JAVA SERVLET. Server-side Programming INTRODUCTION

Transcription

1 JAVA SERVLET Server-side Programming INTRODUCTION 1

2 AGENDA Introduction Java Servlet Web/Application Server Servlet Life Cycle Web Application Life Cycle Servlet API Writing Servlet Program Summary 2

3 INTRODUCTION Web server response can be static or dynamic Static: HTML document is retrieved from the file system and returned to the client Dynamic: HTML document is generated by a program in response to an HTTP request 3

4 JAVA SERVLET (CONT.) Java Technology for producing dynamic server responses Servlet Container Client HTTP request Client readable response Web Server Invokes Servlet Gives response Servlet Servlet Other Services Servlet 4

5 JAVA SERVLET (CONT.) 5

6 JAVA SERVLET (CONT.) 6

7 WEB/APPLICATION SERVERS Apache Tomcat GlassFish Server WildFly WebLogic WebSphere 7

8 SERVLET VS. APPLICATION Servlets do not have a main() Entry point to servlet code is via call to a method (e.g. doget()) Servlet interaction with end user is indirect via request/response object APIs Primary servlet output is typically HTML 8

9 SERVLET LIFE CYCLE Controlled by the container The container performs the following steps: 1. If an instance of the servlet does not exist, the web container a) Loads the servlet class. b) Creates an instance of the servlet class. c) Initializes the servlet instance by calling the init method 2. Invokes the service method, passing request and response objects. 3. If it needs to remove the servlet, the container finalizes the servlet by calling the servlet s destroy method. 9

10 WEB APPLICATION LIFECYCLE The process for creating, deploying, and executing a web application can be summarized as follows: 1. Develop the web component code. 2. Develop the web application deployment descriptor, if necessary. 3. Compile the web application components and helper classes referenced by the components. 4. Optionally, package the application into a deployable unit. 5. Deploy the application into a web container. 6. Access a URL that references the web application. 10

11 SERVLET API Contained in two packages javax.servlet javax.servlet.http javax.servlet.genericservlet javax.servlet.http.httpservlet 11

12 WRITING SERVLET PROGRAM Creating and Initializing a Servlet Use annotation contains metadata about the servlet specify at least one URL pattern Extend javax.servlet.http.httpservlet public class HelloServlet extends HttpServlet { 12

13 WRITING SERVLET PROGRAM (CONT.) Override service method The term service method is used for any method in a servlet class that provides a service to a client. The service method of a GenericServlet object The domethod methods of an HttpServlet object or in any other protocol-specific methods 13

14 WRITING SERVLET PROGRAM (CONT.) The general pattern for a service method to extract information from the request, access external resources, and then populate the response, based on that information. public void doget(httpservletrequest request, HttpServletResponse response) 14

15 WRITING SERVLET PROGRAM (CONT.) Getting Information from Requests ServletRequest interface defines methods for accessing the following information: Parameters: to convey information between clients and servlets Object-valued attributes: for communication between the web container and a servlet or between collaborating servlets Information about the protocol: used to communicate the request and about the client and server involved in the request Information relevant to localization 15

16 WRITING SERVLET PROGRAM (CONT.) HttpServletRequest request-path Context path Servlet path Path info query-string Parameters Values 16

17 WRITING SERVLET PROGRAM (CONT.) ServletResponse interface Retrieve an output stream to use to send data to the client To send character data, use the PrintWriter returned by the response's getwriter method. To send binary data in a Multipurpose Internet Mail Extensions (MIME) body response, use the ServletOutputStream returned by getoutputstream. To mix binary and text data, as in a multipart response, use a ServletOutputStream and manage the character sections manually. Indicate the content type (for example, text/html) setcontenttype(string) HTTP response objects: javax.servlet.http.httpservletresponse 17

18 package servlet; import java.io.*; import javax.servlet.*; import javax.servlet.annotation.webservlet; import public class HelloServlet extends HttpServlet { public void doget(httpservletrequest request, HttpServletResponse response) throws ServletException, IOException { response.setcontenttype("text/html"); PrintWriter out = response.getwriter(); out.print("<html>"); out.print("<body>"); out.print("<h2>hello World!</h2>"); out.print("</body>"); } } out.print("</html>"); 18

19 SUMMARY Is a server-side program Needs Web server for execution Communication through Requests/Response javax.servlet and javax.servlet.http packages 19

20 REFERENCES 20

21 THANK YOU 21