Redirecting to the root URL in servlet

2019-08-01 02:49发布

站内问答 / Java
1743 1 4

Hi I did simple web application with servlet, to serve login and welcome page based on the session available. I had attached the code below,

whenever the user types the URL http://localhost:8888/, he must take to the dashboard servlet (as mention in the web.xml)

In the dashboard servlet, where session is checked

if the session is available, then I will serve welcome.html page, else I redirect to login servlet

In the login servlet,

GET method, if the user have the session I redirect to the dashboard servlet else I will the forward the welcome.html page

after user entry the information, it will post the information to the login servlet (i.e., POST)

POST method, I will get the username and password from the request, I will check value is admin and password

if it is true create a session and redirect the user to the dashboard servlet else I will redirect the user to the login servlet(GET Method)

web application should need to have only these 2 URL,

(1) http://localhost:8888/ (2) http://localhost:8888/login

user should not aware of the type of page I am serving to them(html or jsp) but I need to serve HTML page only(this my requirement)

when I start the app engine, At first the request send to dashboard then it is redirected to the login servlet but then its making loop for the dashboard once again,

I used System.out.println() to track the control my output is 

The admin console is running at http://localhost:8888/_ah/admin
Jul 25, 2017 11:12:55 AM com.google.appengine.tools.development.DevAppServerImpl doStart
INFO: Dev App Server is now running
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,
login servlet get method
request no session
-->dashboard servlet
get method
no session,

QUESTION:

How can solve this problem?

If I change url pattern in web.xml as <url-pattern>/index</url-pattern> and in the servlet whereever redirection to the / I changed to /index for the dashboard servlet it is working fine, but how can I make use of the "/" for servlet

I have attached the source code below,

dashboard servlet

package servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@SuppressWarnings("serial")
public class DashboardServlet extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("-->dashboard servlet");
        System.out.println("get method");
        HttpSession session = req.getSession(false);
        if (session != null) {          
            System.out.println("session is available");
            req.getRequestDispatcher("/WEB-INF/welcome.html").forward(req, resp);
        } else {
            System.out.println("no session,");
            resp.sendRedirect("/login");
        }
    }
}

Login Servlet

package servlet;

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

@SuppressWarnings("serial")
public class LoginServlet extends HttpServlet {
    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("-->>>login servlet post method");
        String name = req.getParameter("username");
        String password = req.getParameter("password");
        if (name.equals("admin") && password.equals("password")) {
            HttpSession session = req.getSession();
            session.setAttribute("sessionUserName", name);
            resp.sendRedirect("/");

        } else {
            resp.sendRedirect("/login");
        }
    }

    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        System.out.println("login servlet get method");
        HttpSession session = req.getSession(false);
        if (session != null) {
            System.out.println("request with session");
            resp.sendRedirect("/");
        } else {
            System.out.println("request no session");
            req.getRequestDispatcher("/WEB-INF/login.html").forward(req, resp);
        }

    }
}

web.xml

<web-app>
    <servlet>
        <servlet-name>Login</servlet-name>
        <servlet-class>servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Login</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>Dashboard</servlet-name>
        <servlet-class>servlet.DashboardServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Dashboard</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

appengine-web.xml

<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <application></application>
    <version>1</version>
    <threadsafe>true</threadsafe>
    <system-properties>
        <property name="java.util.logging.config.file" value="WEB-INF/logging.properties" />
    </system-properties>
    <sessions-enabled>true</sessions-enabled>
</appengine-web-app>

login.html

<!DOCTYPE html>
<html>
<head>
<title>Insert title here</title>
</head>
<body>
    <form action="/login" method="post">
        User name :<input type='text' name='username'>Password :<input
            type='password' name='password'><input type='submit'
            value='Submit'>
    </form>
</body>
</html>

welcome.html

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>welcome here
</body>
</html>

Thank you,

1条回答
乱世女痞
2楼-- · 2019-08-01 03:38

You should not check only whether session is null. You should put a value like 'logged_in' into session as attribute. Then, control it for deciding where to route.

Update:

As a quick solution, route doGet inside LoginServlet to doPost and change doPost as below:

   public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        System.out.println("login servlet get method");
        HttpSession session = req.getSession(false);
        if (session != null && session.getAttribute("sessionUserName")!=null) {
            System.out.println("request with session");
            resp.sendRedirect("/");
        } else {

            String name = req.getParameter("username");
            String password = req.getParameter("password");
            if (name.equals("admin") && password.equals("password")) {
                session = req.getSession();
                session.setAttribute("sessionUserName", name);
                resp.sendRedirect("/");

            } else {
               System.out.println("request no session");
                req.getRequestDispatcher("/WEB-INF/login.html").forward(req, resp);
            }

        }

    }
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