Question

Hi if someone could look at my code and maybe see something I am not, this is for a lab for a class assignment of mine. Thank you!

I am programming a simple servlet in a dynamic web project using eclipse. One of the labs requirements is to grab an init parameter from the web.xml in a Servlet.

When I try to get the value of an init-param in my servlet. It keeps returning null.

Anyone see anything wrong that I am not:

im using command:

this.getServletConfig().getInitParameter("title");

In class ConvertServlet that is in a00730628.controller package with in the doPost function. I also tried from the init function but got null there to, so I am thinking there is an error in my xml. I am using version 3.0 and Tomcat 7.26

And here is my web.xml:

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

<display-name>lab10</display-name>

<welcome-file-list>

<welcome-file>index.html</welcome-file>

<welcome-file>index.htm</welcome-file>

<welcome-file>index.jsp</welcome-file>

<welcome-file>default.html</welcome-file>

<welcome-file>default.htm</welcome-file>

<welcome-file>default.jsp</welcome-file>

</welcome-file-list>



<servlet>

<servlet-name>ConvertServlet</servlet-name> 

<servlet-class>a00730628.controller.ConvertServlet</servlet-class>



<init-param>

  <param-name>title</param-name>

  <param-value>Temperature Converter Result</param-value>

</init-param>

</servlet>

</web-app>

Edit added my Servlet Code:

package a00730628.controller;

import java.io.IOException;


import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import a00730628.util.TemperatureConverter;
import a00730628.view.Lab10Html;

/**
 * Servlet implementation class ConvertServlet
 */
@WebServlet("/convert")
public class ConvertServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final int CEL_2_FAR = 0;
    private static final int FAR_2_CEL = 1;

    private String resultTitle = "";

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ConvertServlet() {
        super();
        // TODO Auto-generated constructor stub
    }


    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().println("<a href='index.html'>Please make a post request from here</a>");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        try {
            resultTitle = this.getServletConfig().getInitParameter("title");
            if (resultTitle == null) {
                response.sendError(500, "Title param is null ... wa wa wa");
                return;
            }
            int type = Integer.parseInt(request.getParameter("type"));
            double number = Double.parseDouble(request.getParameter("number"));
            double converted;
            String result = "";
            switch (type) {
                case CEL_2_FAR:
                    converted = TemperatureConverter.celsiusToFarenheit(number);
                    result = String.format("%f celsius = %f farenheit", number, converted);
                    break;
                case FAR_2_CEL:
                    converted = TemperatureConverter.farenheitToCelsius(number);
                    result = String.format("%f farenheit = %f celsius", number, converted);
                    break;

            }
            response.getWriter().print(Lab10Html.getLab10Html(resultTitle, result));
        } catch (NumberFormatException e) {
            response.sendError(400, "Please enter a number like 42. Number format error: "+ e.getMessage());
        }


    }

}

Answer 1

You are using the annotations in the servlet. To add the init parameter using annotations,follow the following syntax and remove the servlet configarations in web.xml.

@WebServlet(name = "convert", urlPatterns = {"/convert"},
  initParams = {@WebInitParam(name="title", value="Temperature Converter Result")}
)

If you don’t want to use annotations remove @WebServlet("/convert") from the servlet class.