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Chapter #2
JAVA SERVLET
PRGRAMMING
@2008 Huynh Ngoc Tin
Objective
 Basic concepts

Why?

What is java servlet?

Servlet container

Servlet life circle

Servlet API, servlet interface

…
 Build, deploy, run a java servlet
@2008 Huynh Ngoc Tin
References
 [1] Chapter 3. Prentice Hall Ptr Java(Tm) Ee 5 Tutorial,
The (3Rd Edition) (The Java Series)
 [2] Marty Hall. Core Servlet and Java Server Page. Sun
Micro System. Prentice Hall PTR; 1 edition 2000.
 [3] http://java.sun.com/products/servlet
@2008 Huynh Ngoc Tin
Basic concepts
 Why?
 What is java servlet?
 What is servlet container?
 Servets on J2EE/JEE Platform
 Servlet Interface
 Servlet Life Circle
 Servlet context
 Request/Response
@2008 Huynh Ngoc Tin
Why?
 The need for dynamic content.

Applets, one of the earliest attempts toward this goal (the
client side)

At the same time, (CGI) scripts were the main technology
used to generate dynamic content

Limitation: Lack of scalability, Java Servlet technology
was created as a portable way to provide dynamic, useroriented content.
@2008 Huynh Ngoc Tin
What is java Servlet?
 One of technologies of J2EE/JEE Platform.
 Java Servlet is Java component that runs on web container.
 Java Servlets “talks” to Web client base on request/ response
that is managed by Servlet Container.
@2008 Huynh Ngoc Tin
What is servlet container (Web container)?
 A Web container is essentially the component of a Web server
that interacts with the servlet.
 The Web container is responsible for managing the life cycle of
servlets
 Mapping a URL to a particular servlet and ensuring that the URL
requester has the correct access rights.
@2008 Huynh Ngoc Tin
What is servlet container (Web container)?
@2008 Huynh Ngoc Tin
Java Servlet on JEE Platform
@2008 Huynh Ngoc Tin
Servlet API
 The javax.servlet and javax.servlet.http packages provide
interfaces and classes for writing servlets.
 The Java Servlet API allows a software developer to add
dynamic content to a Web server using the Java platform. The
generated content is commonly HTML, but may be other data
such as XML.
 The HttpServlet class provides methods, such as doGet and
doPost, for handling HTTP-specific services.
@2008 Huynh Ngoc Tin
Servlet API history
Packages: javax.servlet & javax.servlet.http
@2008 Huynh Ngoc Tin
Servlet Interface
@2008 Huynh Ngoc Tin
Servlet Interface
 Contains methods which are implemented by your servlets
 Define methods to:

Init a java servlet.

Handle requests from the client side.

Remove servlet from the server.
 Your Servlets can implements Servlet Interface or extends from
a other class that implemented Servlet Interface such as
GenericServlet & HttpServlet.
@2008 Huynh Ngoc Tin
Servlet Interface
 public abstract class GenericServlet
extends Object implements Servlet,
ServletConfig, Serializable
 public abstract class HttpServlet
extends GenericServlet implements Serializable
 GenericServlet định nghĩa 1 servlet độc lập
protocol, để định nghĩa 1 servlet dùng trên
Web ta có thể cho kế thừa lớp HttpServlet.
@2008 Huynh Ngoc Tin
Servlet Interface
 Handle request


service method: servlet Interface define service
method to handle requests from the client side.
Servlet Container will call service method to
handle the request from the client side.
@2008 Huynh Ngoc Tin
Servlet Interface
 HttpRequest methods
•
•
HttpServlet have some more methods to handle
HttpRequest:
 doGet for handling HTTP GET requests
 doPost for handling HTTP POST requests
 …
The above methods can are called automatically by service
method
@2008 Huynh Ngoc Tin
Servlet life circle
 Servlet container have only one instance for each servlet.
 Instance is handle by init, service, destroy in Servlet
Interface (JEE API).
 Servlet Container load and init servlets.
 Servlet Container have init servlets before the request come
from the client.
 Servlet Container have to choose a servlet for the request and
make decision what servlet will be removed from the server.
@2008 Huynh Ngoc Tin
Request & Reponse
@2008 Huynh Ngoc Tin
Request & Reponse
 Request



Package all information that comes from the client.
Request from Client -> Server follows the HTTP protocol
HttpServletRequest methods can summarize, read the
request’s information.
@2008 Huynh Ngoc Tin
Request & Response
 Response



Package all information that will response for the client.
Information in response object are sent to client by HTTT
protocol
HttpServletReponse methods can summarize, package
information into response object.
@2008 Huynh Ngoc Tin
Request & Response
 Hypertext Transfer Protocol reference to:
 http://djce.org.uk/dumprequest
 http://www.w3.org/Protocols/rfc2616/rfc2616.html
 http://www.faqs.org/rfcs/rfc2616.html
Example – Login Servlet




 Step by step
Define a class name LoginServlet extends from GenericServlet
or HttpServlet class
Implement/override the following methods
 init()
 service()
 destroy()
Compile and deploy on webserver.
Call to run by URL from the client side
@2008 Huynh Ngoc Tin
Example – Login Servlet
import javax.servlet.http.*;
import java.io.*;
import java.sql.*;
public class LoginServlet extends HttpServlet {
public void service(HttpServletRequest request,
HttpServletResponse response) throws IOException {
// ….
}
}
@2008 Huynh Ngoc Tin
Example – Login Servlet
// inside the service method
…
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
String
strUsername
= request.getParameter("Username");
String
strPassword
= request.getParameter("Password");
…
@2008 Huynh Ngoc Tin
Example – Login Servlet
Deploy the servlet on Apache Tomcat Web Server
 Web Server Apache Tomcat (read the document of other web
servers to know how to deploy a servlet)
 Step 1: Copy servlet file class into WEB-INF\classes of
your web application.
 Step 2:
 Add information about your servlet into web.xml file to
notify with the web server or application server.
 WEB-INF\web.xml
@2008 Huynh Ngoc Tin
Example – Login Servlet
web.xml file (configuration)
<web-app>
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/servlets/LoginServlet</url-pattern>
</servlet-mapping>
</web-app>
@2008 Huynh Ngoc Tin
Example – Login Servlet
• Call a servlet from client side
•
Call a servlet when user clicks submit or login button from the
LoginForm/client side
…
• <Form action="../../servlets/LoginServlet"
method="post">
• …
•
@2008 Huynh Ngoc Tin
Connecting to Database
 Directly
 Using the connection pool
Connecting to Database
Connecting to Database
Connecting to Database
Connecting to Database
Connecting to Database
Deploy a web app on Tomcat webserver
@2008 Huynh Ngoc Tin
Exercises
 Study by yourself client side programming such as HTML, Java
Script.
 Build, deploy and run servlets which do the below functions
using NetBean 6.1 (include JBoss, GlassFish Application Server)
 Registration (RegisterServlet)
 Login (LoginServlet)
 Change password, registered information
(UpdateUserInformationServlet)
 Read more about JBoss, GlassFish, Tomcat document to deploy
a java servlet
@2008 Huynh Ngoc Tin