Struts2 自定義 MVC 框架實現原理與代碼

架構設計

模仿 Struts2 核心流程：配置解析 → Action 映射管理 → 反射實例化 → 請求分發 → 結果視圖跳轉。

1. 配置文件 framework.xml

<framework>
    <actions>
        <action name="loginAction" class="cn.hq.Action.LoginAction">
            <result name="success">success.jsp</result>
            <result name="login">index.jsp</result>
        </action>
    </actions>
</framework>

2. 核心接口與類

// Action 接口
public interface Action {
    String execute(HttpServletRequest req, HttpServletResponse resp) throws Exception;
    String SUCCESS = "success";
    String LOGIN = "login";
}

// ActionMapping 封裝 action 節點
public class ActionMapping {
    private String name, className;
    private Map<String, String> results = new HashMap<>();
    // getter/setter/addResult
}

// ActionMappingManager 解析 XML 管理映射 (dom4j)
public class ActionMappingManager {
    private Map<String, ActionMapping> mappings = new HashMap<>;
    public ActionMappingManager(String[] configFiles) { ... 初始化解析 ... }
    public ActionMapping getMapping(String name) { return mappings.get(name); }
}

// ActionManager 反射獲取 Action 實例
public class ActionManager {
    public static Action getAction(String className) {
        Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
        return (Action) clazz.newInstance();
    }
}

3. 核心 Servlet 分發器

public class MyServlet extends HttpServlet {
    private ActionMappingManager manager;

    @Override public void init(ServletConfig config) {
        String cfg = config.getInitParameter("config");
        String[] files = cfg != null ? cfg.split(",") : new String[]{"Framework.xml"};
        manager = new ActionMappingManager(files);
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        String path = req.getRequestURI().substring(req.getContextPath().length());
        String actionName = path.substring(1, path.lastIndexOf('.')); // /loginAction.do -> loginAction

        ActionMapping mapping = manager.getMapping(actionName);
        Action action = ActionManager.getAction(mapping.getClassName());
        String result = action.execute(req, resp);
        String view = mapping.getResults().get(result);
        resp.sendRedirect(view);
    }
}

4. web.xml 配置

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>cn.hq.servlet.MyServlet</servlet-class>
    <init-param>
        <param-name>config</param-name>
        <param-value>Framework.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>*.do</url-pattern>
</servlet-mapping>

5. 測試 Action

public class LoginAction implements Action {
    public String execute(HttpServletRequest req, HttpServletResponse resp) {
        if ("1".equals(req.getParameter("name")) && "1".equals(req.getParameter("pwd"))) {
            return SUCCESS;
        }
        return LOGIN;
    }
}

設計亮點

• 配置與代碼分離，擴展性強
• dom4j 解析 XML，反射實例化，符合 MVC 解耦思想
• 結果視圖映射靈活配置，支持重定向/轉發擴展