Java Servlets

1. Java Servlets Lec 27

2. Creating a SimpleWeb Application in Tomcat

3. Tomcat Directory Structure myapp

4. Tomcat Setup Folder for HTML and JSP pages Folder for servlet and other java classes

5. Servlet Types • Servlets are based on two main packages • javax.servlet • javax.servlet.http • GenericServlet • For writing protocol independent servlets • HttpServlet • Extends from GenericServlet class • Adds functionality for writing HTTP specific servlets

6. Servlet class hierarchy Object GenericServlet ServerRequest ServletResponse javax.servlet HttpServlet HttpServletRequest HttpServletResponse javax.servlet.http

7. Writing Servlet • Every servlet must implement the javax.servlet.Servlet interface • Contains the servlet’s life cycle methods etc. • These are implemented by GenericServlet and HttpServlet classes • Extend your servlet from one of these classes and add your own functionality public class MyServlet extends GenericServlet public class HelloServlet extends HttpServlet

8. Types of HTTP Requests • Get • Post • Delete • Options • Put • Trace

9. Servlets How HTTP Sends Request • Some HTTP request types • Get -- Attr/Val pairs attached after ? of URL • E.g. http://www.gmail.com/register?name=ali • Post -- Attr/Val pairs attatched with the request body Client Server

10. HTTP Request Example Request parameters etc

11. Writing Servlet Steps for making a HelloWorldServlet • Create a directory structure for your application (myapp). This is a one time process for any application • Create a HelloWorldServlet source file by extending this class from HttpServlet and override your desired method • Compile it (If compiler complains of not having required packages, check your class paths)

12. Writing Servlet Steps for making a HelloWorldServlet • Place the class file in the classes folder of your webapplication. (myapp) If you are using packages (recommended) then create a complete directory structure under classes folder • Create a deployment descriptor (web.xml) and put it inside WEB-INF folder • Restart your server, if already running • Access your application using Web browser

13. HelloServlet Example Code

14. HelloWorldServlet import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorldServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); out.println(“Hello World!”); } }

15. web.xml <?xml version="1.0" encoding="ISO-8859-1"?> <web-app> <servlet> <servlet-name>HelloWorldServlet</servlet-name> <servlet-class>HelloWorldServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>HelloWorldServlet</servlet-name> <url-pattern>/myfirstservlet</url-pattern> </servlet-mapping> </web-app>

16. Compiling and Invoking Servlets • Compile HelloWorldServlet.javausing javac command • Put HelloWorldServlet class in install_dir/webapps/myapp/WEB-INF/classes • Put web.xml file in install_dir/webapps/myapp/WEB-INF • Invoke your servlet by writing following command in the web browser http://localhost:8080/myapp/myfirstservlet

17. Lets do it LIVE

18. Free Servlet and JSP Engines • Apache Tomcat • http://jakarta.apache.org/tomcat/ • Allaire/Macromedia JRun • http://www.allaire.com/products/jrun • New Atlanta ServletExec • http://www.servletexec.com • Causho’s Resin • http://www.caucho.com