Spring 擴充 MultiActionController 實作自動 URL 映射（下）

目標

實作 MultiMethodControllerUrlHandlerMapping，自動掃描 Spring 容器中所有 MultiMethodController 型別的 Bean，讀取其 urlMethodMappings 屬性，建立「URL → Controller」對應表，免除手工在 SimpleUrlHandlerMapping 逐一配置。

核心實作

public class MultiMethodControllerUrlHandlerMapping
    extends AbstractUrlHandlerMapping {

    private Map<String, Object> urlMap = new HashMap<>();

    @Override
    protected void initApplicationContext() throws BeansException {
        initialUrlMap();
    }

    private void initialUrlMap() throws BeansException {
        // 1. 取得容器中所有 MultiMethodController 及其子類 Bean
        Map<String, MultiMethodController> matchingBeans =
            BeanFactoryUtils.beansOfTypeIncludingAncestors(
                getWebApplicationContext(),
                MultiMethodController.class, true, false);

        if (!matchingBeans.isEmpty()) {
            for (MultiMethodController controller : matchingBeans.values()) {
                Properties urlProps = controller.getUrlMethodMappings();
                for (String url : urlProps.stringPropertyNames()) {
                    urlMap.put(url, controller);  // URL → Controller 實例
                }
            }
        }
    }

    @Override
    protected Object getHandlerInternal(HttpServletRequest request)
        throws Exception {
        String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
        Object handler = urlMap.get(lookupPath);
        if (handler != null) {
            return handler;
        }
        return super.getHandlerInternal(request); // fallback
    }
}

關鍵點解析

1. 繼承 AbstractUrlHandlerMapping：自動擁有 WebApplicationContext 存取能力。
2. BeanFactoryUtils.beansOfTypeIncludingAncestors()：遞迴搜尋父容器，確保跨模組 Controller 皆被掃描。
3. MultiMethodController.getUrlMethodMappings()：約定 Controller 需暴露此屬性（Properties 型別），Key 為 URL，Value 為方法名。
4. 覆寫 getHandlerInternal()：依請求路徑直接從 urlMap 查找 Controller，效能 O(1)。

Spring 配置啟用

<bean class="com.yourpkg.MultiMethodControllerUrlHandlerMapping">
  <property name="order" value="0"/> <!-- 優先順序最高 -->
</bean>

Controller 端寫法

public class SampleMultiMethodController extends MultiActionController
    implements MultiMethodController {

    private Properties urlMethodMappings = new Properties();
    // setter/getter 略

    public ModelAndView listUser(HttpServletRequest req, HttpServletResponse res) { ... }
    public ModelAndView editUser(HttpServletRequest req, HttpServletResponse res) { ... }
    public ModelAndView saveUser(HttpServletRequest req, HttpServletResponse res, UserDTO cmd) { ... }
    public ModelAndView deleteUser(HttpServletRequest req, HttpServletResponse res) { ... }
}

在 Bean 定義中設定 urlMethodMappings：

<bean id="sampleMultiMethodController"
  class="com.prs.application.ehld.sample.web.controller.SampleMultiMethodController">
  <property name="urlMethodMappings">
    <props>
      <prop key="/ehld.sample.getuserinfolist.do">listUser</prop>
      <prop key="/ehld.sample.edituserinfo.do">editUser</prop>
      <prop key="/ehld.sample.saveuserinfo.do">saveUser</prop>
      <prop key="/ehld.sample.deleteuserinfo.do">deleteUser</prop>
    </props>
  </property>
  <property name="sampleAction" ref="sampleAction"/>
</bean>

優缺點總結

結語

透過自訂 UrlHandlerMapping 掃描 Controller 內部映射屬性，可大幅簡化 Spring MVC 早期版本的配置複雜度。現代專案請直接使用註解式開發，但此機制對理解 Spring MVC 請求分派原理極具參考價值。