Significance of context param in web.xml to initialize any variable?servlet

Question

I am writing a standalone web appplication for rss (xml) creation where i am having jsp servlets class etc.
Now to write rss.xml and read it back in application i have temporarily used c:\\rss.xml but to make it capable working in web application which can be uploaded in website i need to make it configurable i need to kep it in context param of web.xml and in init() method of servlet of my application what exactly i should do there.what i have tried is this :
public class Startup extends HttpServlet {
private static String rssFeed;
private ServletContext ctx;
Logger log = Logger.getLogger(Startup.class);
public void init(){
log.debug("Initializing APPLICATION CONTEXT Variables");
ctx = getServletContext();
rssFeed = (String)ctx.getInitParameter("RssFeed");
log.debug("Rss : " + rssFeed);
String rssFile = this.getServletContext().getRealPath("") + File.separator + "WEB-INF" + File.separator + "rss.properties";
Properties property = new Properties();
try{
InputStream propertiesFile = new FileInputStream(rssFile);
property.load(propertiesFile);
catch (IOException e) {
log.error("IOException during domainValuesList file Reading");
e.printStackTrace();
log.error("Exception while loading AllowedDomainValues file");
log.debug("Domain Values Lists Updated");
/** Get Host Name (Server Name) where application is hosted on
public static String getRssFeed(){
return rssFeed;
after that i called this startup servlet class in other servlet taken this getRssFeed()
stored it as string passed as parametr to other class where i need to call it but there i am getting null pointer exception which says not initialized.
even what i have written in web.xml is here:
<context-param>
<param-name>RssFeed</param-name>
<param-value>c:\\rsshandler.xml</param-value>
</context-param>
<servlet>
<servlet-name>Startup</servlet-name>
<servlet-class>src.Startup</servlet-class>
<init-param>
<param-name>RssFeedConfig</param-name>
<param-value>/WEB-INF/rss-config.xml</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>Startup</servlet-name>
<url-pattern>/Startup</url-pattern>
<load-on-startup>1</load-on-startup>
</servlet-mapping>
i tried what i know or understood but its not working.
one more thing i have doneis:created rss.properties files in web-inf
lines added are
rssfeed=c:\\rsshandler.xml
but even i am not getting this why
or what sholud i do here.
this thing needs to be configurablewhich we can change later easily.
any suggestions.
thanks
vijendra

Answer 1

Ben -
There can be init params for the servlet or for the servlet context. For the servlet, this looks like:
<servlet>
<servlet-name>InitServlet</servlet-name>
<servlet-class>package1.InitServlet</servlet-class>
<init-param>
<param-name>message</param-name>
<param-value>Hello From Initialization Parameter</param-value>
</init-param>
</servlet>
in the web.xml file, and is accessed using:
public void init(ServletConfig config) throws ServletException
super.init(config);
message = config.getInitParameter("message");
For a servlet context init param, you define it as you did using the web.xml settings editor:
<context-param>
<param-name>hello</param-name>
<param-value>hi</param-value>
</context-param>
This is accessed using:
public void init(ServletConfig config) throws ServletException
super.init(config);
message1 = config.getServletContext().getInitParameter("hello");
Hope this helps,
Lynn
Java Tools Team