feat: restructure docs into "chapters" (#12)

* feat(docker, k8s): create containers folder and kubernetes notes

docs/languages/java/web/servlet.md

@@ -0,0 +1,51 @@
+# Servlet
+
+A Java servlet is a Java software component that extends the capabilities of a server.
+Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applications on web servers and thus qualify as a server-side servlet web API.
+
+## Basic Structure
+
+```java
+package <package>;
+
+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;
+
+@WebServlet("/route")
+public class <className> extends HttpServlet {
+    private static final long serialVersionUID = 1L;
+
+    /** handle get request */
+    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+
+        // GET REQUEST: load and display page (forward to JSP)
+        // OPTIONAL: add data to request (setAttribute())
+
+    }
+
+    /** handle post request */
+    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+
+        // POST REQUEST: add stuff to DB, page, ...
+
+        doGet(request, response);  // return same page with new  content added (default case)
+    }
+}
+```
+
+## Servlet Instructions
+
+```java
+request.getParameter()  // read request parameter
+
+response.setContentType("text/html");  // to return HTML in the response
+
+response.getWriter().append("");  //append content to the http response
+
+request.setAttribute(attributeName, value);  // set http attribute of the request
+request.getRequestDispatcher("page.jsp").forward(request, response);  // redirect the request to another page
+```