Question

这是我的代码

LoginController.java

package mvc.demo.control;

    import java.io.IOException;
    import java.io.PrintWriter;
    import javax.servlet.RequestDispatcher;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;

    import mvc.demo.model.Authenticate;


    public class LoginController extends HttpServlet {
        private static final long SerialVersionUID=1L;

        public LoginController()
        {
            super();
        }

        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp)
                throws ServletException, IOException {
            String s1=req.getParameter("username");
            String s2=req.getParameter("password");
            RequestDispatcher rd=null;
            Authenticate au=new Authenticate();
            String result=au.authorise(s1, s2);
            if(result.equals("success"))
            {
                rd=req.getRequestDispatcher("/success.jsp");    
            }
            else
            {
               //This is the point where i try to print error message on jsp.
                PrintWriter out = resp.getWriter(  );
                out.print("Sorry UserName or Password Error!");
                rd=req.getRequestDispatcher("/login.jsp");  
                rd.include(req, resp);  
            }
            rd.forward(req, resp);
        }   
    }

的login.jsp

    <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <title>Login Page</title>
    </head>
    <body>
        <form method="post" action="LoginController" >  
        UserName:   <input type="text" name="username"><BR><BR>
        PassWord:   <input type="password" name="password"><BR><BR>
                    <input type="submit" />   
        </form>
    </body>
    </html>

请检查loginController类的else块我试图在我的jsp文件上打印错误消息，目前“out.print”方法无法反映在我的login.jsp文件中。请帮我解决这个问题，提前谢谢。

Answer 1

您可以在请求属性中设置错误消息，并可以在JSP

中获取它

String errorMsg = "UserName or Password is invalid !";
req.setAttribute("errorMsg", errorMsg);
req.getRequestDispatcher("/login.jsp").forward(req, res);

现在在JSP上

<h2>${errorMsg}</h2>  // Print wherever you need it

Answer 2

 return array(
     'controllers' => array(
         'invokables' => array(
             'Album\Controller\Album' => 'Album\Controller\AlbumController',
             'Album\Controller\Albums' => 'Album\Controller\AlbumsController', // added second controller
         ),
     ),

     // The following section is new and should be added to your file
     'router' => array(
         'routes' => array(
             'album' => array(
                 'type'    => 'segment',
                 'options' => array(
                     'route'    => '/album[/:action][/:id]',
                     'constraints' => array(
                         'action' => '[a-zA-Z][a-zA-Z0-9_-]*',
                         'id'     => '[0-9]+',
                     ),
                     'defaults' => array(
                         'controller' => 'Album\Controller\Album',
                         'action'     => 'add',
                     ),
                 ),
             ),

             // add route to new controller
             'albums' => array(
                 'type'    => 'segment',
                 'options' => array(
                     'route'    => '/albums[/:action]',
                     'constraints' => array(
                         'action' => '[a-zA-Z][a-zA-Z0-9_-]*',
                     ),
                     'defaults' => array(
                         'controller' => 'Album\Controller\Albums',
                         'action'     => 'index',
                     ),
                 ),
             ),
         ),
     ),

 // ...

Answer 3

我在代码中看不到out.close（）。您必须最后关闭PrintWriter对象。

Answer 4

如果您想在Jsp中打印错误消息并首先在请求中设置错误消息

        req.setAttribute("msg","error msg configure here");

现在你可以使用EL Expression在jsp中获得相同的效果。

   ${msg}

或者您可以使用脚本语言来获取它。

 <%Object obj=request.getAttribute("msg");%>

将Obj转换为String并使用此

进行打印

             <%=str%>

注意： - 建议使用El表达式。

Out.Print方法不起作用？

4 个答案: