NullPointer Exception for ServletContext

package sl314.view;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletContext;
// Support classes
import java.io.IOException;
import java.io.PrintWriter;
// Model classes
import sl314.model.League;
import java.util.List;
import java.util.Iterator;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;

public class ListLeaguesServlet extends HttpServlet {

//private List leagueList = null;
    List leagueList=null;

@Override
    public void init(ServletConfig cfg) throws ServletException
    {
        super.init(cfg);
        ServletContext context=getServletContext();
        leagueList = (List) context.getAttribute("leagueList");
    }
    
    @Override
    public void doGet(HttpServletRequest request,
            HttpServletResponse response)
            throws IOException {
        PrintWriter out = response.getWriter();
       
        try{

// Create the set of leagues
            /*
       leagueList = new LinkedList();
       leagueList.add( new League(2003, "Spring","Soccer League (Spring '03)") );
       leagueList.add( new League(2003, "Summer","Summer Soccer Fest 2003") );
       leagueList.add( new League(2003, "Fall","Fall Soccer League (2003)") );
       leagueList.add( new League(2004, "Spring","Soccer League (Spring '04)") );
       leagueList.add( new League(2004, "Summer","The Summer of Soccer Love 2004") );
       leagueList.add( new League(2004, "Fall","Fall Soccer League (2004)") );
        */
        // Set page title
        String pageTitle = "Duke's Soccer League: List Leagues";
        
        // Retrieve the list of leagues from the context-scope

out.println(getServletContext().getAttribute("leagueList")); 
                  ======> prints as null in output.....
        
        // Specify the content type is HTML
        response.setContentType("text/html");
        
        
        // Generate the HTML response
        out.println("<html>");
        out.println("<head>");
        out.println("  <title>" + pageTitle + "</title>");
        out.println("</head>");
        out.println("<body bgcolor='white'>");
        
        // Generate page heading
        out.println("");
        out.println("<table border='1' cellpadding='5' cellspacing='0' width='400'>");
        out.println("<tr bgcolor='#CCCCFF' align='center' valign='center' height='20'>");
        out.println("  <td><h3>" + pageTitle + "</h3></td>");
        out.println("</tr>");
        out.println("</table>");
        
        // Generate main body
        out.println("<p>");
        out.println("The set of soccer leagues are:");
        out.println("</p>");
        
        
        
        if ( leagueList !=null)
        {
            Iterator items = leagueList.iterator();
            out.println("<ul>");
        while ( items.hasNext() ) {
            League league = (League) items.next();
            out.println("  <li>" + league.getTitle() + "</li>");
        }
        out.println("</ul>");
            }
        out.println("</body>");
        out.println("</html>");
        }
        catch(Exception e)
        {
            out.println(e);
        }
    }
}

I get a NullPointer Exception .... the leagues-file is not getting populated from the context....not sure why....can anyone check to try any modifications..?

The ServletContextListener is as follows:
============================

package sl314.util;

import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;
// Support classes
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.BufferedReader;
// Model classes
import sl314.model.League;
import java.util.List;
import java.util.LinkedList;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;

public class InitializeLeagues implements ServletContextListener {

@Override
    public void contextInitialized(ServletContextEvent event) {

ServletContext context = event.getServletContext();
        
        String leaguesFile = context.getInitParameter("leagues-file");
        List leagueList = new LinkedList();
        InputStream is = null;
        BufferedReader reader = null;
        
        try {
            is = context.getResourceAsStream(leaguesFile);
            reader = new BufferedReader(new InputStreamReader(is));
            String record;
            
            // Read every record (one per line)
            while ( (record = reader.readLine()) != null ) {
                String[] fields = record.split("\t");
                
                // Extract the data fields for the record
                int year = Integer.parseInt(fields[0]);
                String season = fields[1];
                String title = fields[2];
                
                // Add the new League item to the list
                League item = new League(year, season, title);
                leagueList.add(item);
            }
            
            context.setAttribute("leagueList", leagueList);
            
            context.log("The league list has been loaded.");
            
        } catch (Exception e) {
            context.log("Exception occured while processing the leagues file.", e);
            
        } finally {
            if ( is != null ) {
                try { is.close(); } catch (Exception e) {}
            }
            if ( reader != null ) {
                try { reader.close(); } catch (Exception e) {}
            }
        }
        
    } // END of contextInitialized
    
    @Override
    public void contextDestroyed(ServletContextEvent event) {
        // do nothing
    }
    
} // END of InitializeLeagues class

===============================================================

My web.xml file is as follows :
======================================

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    <display-name>SL-314 WebApp Example</display-name>
    <description>
    This Web Application demonstrates using the context-scope to store
    a common resource: the "leagueList" for the Soccer League webapp.
  </description>
    <context-param>
        <param-name>leagues-file</param-name>
        <param-value>/WEB-INF/data/leagues.txt</param-value>
    </context-param>
    <listener>
        <listener-class>sl314.web.InitializeLeagues</listener-class>
    </listener>
    <servlet>
        <servlet-name>ListLeagues</servlet-name>
        <servlet-class>sl314.view.ListLeaguesServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>AddLeagueForm</servlet-name>
        <servlet-class>sl314.view.AddLeagueFormServlet</servlet-class>
        <init-param>
            <param-name>seasons-list</param-name>
            <param-value>Spring,Summer,Autumn,Winter</param-value>
        </init-param>
    </servlet>
    <servlet>
        <servlet-name>AddLeague</servlet-name>
        <servlet-class>sl314.controller.AddLeagueServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>Success</servlet-name>
        <servlet-class>sl314.view.SuccessServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ListLeagues</servlet-name>
        <url-pattern>/list_leagues.view</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>AddLeagueForm</servlet-name>
        <url-pattern>/admin/add_league.view</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>AddLeague</servlet-name>
        <url-pattern>/admin/add_league.do</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>Success</servlet-name>
        <url-pattern>/admin/success.view</url-pattern>
    </servlet-mapping>
</web-app>

Awaiting reply...

[Added code tags - see UseCodeTags for details]

Hi Bindu. Welcome to the Ranch!

bindu sadanandan wrote:I get a NullPointer Exception .... the leagues-file is not getting populated from the context....not sure why....can anyone check to try any modifications..?

Awaiting reply...

Where do you get it? The error message will tell you exactly which line it happened on, and you're likely to get a useful reply if you tell us.

(You're also more likely to get one in the Servlets forum, so I've moved the post there).

I am trying to get content stored in global context parameter "leagues-file" that points to /WEB-INF/data/leagues.txt ..... the leagues.txt has the following contents

2003 Summer Summer Here

each corresponding to year,season and title ...... so I read the leagues.txt record by record by using ServletContext to get the file and read using BufferedReader...

ServletContext context = event.getServletContext();

String leaguesFile = context.getInitParameter("leagues-file");
List leagueList = new LinkedList();
InputStream is = null;
BufferedReader reader = null;

try {
is = context.getResourceAsStream(leaguesFile);
reader = new BufferedReader(new InputStreamReader(is));
String record;

// Read every record (one per line)
while ( (record = reader.readLine()) != null ) {
String[] fields = record.split("\t");

// Extract the data fields for the record
int year = Integer.parseInt(fields[0]);
String season = fields[1];
String title = fields[2];

// Add the new League item to the list
League item = new League(year, season, title);
leagueList.add(item);
}

context.setAttribute("leagueList", leagueList);

The year,season and title are passed to the League model constructor League item = new League(year, season, title); tat works fine.

And passed the leagueList as context attribute context.setAttribute("leagueList", leagueList);

But when I get the Attribute in my ListLeaguesServlet.java

ServletContext context=getServletContext();
leagueList = (List) context.getAttribute("leagueList");

the leagueList is showing null even though my leagues.txt file has contents... i chked null output by line 54

out.println(getServletContext().getAttribute("leagueList"));
======> prints as null in output.....

If I remove the if loop to see the Exception

// if ( leagueList !=null)
//{
Iterator items = leagueList.iterator();
out.println("<ul>");
while ( items.hasNext() ) {
League league = (League) items.next();
out.println(" <li>" + league.getTitle() + "</li>");
// }

The output will be :

null
Duke's Soccer League: List Leagues

The set of soccer leagues are:

java.lang.NullPointerException

============================

The first null was to chk the value of out.println(getServletContext().getAttribute("leagueList"));

Can anyone figure out why the ListLeaguesServlet.java is listing the contents that I enter in the context parameter file leagues.txt ?

Can anyone figure out why the ListLeaguesServlet.java is not*listing the contents that I enter in the context parameter file leagues.txt ?

Since leagueList has a list of values try this getAttributeNames() instead of getAttribute() it comes under java.util.Enumeration Now iterate it you will get the values

I need to use Enumeration in order to retrieve more than one context-parameters right ? But I only have one context parameter

Context Parameter

Parameter Name Parameter Value
leagues-file /WEB-INF/data/leagues.txt

The league.txt has single line with multiple columns separated by tab.For this I have used below code in order to retrieve multiple values

while ( (record = reader.readLine()) != null ) {
String[] fields = record.split("\t");

// Extract the data fields for the record
int year = Integer.parseInt(fields[0]);
String season = fields[1];
String title = fields[2];

// Add the new League item to the list
League item = new League(year, season, title);
leaguelist.add(item);

here I have only one context-parameter leagues-file pointing to leagues.txt...

I have multiple entries in leagues.txt ...

The leaguelist here i passed as context.setAttribute("leagueList", leagueList); line 52 ( I passed a list name leagueList (right ) as object and gave it a random name "leagueList"(left) which is String )

context.setAttribute( String string , Object object )

In my listleaguesServlet.java when I get the attribute from ServletContext still there is only one attribute that I set leagueList(left) which is String ( string can have multiple entries )and I have typecasted

leagueList = (List) context.getAttribute("leagueList"); line 27

I have used iterator to list the values of list leagueList (left) which i got after typecasting.

The below code is to get multiple context-parameters

String value=null;

Enumeration e=getServletContext().getInitParameterNames();
while(e.hasMoreElements())
{
value=getServletContext().getInitParameter((String) e.nextElement());
out.println(value + "<br>");
}

which will give /WEB-INF/data/leagues.txt as output

But I only have a single context parameter..........can you tell me where exactly you want me to use Enumeration?......

dear bindu
please try to some comments............ and indents............ its very hard to read ................. this is not history right keep the things small and easily.............................

Your code seems fine.....I think there is some problem with the following statement

String[] fields = record.split("\t");

Either your file is not properly delimited or there is some problem with "\t".....Please check...