The Servlet Technology
Inside Servlets
Writing Servlet Applications
What Is a Servlet?
“A servlet is a server-side Java replacement for CGI
scripts and programs. Servlets are much faster and...
Ways to use Servlet
A simple way:
Servlet can process data which was POSTed
over HTTPS using an HTML FORM, say, an
order-e...
A simple servlet
Some other uses:
Since servlets handle multiple requests concurrently, the
requests can be synchronized with each other to...
Server-side Java for the web
a servlet is a Java program which outputs an html page; it is a
server-side technology
HTTP R...
Servlet Structure
Java Servlet Objects on Server Side
Managed by Servlet Container
Loads/unloads servlets
Directs requests...
A servlet Is a Server-side Java Class
Which Responds to Requests

doGet()

doPost()
service()
doPut()

doDelete()

8
Servlet Basics
Packages:
javax.servlet, javax.servlet.http
Runs in servlet container such as Tomcat
Tomcat 4.x for Servlet...
Web App with Servlets

GET …

Servlet

HEADERS
BODY

doGet()
…
…

Servlet Container
Life-cycle of a servlet
init()
service()
destroy()
It can sit there simply servicing requests with no
start up overhead, n...
Client - Server - DB
5 Simple Steps for Java Servlets
1. Subclass off HttpServlet
2. Override doGet(....) method
3. HttpServletRequest
getParam...
HTTP: Request &
Response
Client sends HTTP request (method) telling
server the type of action it wants performed
GET metho...
Http: Get & Post

GET method
For getting information from server
Can include query string, sequence with additional
inform...
Http: Get & Post

POST method
designed to give information to server
all information (unlimited length) passed as part of
...
Interaction with Client
HttpServletRequest
String getParameter(String)
Enumeration getParameters(String[])

HttpServletRes...
HttpServlet
Implements Servlet
Receives requests and sends responses to a web
browser
Methods to handle different types of...
HttpServlet Request Handling

19
Handling HttpServlet
Requests
service() method not usually overridden
doXXX() methods handle the different request types
N...
Simple Counter Example
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SimpleCounter e...
Multithreading solutions
Synchronize the doGet() method
public synchronized void doGet(HttpServletRequest req,
HttpServlet...
Forms and Interaction
<form method=get action=“/servlet/MyServlet”>
GET method appends parameters to action URL:
/servlet/...
Assignment 2:
Get Stock Price
RequestHeaderExample.java
import
import
import
import

java.io.*;
java.util.*;
javax.servlet.*;
javax.servlet.http.*;

pub...
Accessing Request Components
getParameter("param1")
getCookies() => Cookie[]
getContentLength()
getContentType()
getHeader...
Environment Variables
JavaServlets do not require you to use the
clunky environment variables used in CGI
Individual funct...
Setting Response Components
Set status first!
setStatus(int)

HttpServletResponse.SC_OK...
sendError(int, String)
sendRedi...
Setting Response Components
Set headers
setHeader(…)
setContentType(“text/html”)

Output body
PrintWriter out = response.g...
 Install Web Server on your machine such as Tomcat, Appache, ..
 Create Home Page as CV which should contains:
 Your Na...
Lecture 2
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Lecture 2

