Java Servlet 前端控制器

Question

我对这种模式Design Patterns web based applications 有点困惑。 我正在尝试开发简单的登录示例。我有登录成功的表单和 home.jsp 的 login.jsp。

在 ActionFactory 类中，我登录了地图和返回主页的 LoginAction。我的 ActionController 类与上面的链接一样，并使用 /pages/* 映射。 我应该使用什么 url 来调用 loginAction？ 如果我使用 /login 前端控制器不匹配它，如果我使用 /pages/login 它匹配它但是当“home”来到 FrontController 操作时为空。我也应该对 home.jsp 采取行动吗？在那种情况下，如何实现重定向？

动作工厂

public class ActionFactory {

    private static ActionFactory instance;

    public ActionFactory() {
        actions = new HashMap<>();
        actions.put("login", new LoginAction());
    }

    public static ActionFactory getInstance() {
        if (instance == null) {
            return new ActionFactory();
        } else {
            return instance;
        }
    }

    Map<String, Action> actions;

    public Action getAction(HttpServletRequest request) {
        return actions.get(request.getPathInfo().substring(1));
    }
}

Servlet

@WebServlet(name = "ActionController", urlPatterns = {"/pages/*"})
public class ActionController extends HttpServlet {

/**
 * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
 * methods.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    try {
        Action action = ActionFactory.getInstance().getAction(request);
        String view = action.execute(request, response);
        if (view.equals(request.getPathInfo().substring(1))) {
            request.getRequestDispatcher("/" + view + ".jsp").forward(request, response);
        } else {
            response.sendRedirect(view); // We'd like to fire redirect in case of a view change as result of the action (PRG pattern).
        }
    } catch (Exception e) {
        throw new ServletException("Executing action failed.", e);
    }
}

// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
 * Handles the HTTP <code>GET</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Handles the HTTP <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Returns a short description of the servlet.
 *
 * @return a String containing servlet description
 */
@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>

}

登录操作

public class LoginAction implements Action{

    @Override
    public String execute(HttpServletRequest request, HttpServletResponse response) throws Exception {
        return "home";
    }
}

Answer 1

我想这篇文章可以帮到你。

How come request.getPathInfo() in service method returns null?

您想使用 HttpServletRequest#getServletPath() 并且网址是 /pages/login

简单修复：调用页面“login.jsp”，Action的execute方法返回字符串“login”，测试的url又是“/pages/login”