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WDD_lec_28 - Servlet Lifecycle Lec 28 Servlet Life Cycle...

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Unformatted text preview: Servlet Lifecycle Lec 28 Servlet Life Cycle Time Initialize Service Destroy Life Cycle: Initialize Executed once, when the servlet gets loaded for the first time Not called for each client request Put your initialization code here.(No constructor available) Life Cycle: Service On each request, the server spawns a new thread and calls service() Life Cycle: Service service() checks HTTP request type and calls doGet() or doPost() Override doGet() or doPost()to provide desired behaviour. EE557: ServerSide Development Life Cycle: Service Life Cycle: Destroy destroy() method is called only once Call takes place when Application is stopped Servlet container shuts down Allows resources to be freed EE557: ServerSide Development Servlet Life Cycle Summary Java Servlets Form Data How client sends data? When a user submits a browser request to a web server, it sends two categories of data: Form Data: Data that the user explicitly typed into an HTML form. For example: registration information. HTTP Request Header Data: Data that is automatically appended to the HTTP Request from the client. For example: cookies, browser type, browser IP address. EE557: ServerSide Development Html Form & Servlet HTML is Graphical User Interface (GUI) for a servlet Example : Reading two explicit parameters Form Example Our first example consists of one HTML page (index.html), and one servlet (FormServlet.java). The HTML page contains two form parameters: firstname, surname The Servlet extracts these specific parameters and echoes them back to the browser after appending Hello. index.html EE557: ServerSide Development Form Example (using GET) <html> <head> <title> Reading Two Parameters </title> </head> <body> <H2>Please fill out this form:</H2> <FORM METHOD="GET" ACTION="http://localhost:8080/paramapp/formservlet" NAME="myform"> <BR> Firstname: <INPUT TYPE = "text" NAME="firstname"> <BR> Surname: <INPUT TYPE = "text" NAME="surname"> ........... EE557: ServerSide Development Form Example cont. (using GET) <BR> <INPUT TYPE="submit" value="Submit Form"> <INPUT TYPE="reset" value="Reset"> </FORM> </body> </html> EE557: ServerSide Development FormServlet.java (using GET) import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class MyServlet extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { <input TYPE=""text NAME="firstname"> String fName = req.getParameter("firstname"); String sName = req.getParameter("surname"); PrintWriter out = res.getWriter(); out.println("Hello: " + fName + " " +sName "); out.close(); } } web.xml <?xml version="1.0" encoding="ISO-8859-1"?> <web-app> <servlet> <servlet-name>FormServlet</servlet-name> <servlet-class>MyServlet</servlet-class> </servlet> ACTION="http://localhost:8080/paramapp/formservlet" <servlet-mapping> <servlet-name>FormServlet</servlet-name> <url-pattern>/formservlet</url-pattern> </servlet-mapping> </web-app> Using NetBeans4.1 ...
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