Dynamic Servlet Registration Example

Today I wanted to load a servlet dynamically, and decided to figure out how to do it. It turns out to be really simple.
I created a ServletContextListener and annotated it. In the contextInitialized() method, I set the servlet name, its class, and a mapping and we are done.

We can then deploy the project and watch the magic. Here is the Apache Maven project: dynamic-servlet.zip

ServletContextListenerImpl.java

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/*  * Copyright 2012 Blue Lotus Software, LLC.  * Copyright 2012 John Yeary.  *  * Licensed under the Apache License, Version 2.0 (the "License");  * you may not use this file except in compliance with the License.  * You may obtain a copy of the License at  *  *      http://www.apache.org/licenses/LICENSE-2.0  *  * Unless required by applicable law or agreed to in writing, software  * distributed under the License is distributed on an "AS IS" BASIS,  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  * See the License for the specific language governing permissions and  * limitations under the License.  */ package com.bluelotussoftware.servlet;   import java.util.Map; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import javax.servlet.ServletRegistration; import javax.servlet.annotation.WebListener;   /**  *  * @author John Yeary  * @version 1.0  */ @WebListener public class ServletContextListenerImpl implements ServletContextListener {       @Override     public void contextInitialized(final ServletContextEvent sce) {         final ServletContext servletContext = sce.getServletContext();         final ServletRegistration.Dynamic dynamic = servletContext.addServlet("Example Servlet", ExampleServlet.class);         dynamic.addMapping("/");           final Map<String, ? extends ServletRegistration> map = servletContext.getServletRegistrations();         for (String key : map.keySet()) {             servletContext.log("Registered Servlet: " + map.get(key).getName());         }     }       @Override     public void contextDestroyed(final ServletContextEvent sce) {         //NO-OP     } }

ExampleServlet.java

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/*  * Copyright 2012 Blue Lotus Software, LLC.  * Copyright 2012 John Yeary.  *  * Licensed under the Apache License, Version 2.0 (the "License");  * you may not use this file except in compliance with the License.  * You may obtain a copy of the License at  *  *      http://www.apache.org/licenses/LICENSE-2.0  *  * Unless required by applicable law or agreed to in writing, software  * distributed under the License is distributed on an "AS IS" BASIS,  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  * See the License for the specific language governing permissions and  * limitations under the License.  */ package com.bluelotussoftware.servlet;   import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;   /**  *  * @author John Yeary  * @version 1.0  */ public class ExampleServlet extends HttpServlet {       /**      * Processes requests for both HTTP      * <code>GET</code> and      * <code>POST</code> methods.      *      * @param request servlet request      * @param response servlet response      * @throws ServletException if a servlet-specific error occurs      * @throws IOException if an I/O error occurs      */     protected void processRequest(HttpServletRequest request, HttpServletResponse response)             throws ServletException, IOException {         response.setContentType("text/html;charset=UTF-8");         PrintWriter out = response.getWriter();         try {             out.println("<html>");             out.println("<head>");             out.println("<title>Servlet ExampleServlet</title>");             out.println("</head>");             out.println("<body>");             out.println("<h1> Servlet ExampleServlet at " + request.getContextPath() + "</h1> ");             out.println("<p style=\"font-size:24px;font-weight:bold;\"> Hello World!</p> ");             out.println("</body>");             out.println("</html>");         } finally {             out.close();         }     }       /**      * Handles the HTTP      * <code>GET</code> method.      *      * @param request servlet request      * @param response servlet response      * @throws ServletException if a servlet-specific error occurs      * @throws IOException if an I/O error occurs      */     @Override     protected void doGet(HttpServletRequest request, HttpServletResponse response)             throws ServletException, IOException {         processRequest(request, response);     }       /**      * Handles the HTTP      * <code>POST</code> method.      *      * @param request servlet request      * @param response servlet response      * @throws ServletException if a servlet-specific error occurs      * @throws IOException if an I/O error occurs      */     @Override     protected void doPost(HttpServletRequest request, HttpServletResponse response)             throws ServletException, IOException {         processRequest(request, response);     } }