Download 4020-Lecture3_4 - eee

ITEC 4020A:Internet Client Server Systems
Professor: Marin Litoiu
Lectures 3&4: Internet Protocols
© Marin Litoiu, York University, Canada
This lecture uses captions from “Distributed Systems: Concepts and Design, 4/E, by
Dean Dollimore, Tim Kindberg, George Coulouris
Content
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Networks
HTTP protocols
Servlets
JSP
Model View Controller
Summary
© Marin Litoiu, York University, Canada
Networks
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Networks: transmission media ( wire, cable,
fibre, wireless), hardware devices( interfaces,
routers) and software ( drivers, protocols)
Latency: the time from when the data leaves the
computer till it reaches the destination
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In most media, the bits go with the sped of light
On the fastest link between Europe and Australia, the
latency is 0.13s
Latency=distance/(speed of the data)
Data transfer rate(bandwidth): bits
send/received per second
Message transmission
time=latency+length/(data transfer rate)
Q: how long takes to transfer 2MB data between
two computers located at 7000Km of each
other? Assume a transmission rate of 20KB/s
and that data travels with the speed of light
A:T=(7000/300000)+ 2000/20= 100.0233
seconds
Applications, services
(Your project, for example)
Applications
Middleware
(RPC, CORBA, RMI, DCOM, Web Services)
Network software(TCP/IP)
Operating system
(Windows, Linux, Mac OS)
Platform
Computer and network hardware
© Marin Litoiu, York University, Canada
Networks and their performance: bandwidth and
latency
Example
Range
Bandwidth
(Mbps)
Latency
(ms)
LAN
Ethernet
1-2 kms
10-1000
1-10
WAN
IP routing
worldwide
0.010-600
100-500
MAN
ATM
250 kms
1-150
10
Internetwork
Internet
worldwide
0.5-600
100-500
WPAN
Bluetooth (802.15.1)
10 - 30m
0.5-2
5-20
WLAN
WiFi (IEEE 802.11)
0.15-1.5 km
2-54
5-20
WMAN
WiMAX (802.16)
550 km
1.5-20
5-20
WWAN
GSM, 3G phone nets
worldwide
0.01-02
100-500
Wired:
Wireless:
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Routing in a wide area network affects latency and
bandwidth
message
connection
A
Hosts
or local
networks
1
B
2
3
Links
4
C
5
D
6
E
Routers
© Marin Litoiu, York University, Canada
Protocol layers in the ISO Open Systems
Interconnection (OSI) model
Mess age receiv ed
Mess age s ent
Lay ers
Applic ation
Pres entat ion
Sess ion
Transport
Netw ork
Data link
Phy sical
Sender
Communic at ion
medium
© Marin Litoiu, York University, Canada
Recipient
OSI protocol summary
Layer
Description
Examples
Application
Protocols that are designed to meet the communication requirements of
specific applications, often defining the interface to a service.
Presentation
Protocols at this level transmit data in a network representation that is
independent of the representations used in individual computers, which may
differ. Encryption is also performed in this layer, if required.
At this level reliability and adaptation are performed, such as detection of
failures and automatic recovery.
This is the lowest level at which messages (rather than packets) are handled.
Messages are addressed to communication ports attached to processes,
Protocols in this layer may be connection-oriented or connectionless.
Transfers data packets between computers in a specific network. In a WAN
or an internetwork this involves the generation of a route passing through
routers. In a single LAN no routing is required.
Responsible for transmission of packets between nodes that are directly
connected by a physical link. In a WAN transmission is between pairs of
routers or between routers and hosts. In a LAN it is between any pair of hosts.
The circuits and hardware that drive the network. It transmits sequences of
binary data by analogue signalling, using amplitude or frequency modulation
of electrical signals (on cable circuits), light signals (on fibre optic circuits)
or other electromagnetic signals (on radio and microwave circuits).
