6. Why Build Web Pages Dynamically?
The Web page is based on data submitted by the
user
E.g., results page from search engines
The Web page is derived from data that changes
frequently
E.g., a weather report or news headlines page
The Web page uses information from databases or
other server-side sources
E.g., an e-commerce site could use a servlet to build a
Web page that lists the current price and availability of each
item that is for sale.
7.
8. HTTP Request HTTP Response
Key elements of a “request” Key elements of a “response”
stream: stream:
HTTP method (action to be A status code (for whether
performed). the request was successful).
The page to access (a URL). Content-type (text, picture,
html, etc…).
Form parameters.
The content ( the actual
content).
9. Introduction – What is a Servlet
• Where does Servlet come into the picture?
I can serve only
static HTML
pages
Web Server
Application
Dude ,Not a
problem. I
can handle
dynamic
Helper requests.
Application
Web Server machine
“The Helper Application is nothing but a SERVLET”
10. What is java servlet ?
A servlet is a small Java program that runs within a Web server. Servlets
receive and respond to requests from Web clients, usually across HTTP,
the HyperText Transfer Protocol. Servlet is an opposite of applet as a
server-side applet. Applet is an application running on client while servlet
is running on server.
Request
Servlet
Client Response Server
11. Example use of servlet
Processing data POST over HTTPs using HTML form as purchase
order or credit card data
Allowing collaborative between people such as on-line
conferencing
Application/Browser Web Server Database/ FileSystem
(User Interface) (Application Logic) (Persistent Storage)
12. Why Use Servlets ?
One of the reasons that Java became
popular is Applets.
– but there are problems with Applets
• Browser compatibility
Server-side Java
– the code is executed on the server side not the client
side
– a dynamically loaded module that services requests
from a Web server
13. Servlets (contd.)
– vs. Common Gateway Interface (CGI)
• create new process for each request
– most platform independent CGI language - Perl
• start a new instance of interpreter for every request
• CGI runs in a completely separate process from the Web
server
– vs. Server-Side JavaScript
• only available on certain web servers
– vs. Active Server Pages (ASP)
• only available on certain web servers
14.
15. Servlet Architecture -Web Container
• What is a Web Container?
request
GET.
GET. GET.
….. ….. …..
Web Web Servlet
Server Container
Client
16. Servlet Architecture – Web Container
• How does the Container handle a request?
request Servlet
Http request Web
Container <Html>
<Body>
response …….
</Body>
Thread </Html>
Web
Server
response Service()
Client
doGet()
17. Servlet Architecture – Web Container
The CONTAINER
• What is the role of Web Container ?
S2
• Communication Support S1
• Lifecycle Management
JSP1
Multi-threading support
S3
• Security
S4
• JSP Support
The container can contain multiple Servlets & JSPs within it
18. Example for Servers: Netscape Web servers
Microsoft's Internet Information Server (IIS),
the World Wide Web Consortium's Jigsaw Web server
19. Developer(s) Apache Software Foundation
Stable release 7.0.37
(February 18, 2013;)
Preview release Non [±]
Development status Active
Written in Java
Operating system Cross-platform
Type Servlet container
HTTP web server
License Apache License 2.0
Website tomcat.apache.org/
20. Apache
Apache is a very popular server
Apache is a very popular server
66% of the web sites on the Internet use Apache
66% of the web sites on the Internet use Apache
Apache is:
Apache is:
Full-featured and extensible
Full-featured and extensible
Efficient
Efficient
Robust
Robust
Secure (at least, more secure than other servers)
Secure (at least, current standards other servers)
Up to date with more secure than
Up to date with current standards
Open source
Free source
Open
Why use anything else?
Free
3
3
21. • Before you can program with servlets, you must
download and install the Apache group's
implementation of servlets called Tomcat.
• Install the Tomcat with specific port number(default
is 8080
• If the installation is successful, you get the Tomcat’s
home page
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33. Servlet Lifecycle
• The Servlet lifecycle is simple, there is only one main state –
“Initialized”.
Does not exist
The container calls destroy()
the init() before the init()
servlet can service
When a new request
any client requests.
for that servlet
comes in.
To initialize your
Initialized To determine which
servlet before
HTTP method
handling any client
Service() should be called.
requests.
34. Servlet Lifecycle - Hierarchy
Interface Servlet
•
Abstract class GenericServlet If not overridden, implements init()
method from the ‘Servlet’ interface,
Abstract class HttpServlet If not overridden, implements service()
method.
Concrete class Your Servlet We implement the HTTP methods
here.
36. import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloServlet extends HttpServlet
{
public void doGet(HttpServletRequest request,
HttpServletResponse response)throws
ServletException,IOException
37. Request and Response – GET v/s POST
The HTTP request method determines whether doGet() or
doPost() runs.
GET (doGet()) POST (doPost())
The request contains only the Along with request line
HTTP Request request line and HTTP header. and header it also contains
HTTP body.
Parameter The form elements are passed The form elements are
passing to the server by appending at passed in the body of the
the end of the URL. HTTP request.
Size The parameter data is limited Can send huge amount of
(the limit depends on the data to the server.
container)
Usage Generally used to fetch some Generally used to process
information from the host. the sent data.
38. import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloServlet extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse
response)throws ServletException,IOException
{
response.setContentType("text/html");
39. HttpServletResponse Interface
void setContentType( String type )
Specifies the MIME( Multipurpose Internet Mail
Extensions) type of the response to the browser.
The MIME type helps the browser determine how to
display the data (or possibly what other application to
execute to process the data).
For example, MIME type "text/html" indicates that
the response is an HTML document, so the browser
displays the HTML page.
40. import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloServlet extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse
response)throws ServletException,IOException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
41. ServletOutputStream getOutputStream()
Obtains a byte-based output stream enabling binary data to be sent
to the client.
PrintWriter getWriter()
Obtains a character-based output stream enabling text data to be
sent to the client.
42. import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloServlet extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse
response)throws ServletException,IOException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html><head><title>Hello World</title></head>");
out.println("<body><h1>Hello World</h1></body></html>");
}
}
43.
44.
45.
46.
47.
48.
49.
50. Servlet Architecture – Deployment Descriptor
How does the Container know which Servlet the client has
requested for?
A Servlet can have 3 names
<web-app>
………
Client known URL name <servlet>
<servlet-name>Hello</servlet-name>
<servlet-class>HelloServlet</servlet-class>
Deployer known secret </servlet>
internal name
<servlet-mapping>
<servlet-name>Hello</servlet-name>
Actual file name <url-pattern>/HelloNova</url-pattern>
</servlet-mapping>
………..
………..
</web-app>
Web.xml
