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import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;

@WebServlet("/configDemo")
public class ConfigDemoServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        // You can retrieve ServletConfig parameters here
        String initParam = config.getInitParameter("exampleParam");
        System.out.println("ServletConfig exampleParam: " + initParam);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        response.setContentType("text/html");
        String contextParam = getServletContext().getInitParameter("contextParam");
        ServletContext context = getServletContext();
        
        response.getWriter().println("<html><body>");
        response.getWriter().println("<h1>ServletConfig and ServletContext Demo</h1>");
        response.getWriter().println("<p>ServletConfig Parameter: " + 
                request.getServletContext().getInitParameter("contextParam") + "</p>");
        response.getWriter().println("<p>ServletContext Parameter: " + 
                contextParam + "</p>");
        response.getWriter().println("</body></html>");
    }
}
 web.xml
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
         http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" 
         version="3.1">

    <servlet>
        <servlet-name>ConfigDemoServlet</servlet-name>
        <servlet-class>ConfigDemoServlet</servlet-class>
        <init-param>
            <param-name>exampleParam</param-name>
            <param-value>This is a ServletConfig parameter</param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>ConfigDemoServlet</servlet-name>
        <url-pattern>/configDemo</url-pattern>
    </servlet-mapping>

    <context-param>
        <param-name>contextParam</param-name>
        <param-value>This is a ServletContext parameter</param-value>
    </context-param>
</web-app>
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