package org.kodejava.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

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

@WebServlet(urlPatterns = "/context-init-param")
public class ContextInitParameter extends HttpServlet implements Servlet {

    public ContextInitParameter() {
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();

        // Get an instance of ServletContext
        ServletContext context = getServletContext();

        // To read context initialization parameter we can call context.getInitParameter() 
        // and pass the name of initialization parameter to be read. If the named
        // parameter does not exist the returned value will be null.
        //
        // In this example we read an initialization parameter called LOG.PATH
        String logPath = context.getInitParameter("LOG.PATH");
        writer.println("Log Path: " + logPath + "<br/>");

        // Reads all the name of servlet's initialization parameters. If the
        // servlet doesn't have any an empty enumeration will be returned.
        Enumeration<String> enumeration = context.getInitParameterNames();
        while (enumeration.hasMoreElements()) {
            String paramName = enumeration.nextElement();
            String paramValue = context.getInitParameter(paramName);

            writer.println("Context Init Param: [" + paramName + " = " + paramValue +
                    "]<br/>");
        }
    }
}

The context initialization parameter (context-param) look something like this in the web.xml file:

<web-app>
    ...
    <context-param>
        <param-name>locale</param-name>
        <param-value>id_ID</param-value>
    </context-param>
    <context-param>
        <param-name>LOG.PATH</param-name>
        <param-value>F:/Logs</param-value>
    </context-param>
    ...
</web-app>

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>