HTTP, FTP , SMTP,
CORBA IIOP
Secure Sockets
(SSL),
Session
Transport
Network
Data link
Physical
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TCP, UDP
IP, ATM virtual
circuits
Ethernet MAC,
ATM cell transfer,
PPP
Ethernet base- band
signalling,
ISDN
TCP/IP layers
Layers
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Application
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Message
 A “channel is established between
source and destination
 The source checks that each packet is
delivered to destination
 Eventually retransmits the packets
 The protocol is reliable, it guarantees
transmission
Messages (UDP) or Streams (TCP)
Transport
UDP or TCP packets
Internet

IP datagrams
UDP: user datagram protocol
 Each packet might have its own route
 The sender does not check if each
packet arrived at destination
 The protocol is not reliable
Network interface
Network-specific frames
Application protocols: ftp, http, smtp
A message is split in “packets”
Each packet is transmitted
independently
TCP: transport control protocol
 IP: internet protocol
 Adds the IP addresses ( of the source
and destination) to the packet
 Routes the packets to the first router
Underlying network
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IP packet layout
header
IP addres s of s ource
IP addres s of des tination
up to 64 kiloby tes
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data
Client Server programming
Client
Server
Client library
Server library
network
 HTTP
 Servlets and JSP
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HTTP (Hyper Text Transfer Protocol)
 Client sends a message(request); the
server responds with another message(
reply)
 The message includes the method name,
the arguments, the results of the method
and how data is represented
 http 1.0 was connectionless
HTTP
Client(Browser)
HTTP Server(Web
Server)
Request
message
 The server closes its connection, release its
resources after first request
(wait)
 http 1.1 connection oriented
 The server keeps the connection open;
subsequent requests from the same client are
served faster
 The server listen ( usually) on port 80
 The messages are delivered through the
underlying TCP/IP protocol
Reply
Get the message
Select the method
-GET
-PUT
-POST...
Execute the method
Return a result
message
Socket
Any port
TCP
IP
© Marin Litoiu, York University, Canada
Socket
Port 80
HTTP request and reply messages
method
URL or pathname
GET
//www.dcs.qmw.ac.uk/index.html
HTTP version
HTTP/1.1

status code
200
HTTP version
headers message body
HTTP/ 1.1
reason
OK
headers
message body
resource data
Methods
 GET: requests a resource whose URL (locator) follows
 HEAD: Identical to GET, does not return data, but info about the data( size, type, etc..)
 POST: specify the URL of a resource that can process the data ( used for forms, when you send user data to the
server
 PUT: store the data to the URL specified
 DELETE: deletes the resource specified
 TRACE: the server sends back the request message; used for diagnostic
 OPTIONS: the server sends back the methods it supports and its special requirements
© Marin Litoiu, York University, Canada
Writing a Java HTTP Client
import java.net.*;
import java.io.*;
HTTP classes are in
the java.net package
public class HTTPClient {
public static void main(String[] args) throws Exception {
URL york = new
URL("http://www.yorku.ca/mlitoiu/teaching/4020A/ITEC4020A.html");
URLConnection yc = york.openConnection();
To connect to a
server, you open an
URL connection
BufferedReader in = new BufferedReader(
new InputStreamReader(
yc.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null)
System.out.println(inputLine);
in.close();
Then you read from
that connection
}
}
© Marin Litoiu, York University, Canada
Your turn
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What is HTTP programming
Name 4 server Http methods
What do you need to know about the server in order to write a http client?
In http programming, how would one write a server program?
© Marin Litoiu, York University, Canada
Servlet
 Handle HTTP GET and POST methods on server side
 A servlet is a Java class with two main methods:
 doGet and
 doPost
 Functionality
 Handle requests coming from clients
 Possibly generate responses for the clients
 Other methods
 init -- called before handling any request
 getServletInfo
 getServletConfig
 The servlet can be invoked manually (in a browser) or programmatically,
from another program ( see next slides)
 A servlet runs in a web/application server ( Tomcat, Websphere…)
© Marin Litoiu, York University, Canada
doGet and doPost --Method signatures
public class SampleServlet extends javax.servlet.http.HttpServlet implements
javax.servlet.Servlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//add your implementation
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// add your implementation
}
}
 Request- contains the information coming from client
 Response- contains the information going to the client
© Marin Litoiu, York University, Canada
Servlet- An Example
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>Hello 4020 World!</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Hello World!</h1>");
out.println("</body>"); out.println("</html>");
}
}
What does this servlet
do?