  1. 1. The Servlet Technology Inside Servlets Writing Servlet Applications
  2. 2. What Is a Servlet? “A servlet is a server-side Java replacement for CGI scripts and programs. Servlets are much faster and more efficient than CGI and they let you unleash the full power of Java on your web server, including back-end connections to databases and object repositories through JDBC, RMI, and CORBA” – Atlanta Java Users Group (http://www.ajug.org/meetings/jun98.html) 2
  3. 3. Ways to use Servlet A simple way: Servlet can process data which was POSTed over HTTPS using an HTML FORM, say, an order-entry, and applying the business logic used to update a company's order database.
  4. 4. A simple servlet
  5. 5. Some other uses: Since servlets handle multiple requests concurrently, the requests can be synchronized with each other to support collaborative applications such as on-line conferencing. One could define a community of active agents, which share work among each other. The code for each agent would be loaded as a servlet, and the agents would pass data to each other. One servlet could forward requests other servers. This technique can balance load among several servers which mirror the same content.
  6. 6. Server-side Java for the web a servlet is a Java program which outputs an html page; it is a server-side technology HTTP Request HTTP Response browser Server-side Request Response Header + Html file web server Java Servlet Java Server Page servlet container (engine) - Tomcat
  7. 7. Servlet Structure Java Servlet Objects on Server Side Managed by Servlet Container Loads/unloads servlets Directs requests to servlets Request → doGet() Each request is run as its own thread
  8. 8. A servlet Is a Server-side Java Class Which Responds to Requests doGet() doPost() service() doPut() doDelete() 8
  9. 9. Servlet Basics Packages: javax.servlet, javax.servlet.http Runs in servlet container such as Tomcat Tomcat 4.x for Servlet 2.3 API Tomcat 5.x for Servlet 2.4 API Servlet lifecycle Persistent (remains in memory between requests) Startup overhead occurrs only once init() method runs at first request service() method for each request destroy() method when server shuts down
  10. 10. Web App with Servlets GET … Servlet HEADERS BODY doGet() … … Servlet Container
  11. 11. Life-cycle of a servlet init() service() destroy() It can sit there simply servicing requests with no start up overhead, no code compilation. It is FAST It may be stateless – minimal memory 11
  12. 12. Client - Server - DB
  13. 13. 5 Simple Steps for Java Servlets 1. Subclass off HttpServlet 2. Override doGet(....) method 3. HttpServletRequest getParameter("paramName") 4. HttpServletResponse set Content Type get PrintWriter send text to client via PrintWriter 5. Don't use instance variables
  14. 14. HTTP: Request & Response Client sends HTTP request (method) telling server the type of action it wants performed GET method POST method Server sends response 14
  15. 15. Http: Get & Post GET method For getting information from server Can include query string, sequence with additional information for GET, appended to URL e.g. Http://www.whoami.Com/Servlet/search?Name=Inigo&ID=1223344 15
  16. 16. Http: Get & Post POST method designed to give information to server all information (unlimited length) passed as part of request body • invisible to user • cannot be reloaded (by design) 16
  17. 17. Interaction with Client HttpServletRequest String getParameter(String) Enumeration getParameters(String[]) HttpServletResponse Writer getWriter() ServletOutputStream getOutputStream() Handling GET and POST Requests
  18. 18. HttpServlet Implements Servlet Receives requests and sends responses to a web browser Methods to handle different types of HTTP requests: handles GET requests doPost() handles POST requests doPut() handles PUT requests doDelete() handles DELETE requests doGet() 10/12/11 G53ELC: Servlets 18
  19. 19. HttpServlet Request Handling 19
  20. 20. Handling HttpServlet Requests service() method not usually overridden doXXX() methods handle the different request types Needs to be thread-safe or must run on a STM (SingleThreadModel) Servlet Engine multiple requests can be handled at the same time 20
  21. 21. Simple Counter Example import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class SimpleCounter extends HttpServlet { int count = 0; public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType(“text/plain”); PrintWriter out = res.getWriter(); count++; out.println(“This servlet has been accessed “ + count + “ times since loading”); } } 21
  22. 22. Multithreading solutions Synchronize the doGet() method public synchronized void doGet(HttpServletRequest req, HttpServletResponse res) servlet can’t handle more than one GET request at a time Synchronize the critical section PrintWriter out = res.getWriter(); synchronized(this) { count++; out.println(“This servlet has been accessed “ + count + “ times since loading”); } 22
  23. 23. Forms and Interaction <form method=get action=“/servlet/MyServlet”> GET method appends parameters to action URL: /servlet/MyServlet?userid=Jeff&pass=1234 This is called a query string (starting with ?) Username: <input type=text name=“userid” size=20> Password: <input type=password name=“pass” size=20> <input type=submit value=“Login”>
  24. 24. Assignment 2: Get Stock Price
  25. 25. RequestHeaderExample.java import import import import java.io.*; java.util.*; javax.servlet.*; javax.servlet.http.*; public class RequestHeaderExample extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); Enumeration e = request.getHeaderNames(); while (e.hasMoreElements()) { String name = (String)e.nextElement(); String value = request.getHeader(headerName); out.println(name + “ = “ + value ); } } }
  26. 26. Accessing Request Components getParameter("param1") getCookies() => Cookie[] getContentLength() getContentType() getHeaderNames() getMethod()
  27. 27. Environment Variables JavaServlets do not require you to use the clunky environment variables used in CGI Individual functions: PATH_INFO REMOTE_HOST QUERY_STRING … req.getPathInfo() req.getRemoteHost() req.getQueryString()
  28. 28. Setting Response Components Set status first! setStatus(int) HttpServletResponse.SC_OK... sendError(int, String) sendRedirect(String url)
  29. 29. Setting Response Components Set headers setHeader(…) setContentType(“text/html”) Output body PrintWriter out = response.getWriter(); out.println("<HTML><HEAD>...")
  30. 30.  Install Web Server on your machine such as Tomcat, Appache, ..  Create Home Page as CV which should contains:  Your Name as title  You Image in the right hand side  Your previous courses listed in Table  Another linked Page for Accepting your friends which should contains form to accept your friends information:        Name (Text Field) Birth of Date (Text Field) Country ( Drop Down List) E-mail ( Text Field) Mobile ( Text Field) Gender (Radio Button with Male or Female) Save request of friends into file 31

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