET)
    public User getUser(@RequestParam("name") String name, @RequestParam("age") Integer age) {

        return null;
    }
}

public interface BeanPostProcessor {
    // 初始化前的操作
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
  
    // 初始化後的操作
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

/**
 * 事件分發器
 *
 * @author fulai.gfl
 */
public class EventDispatcher {

    /**
     * 事件列表
     */
    private static List<Event> events = new ArrayList<>();

    /**
     * 事件處理器列表
     */
    private static List<Handler> handlers = new ArrayList<>();

    /**
     * 添加事件
     *
     * @param event
     */
    public static void addEvent(Event event) {
        events.add(event);
    }

    /**
     * 添加事件處理器
     *
     * @param handler
     */
    public static void addHandler(Handler handler) {
        handlers.add(handler);
    }

    /**
     * 觸發事件
     *
     * @param event
     * @return
     * @throws Exception
     */
    public Object fire(Event event) throws Exception {

        Handler handler = getHandler(event);
        if(Objects.isNull(handler)){
            throw new Exception("沒有找到指定的handler, event_name =" + event.getEventName());
        }

        return handler.handle(event);
    }

    /**
     * 根據事件找到對應的Handler
     *
     * @param event
     * @return
     * @throws Exception
     */
    private Handler getHandler(Event event) throws Exception {

        Handler handler = null;
        for (Handler h : handlers) {

            Type[] argumentsTypes = ((ParameterizedTypeImpl)h.getClass().getGenericInterfaces()[0])
                .getActualTypeArguments();

            if (Class.forName(((Class)argumentsTypes[0]).getName()).equals(event.getClass())) {
                handler = h;
            }

        }

        return handler;
    }
}