diff --git a/javax-servlets/src/main/java/com/baeldung/filters/EmptyParamFilter.java b/javax-servlets/src/main/java/com/baeldung/filters/EmptyParamFilter.java
new file mode 100644
index 0000000000..b0b5392237
--- /dev/null
+++ b/javax-servlets/src/main/java/com/baeldung/filters/EmptyParamFilter.java
@@ -0,0 +1,35 @@
+package com.baeldung.filters;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.annotation.WebFilter;
+import java.io.IOException;
+
+@WebFilter(urlPatterns = "/uppercase")
+public class EmptyParamFilter implements Filter {
+
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+    }
+
+    @Override
+    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
+        FilterChain filterChain) throws IOException, ServletException {
+        String inputString = servletRequest.getParameter("input");
+
+        if (inputString != null && inputString.matches("[A-Za-z0-9]+")) {
+            filterChain.doFilter(servletRequest, servletResponse);
+        } else {
+            servletResponse.getWriter().println("Missing input parameter");
+        }
+    }
+
+    @Override
+    public void destroy() {
+    }
+
+}
diff --git a/javax-servlets/src/main/java/com/baeldung/listeners/AppListener.java b/javax-servlets/src/main/java/com/baeldung/listeners/AppListener.java
new file mode 100644
index 0000000000..ed16dd1654
--- /dev/null
+++ b/javax-servlets/src/main/java/com/baeldung/listeners/AppListener.java
@@ -0,0 +1,21 @@
+package com.baeldung.listeners;
+
+import javax.servlet.ServletContext;
+import javax.servlet.ServletContextEvent;
+import javax.servlet.ServletContextListener;
+import javax.servlet.annotation.WebListener;
+
+@WebListener
+public class AppListener implements ServletContextListener {
+
+    @Override
+    public void contextInitialized(ServletContextEvent event) {
+        ServletContext context = event.getServletContext();
+        context.setAttribute("counter", 0);
+    }
+
+    @Override
+    public void contextDestroyed(ServletContextEvent event) {
+
+    }
+}
diff --git a/javax-servlets/src/main/java/com/baeldung/listeners/RequestListener.java b/javax-servlets/src/main/java/com/baeldung/listeners/RequestListener.java
new file mode 100644
index 0000000000..7f0c37b666
--- /dev/null
+++ b/javax-servlets/src/main/java/com/baeldung/listeners/RequestListener.java
@@ -0,0 +1,24 @@
+package com.baeldung.listeners;
+
+import javax.servlet.ServletContext;
+import javax.servlet.ServletRequestEvent;
+import javax.servlet.ServletRequestListener;
+import javax.servlet.annotation.WebListener;
+import javax.servlet.http.HttpServletRequest;
+
+@WebListener
+public class RequestListener implements ServletRequestListener {
+
+    @Override
+    public void requestInitialized(ServletRequestEvent event) {
+    }
+
+    @Override
+    public void requestDestroyed(ServletRequestEvent event) {
+        HttpServletRequest request = (HttpServletRequest)event.getServletRequest();
+        if (!request.getServletPath().equals("/counter")) {
+            ServletContext context = event.getServletContext();
+            context.setAttribute("counter", (int)context.getAttribute("counter") + 1);
+        }
+    }
+}
diff --git a/javax-servlets/src/main/java/com/baeldung/servlets/CounterServlet.java b/javax-servlets/src/main/java/com/baeldung/servlets/CounterServlet.java
new file mode 100644
index 0000000000..a11f084db2
--- /dev/null
+++ b/javax-servlets/src/main/java/com/baeldung/servlets/CounterServlet.java
@@ -0,0 +1,21 @@
+package com.baeldung.servlets;
+
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.io.PrintWriter;
+
+@WebServlet(urlPatterns = "/counter", name = "counterServlet")
+public class CounterServlet extends HttpServlet {
+
+    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
+        PrintWriter out = response.getWriter();
+
+        int count = (int)request.getServletContext().getAttribute("counter");
+
+        out.println("Request counter: " + count);
+    }
+
+}
diff --git a/javax-servlets/src/main/java/com/baeldung/servlets/UppercaseServlet.java b/javax-servlets/src/main/java/com/baeldung/servlets/UppercaseServlet.java
new file mode 100644
index 0000000000..766ec2e6ff
--- /dev/null
+++ b/javax-servlets/src/main/java/com/baeldung/servlets/UppercaseServlet.java
@@ -0,0 +1,20 @@
+package com.baeldung.servlets;
+
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.io.PrintWriter;
+
+@WebServlet(urlPatterns = "/uppercase", name = "uppercaseServlet")
+public class UppercaseServlet extends HttpServlet {
+
+    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
+        String inputString = request.getParameter("input").toUpperCase();
+
+        PrintWriter out = response.getWriter();
+
+        out.println(inputString);
+    }
+}