Question

I am trying out basic login using JSP and Servlets and don’t understand how forwardslashes are used to indicate the path.

login.JSP is located in LoginApp/WebContent/login.jsp

LoginServlet.java is located in LoginApp/src/org/koushik/javabrains/LoginServlet.java

I have the following code in my login.jsp file –

 <form action="login" method="post">

 <br>User ID  input type="text" name="userId" />
 <br>Password <input type="password" name="password" />
 <br><input type="submit" />

 </form>

The corresponding servlet code is

  @WebServlet("/login")  // <-- forwardslash here
  public class LoginServlet extends HttpServlet 
   {
     private static final long serialVersionUID = 1L;

     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
      {
         String userId, password;

         userId = request.getParameter("userId");
         password = request.getParameter("password");

                 // more code here
      }

    }

If we see the form action, there is no forwardslash before “login”, whereas if we see the servlet annotation, there is a forwardslash before “login”. Why this difference?

Answer 1

In

@WebServlet("/login")

The /login is a url pattern that is relative applications to the contextPath

e.g. if your application had a context path of webapp then a request to

http://localhost:8080/webapp/login would load the LoginServlet

In your jsp the form action

Is relative to the jsp page itself, and not the contextPath.

However because your jsp is located in the webroot folder (the top level folder where your jsp’s and WEB-INF folder live)

http://localhost:8080/webapp/login.jsp

then the action="login" attribute in the form

will resolve to the location

http://localhost:8080/webapp/login

when the form is submitted and will call the LoginServlet

If you move the jsp into a subfolder (e.g. folder1) then action=login will not call the login servlet

as the jsp will now be located at

http://localhost:8080/webapp/subfolder/login.jsp
and so action=login

will now resolve to
http://localhost:8080/webapp/subfolder/login

and the servlet will not be found (remember the login servlet is relative to the context root, thats what the / means in @WebServlet("/login"))

changing the form action to

<form action="../login" method="post">

would work.

To avoid having to work this out in webpage forms

most people will change the form action to look like this

<form action="${pageContext.request.contextPath}/login" method="post">

So that where ever the jsp is located the el expression

${pageContext.request.contextPath}/login

will resolve to same location as the servlet defined with url pattern /login

see What does this expression language ${pageContext.request.contextPath} exactly do in JSP EL? for more info an the el expression

Hope this helps