无法从web.xml中读取上下文参数

Question

I am writing a J2EE web application with NetBeans running in Tomcat 7.0.41. I've created a deployment descriptor, web.xml, with four context-params in it. I've created a class that extends HttpServlet. In the init method for the class, when I call getInitParameterNames from the ServletConfig instance, I get an empty enumeration. Ultimately, I suspect Tomcat isn't reading the web.xml file at all because I had to resort to using the @WebServlet annotation to even reach the servlet at all. Can anyone suggest why I can't access the context-params and/or why Tomcat isn't reading the web.xml file?

Here is the web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<context-param>
    <param-name>preptimeminutes</param-name>
    <param-value>60</param-value>
</context-param>
<context-param>
    <param-name>preptimehours</param-name>
    <param-value>0</param-value>
</context-param>
<context-param>
    <param-name>servings</param-name>
    <param-value>1</param-value>
</context-param>
<context-param>
    <param-name>calories</param-name>
    <param-value>100</param-value>
</context-param>
<session-config>
    <session-timeout>
        30
    </session-timeout>
</session-config>

Here is the code for the init method:

@Override
public void init(ServletConfig servletConfig) throws ServletException
{
    int preptemp;
    String tempString1, tempString2;
    Enumeration<String> e = servletConfig.getInitParameterNames();

this.servletConfig = servletConfig;
    servletContext = servletConfig.getServletContext();

    try 
    {
        while(e.hasMoreElements())
        {
           servletContext.log(e.nextElement());       
        }
    } ...
}

Thanks,

Jason Mazzotta

Answer 1

It seems that you want to read parameters of ServletContex (the ones for entire application), but you ended up with reading ServletConfig (the ones for specific servlet).

Another potential problem is that you are overriding init(ServletConfig) instead of init() . First method shouldn't be overridden because it handles many servlet life cycle tasks like adding servlet to available servlets pool. If you want to add something to initialization process you should override init() method which is invoked later by init(ServletConfig) .

So try maybe something like

@Override
public void init() throws ServletException
{
    ServletContext servletContext = getServletContext();
    Enumeration<String> e = servletContext.getInitParameterNames();
    try 
    {
        while(e.hasMoreElements())
        {
           servletContext.log(e.nextElement());       
        }
    } ...
}