Java ServletContext

Question

I have a JSP web site, not Spring MVC, and it has a config file web.xml.

There are a couple of settings within the web.xml file that I\'d like to get.

However, I

Answer 1

I really don't like classes reading from web.xml... Why do you need that? IMHO it would be easier, cleaner and by far much more manageable if you prepared a properties file and a manager class that reads from there.

Answer 2

I think this is very close to your description: link.

Basically, you want to read parameters from web.xml programatically, right?

Answer 3

This is not easily possible and may not be an elegent solution. The only option I can suggest is to have your configuration options i a xml or properties file and put it in your WEB-INF/classes directory so you can look it up using ClassLoader.getResource or ClassLoader.getResourceAsStream

I know it may be a duplication of the configuration, but IMO its the elegent way.

Answer 4

Using a javax.servlet.ServletContextListener implementation, that allows a singleton-like access to context:

package test.dummy;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;

public  class ContextConfiguration implements ServletContextListener {

  private static ContextConfiguration _instance;

  private ServletContext context = null;

  //This method is invoked when the Web Application
  //is ready to service requests
  public void contextInitialized(ServletContextEvent event) {
    this.context = event.getServletContext();

    //initialize the static reference _instance
     _instance=this;
  }

  /*This method is invoked when the Web Application has been removed 
  and is no longer able to accept requests
  */
  public void contextDestroyed(ServletContextEvent event) {
    this.context = null;

  }

  /* Provide a method to get the context values */
  public String getContextParameter(String key) {
     return this.context.getInitParameter(key);
  }

  //now, provide an static method to allow access from anywere on the code:
  public static ContextConfiguration getInstance() {
     return _instance;
  }
}

Set it up at web.xml:

<web-app>
<listener>
    <listener-class>
     test.dummy.ContextConfiguration
    </listener-class>
  </listener>
<servlet/>
<servlet-mapping/>
</web-app> 

And use it from anywhere at the code:

ContextConfiguration config=ContextConfiguration.getInstance();
String paramValue=config.getContextParameter("parameterKey");

Answer 5

Hmmm... I am assuming that once your web app is up then you are not going to make any change in the web.xml....

Now what you can do is a create a servlet which loads on the startup and initialize a singleton class. You can use the following setting in your web.xml.

  <servlet>
    <description></description>
    <display-name>XMLStartUp</display-name>
    <servlet-name>XMLStartUp</servlet-name>
    <servlet-class>com.test.servlets.XMLStartUp</servlet-class>
    <init-param>
      <param-name>log4j-init-file</param-name>
      <param-value>WEB-INF/classes/log4j.properties</param-value>
    </init-param>
    <load-on-startup>0</load-on-startup>
  </servlet>

In tomcat if you set load-on-startup value 0, then it means that while loading it has got the highest priority. now in the servlets init method read all the init-parameters like this and set it in your singleton class.

String dummy= getInitParameter("log4j-init-file");