How do you invoke this
servlet?
What is the URL of the
servlet?
© Marin Litoiu, York University, Canada
HttpServletRequest
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
//add your implementation
 Input for both doGet and doPost
 Methods:
 String getParameter (String paramName)
 HttpSession getSession (boolean createFlag)
Ex: request.getParameter(“language”)
request.getSession(true)
© Marin Litoiu, York University, Canada
HttpServletRespons
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
//add your implementation
 Input for both doGet and doPost
 Methods:
 PrintWriter getWriter ()
 void setContentType (String contentType)
Ex:response.getWriter()
response.setContentType(”html”)
© Marin Litoiu, York University, Canada
Calling a servlet
 Explicit URL
http://serverName:port/appName/servletName
where servletName can be of form servletClass.class
 Implicit call – using a form’s action attribute
 Get parameters can be sent with the URL
url?param1name=param1value&param2name=param2value&…
© Marin Litoiu, York University, Canada
Session tracking
 Need for session tracking
 HTTP has no session tracking features
 Distinguish between multiple clients
 “remember” information specific to clients
 Can be done with cookies
 Class HttpSession – Java class for session tracking
 Lifetime of an HttpSession object
 Lifetime of other objects (request, response)
© Marin Litoiu, York University, Canada
Additional resources
 Read the “Basics” Chapter of your textbook
 Try the Servlets examples: http://sit.yorku.ca:8080/examples/
 You can view the source and execute the servlet
 It is time to test your server environment, see the link:
 Http://www.yorku.ca/mlitoiu/teaching/Generic_Public_4020/ServerSetup/Server.htm
 It is recommended that you use a development environment:
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Eclipse: for code development
Tomcat : for deployment and testing
MySql: for database
See the “Resources” on the course web site on how to install them on your
computer
© Marin Litoiu, York University, Canada
JSP
 Motivation
 Definition: JSP = HTML + Java
© Marin Litoiu, York University, Canada
Overview
Java components in JSPs:
Directives: define page settings, compilation time
includes, custom tag libraries specification
Actions: functionality encapsulated in predefined tags
(jsp:useBean, jsp:include = call time include)
Scriptlets: Java code
Tag libraries: custom tag extensions
JSP usage:when an HTML page must be
customized
Life cycle: when a JSP is called it is first
translated into a servlet
© Marin Litoiu, York University, Canada
Implicit objects: Scopes
 Scopes
 Application: owned by the servlet container
 Page: objects exist only in the page where they are defined
 Request: exist in the interval between receiving the request by the
container and sending the response (Remark: can have the request
forwarded from resource_1 to resource_2)
 Session: exist during the duration of a session
© Marin Litoiu, York University, Canada
JSP Sample: Hello World
<%@ page language="java" contentType="text/html; charset=ISO8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO8859-1">
<title>Insert title here</title>
</head>
<body>
<p> Hello 4020</p>
</body>
</html>
© Marin Litoiu, York University, Canada
Model View Controller Architecture
Data
base
Java
Beans
© Marin Litoiu, York University, Canada
A MVC Example
 If the user types “french”, he/she is greeted in French, otherwise in
English
MultiLingualServlet.java
Browser
2
3
hello.jsp
4
1
GreetingsJSP.jsp
© Marin Litoiu, York University, Canada
Bonjour.jsp
JSP and forms (The View)
<body>
<p><br>
Greetings</p>
<form ACTION="MultiLingualServlet" METHOD="POST"><b>Language</b>
<input type="text" name="language" size="20"> <br>
<input type="submit" name="Say" value="Say it">
</form>
</body>
The “form” above has
 a button, labelled “Say it”
a text box named “language”
When the button is pressed, a servlet named
MultiLingualServlet is invoked (its method doPost)
© Marin Litoiu, York University, Canada
Servlet (The Controller)
protected void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException,
IOException {
//this parameter comes from the client and is inserted into the request ( see the GreetingsJSP.jsp page)
String greetings=request.getParameter("language");
try {
//based on the value of the parameter “language”, we invoke the Bonjour.jsp, or the Hello.jsp page...
