Question

Hello i have a question about servlet calling another servlet

I have a main servlet called Relay which is going to be responsible to control the other servlets

the user will click on and will be forwarded to Relay servlet

<li><a href="/oosd/Relay?selectAnimal=SelectAnimalServlet">Check the available animals</a> </li>

inside Relay servlet will get the value of the parameter to determine which servlet is going to run

String selectAnimal = request.getParameter("selectAnimal");

if (selectAnimal.equals("SelectAnimalServlet")){
            getServletContext().getNamedDispatcher("/SelectAnimalServlet") 
            .forward(request, response); 
            //for testing
            System.out.println("Request forwarded to " + selectAnimal + " servlet");
        }

SelectAnimalServlet code:

try
{     
    HttpSession session = request.getSession(true);
    session.getAttribute("currentSessionUser");
    List<AnimalSelectBean> beans = DAO.getAnimalList(); 
    request.setAttribute("beans", beans); 
    request.getRequestDispatcher("CheckAnimal.jsp").forward(request, response); 


}

Now when i run that it’s not working for some reason, if i change the link to SelectAnimalServlet directly the code works any idea how to solve this ?

Edit:

Here is my web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:javaee="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>content.LoginServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>UpdateAnimalServlet</servlet-name>
    <servlet-class>content.UpdateAnimalServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>SelectAnimalServlet</servlet-name>
    <servlet-class>content.SelectAnimalServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>Relay</servlet-name>
    <servlet-class>content.Relay</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>SelectAnimalServlet</servlet-name>
    <url-pattern>/SelectAnimalServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>UpdateAnimalServlet</servlet-name>
    <url-pattern>/UpdateAnimalServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>Relay</servlet-name>
    <url-pattern>/Relay</url-pattern>
  </servlet-mapping>
</web-app>

also I changed:

getServletContext().getNamedDispatcher("/SelectAnimalServlet") 
                .forward(request, response); 

to:

response.sendRedirect(response.encodeRedirectURL(selectAnimal));

and still the same thing blank webpage with http://localhost:8080/oosd/Relay?selectAnimal=SelectAnimalServlet link

Answer 1

getNamedDispatcher expects a servlet name; you’re providing it with a servlet URL.

Either use the name, or use getRequestDispatcher with the URL.

Since you’re forwarding, the URL will not change–there is no redirect response sent back to the browser on a forward. The contents of the forward are written directly to the original response.

Now that you’re forwarding, you need to redirect to the URL, not just the name of the servlet.

What does the servlet you redirect to do for output?

I don’t believe your parameter naming convention makes any sense. The parameter shouldn’t be named the same as a servlet name; the parameter should be something like “command” or “select”. You would then use the command parameter value to look up the URL of the servlet. Or, in your case, just prepend a /, and you’re done. There’s no need to do any if/else comparisons.