if (greetings.equals("french"))
//this is how you forward the request to another object. Note that you pass the request and response
getServletConfig(). getServletContext().getRequestDispatcher( "/Bonjour.jsp").forward(request, response);
else
getServletConfig().getServletContext().getRequestDispatcher("/Hello.jsp").forward(request, response);
} catch(Exception e) {
e.printStackTrace();
}
}
© Marin Litoiu, York University, Canada
Another View ( Bonjour.jsp)
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Bonjour</title>
</head>
<body>
<p> Bonjour 4020</p>
</body>
</html>
© Marin Litoiu, York University, Canada
Another example: MVC with JSP, Servlets, Beans


Register names, retrieve names
1. shows a form; user inputs first, last names; 2. a servlet is invoked when “submit” is pressed; 3. the servlet retrieves or
creates a Bean, Name, fills in the fields, and then save ssthe bean in the “session” object; 4. the servlet passes the control
to ShowNames.jsp; 5. ShowNames retrieves the bean fields and display she names.
3
UserRegistration.java
Browser
2
1
5
UserReg.jsp
© Marin Litoiu, York University, Canada
4
Name.java
ShowNames.
jsp
UserReg.jsp: filling the forms…
<p><br>
Greetings</p>
<form ACTION="UserRegistration"
METHOD="POST">
<b>First Name</b> <input type="text"
name="firstName" size="20"> <br>
<b>Last Name</b> <input type="text"
name="lastName" size="20"> <br>
<input type="submit" name="submit"
value="Submit"></form>
</body>
</html>
When done (button
“Submit” pressed)
invoke the servlet
“UserRegistration”
Notice the names of the
fields, you need to
remember those when
implement the servlet
UserRegistration..
© Marin Litoiu, York University, Canada
The bean Name: stores the data
package users;
public class Name {
private String firstName="first name missing";
private String lastName="last name missing";
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
A bean is a java object
To set and get the field
X of a bean, you use
setX, getX methods…
Do not initialize the
fields to constructors
}
© Marin Litoiu, York University, Canada
The UserRegistration servlet ( controller)
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
IOException {
// get the session object, by calling a request method
HttpSession session= request.getSession();
//once I have the session, I want to know if the session has an object Name --- named "NameBean"--Name nameBean= (Name)session.getAttribute("NameBean");
if (nameBean==null) {
// if it does not, I need to create an object Name
nameBean=new Name();
}
//now get the attributes that came from client ( see the UserReg.jsp for the form and its text fields... )
String fn= request.getParameter("firstName");
if ((fn!=null)&&(!fn.trim().equals(""))){
nameBean.setFirstName(fn);
}
//get the last name...
String ln= request.getParameter("lastName");
if ((ln!=null)&&(!ln.trim().equals(""))){
nameBean.setLastName(ln);
}
© Marin Litoiu, York University, Canada
….The UserRegistration servlet ( controller)
…….
//store the bean in the session and request objects so other servlets or JSP can use them
( see ShowNames.jsp)
session.setAttribute("NameBean", nameBean);
request.setAttribute("NameBean", nameBean);
//pass the control to a JSP...
getServletConfig(). getServletContext().getRequestDispatcher(
"/ShowNames.jsp").forward(request, response);
}
© Marin Litoiu, York University, Canada
And finally….ShowNames.jsp
</head>
<body>
<jsp:useBean id="NameBean"
type="users.Name"
scope="session"></jsp:useBean>
Retrieves the bean “nameBean” from the
session object
<jsp:getProperty name="NameBean"
property="firstName"/>
Displays the field “firstName” of the bean
<jsp:getProperty name="NameBean"
property="lastName"/>
<p>
</p>
</body>
</html>
Displays the fields “lastName” of the
bean
© Marin Litoiu, York University, Canada
Summary
 Networks
 Network protocols are organized in layers
 TCP, UDP
 IP
 Programming at the network layers are done through sockets
 HTTP
 GET
 POST
 Servlets: user requests are forwarded to doGet and doPost
 Java Server Pages
 HTML+java
 Are compiled to Servlets
 Model View Controller
 JSP- View
 Servlet –Controller
 Java beans( interacting with the database) - Model
© Marin Litoiu, York University, Canada