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XML Technology in E-Commerce
Lecture 4
Case Study: XmlMessenger
XML Technology in E-Commerce 2001
Lecture 4
Sheet 1
Lecture Outline
• Instant Messaging;
• Case Study: XMLMessenger
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Communication between client and server;
Application classes;
Sending and receiving XML through network;
User login;
Sending and receiving messages;
• Summary;
XML Technology in E-Commerce 2001
Lecture 4
Sheet 2
Overview
XML Technologies and Applications
XML Docs
Logical Structure
Physical Structure
DTD
XML Schema
Meta-Modeling
XML Parser
Well-formedness
Validity
SAX
DOM
Applications
E-Commerce
XML Technology in E-Commerce 2001
Lecture 4
Sheet 3
Instant Messaging
An E-Commerce Application
• One of the most popular communication services;
• 175 million users are expected by 2002;
• Deployment on new client types is expected:
mobiles, PDAs, TVs;
• Vendors:
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AOL;
Yahoo;
Infoseek;
ICQ;
XML Technology in E-Commerce 2001
Lecture 4
Sheet 4
Case Study
XMLMessenger
• Simple Client/Server E-Commerce application;
• Demonstrates some of XML capabilities utilized
by the current eCommerce systems:
– Platform and language independent data
representation;
– Standardized data exchange between involved
parties;
– Communication protocol implementation;
XML Technology in E-Commerce 2001
Lecture 4
Sheet 5
XML Messenger
User 4
User 3
Messenger
Server
User 2
User 1
XML Technology in E-Commerce 2001
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Sheet 6
XML Messenger
Login
<users>
<user>User 2</user>
<user>User 3</user>
</users>
User 3
<update type=“login”>
<user>User 1</user>
</update>
<user>User 1</user>
<nameInUse/>
User 1
XML Technology in E-Commerce 2001
<users>
<user>User 2</user>
<user>User 3</user>
</users>
Lecture 4
User 2
Sheet 7
XML Messenger
Messages
<message to=“User 2”
from=“User 1”>
Hello!
</message>
User 3
<message to=“User 2”
from=“User 1”>
Hello!
</message>
Messenger
Server
User 1
User 2
XML Technology in E-Commerce 2001
Lecture 4
Sheet 8
XML Messenger
Logout
<update type=“logout”>
<user>User 1</user>
</update>
User 3
<update type=“logout”>
<user>User 1</user>
</update>
<disconnect/>
Messenger
Server
User 1
User 2
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Sheet 9
XML Messenger
Class Diagram
XML Technology in E-Commerce 2001
Lecture 4
Sheet 10
Class Responsibilities
• MessengerServer:
– Listens for new client connections;
– Maintains an in-memory XML document with online
users;
– Manages a set of threads (one thread per client);
• UserThread:
– Communicates with a particular client;
• MessengerClient:
– Communicates with the corresponding thread on the
server;
– Manages client-side GUI;
XML Technology in E-Commerce 2001
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Sheet 11
Class Responsibilities
• ClientStatus:
– Displays a list of online users;
– Manages conversations with other users;
• Conversation:
– Displays the messages exchanged with a particular
user;
– Provides interface for entering a new message;
XML Technology in E-Commerce 2001
Lecture 4
Sheet 12
XML Messenger
Demo
• Demo - Deitel 10, page 263;
• Tools:
– Java 1.2.2;
– Java API for XML Processing (JAXP) 1.0.1;
• Classes: jaxp.jar and parser.jar;
• Demo files:
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MessengerServer.java
UserThread.java
MessengerClient.java
ClientStatus.java;
Conversation.java
XML Technology in E-Commerce 2001
Lecture 4
Sheet 13
Implementation
Sending XML through network
OutputStream output;
Document message;
try {
((XmlDocument)message).write(output);
}
catch (IOException e){
e.printStackTrace();
}
This fragment is used in:
• MessengerClient, method send;
• UserThread, method send;
XML Technology in E-Commerce 2001
Lecture 4
Sheet 14
Implementation
Receiving XML from network
InputStream input;
int bufferSize = 0;
bufferSize = input.available();
if (bufferSize > 0) {
byte buf[] = new byte[bufferSize];
input.read(buf);
InputSource source = new InputSource(
new ByteArrayInputStream(buf));
Document message = builder.parse(source);
if (message != null)
messageReceived(message);}
This fragment is used in UserThread.run and
MessengerClient.runMessengerClient.
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Sheet 15
Implementation
User Login
XML Technology in E-Commerce 2001
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Sheet 16
Implementation
User Login
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Sheet 17
User Login
• Login message creation (MessengerClient.java):
factory=DocumentBuilderFactory.newInstance();
builder=factory.newDocumentBuilder();
………
public void loginUser(){
Document submitName = builder.newDocument();
Element root = submitName.createElement("user");
submitName.appendChild(root);
root.appendChild(
submitName.createTextNode(name.getText()));
send(submitName);
}
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Sheet 18
User Login
• Getting output and input streams (MessengerClient.java):
public void runMessengerClient(){
….………………………..
output = clientSocket.getOutputStream();
input = clientSocket.getInputStream();}
• Sending an XML message through the network (method
send):
try {
((XmlDocument)message).write(output);
}
catch (IOException e) {
e.printStackTrace();}
XML Technology in E-Commerce 2001
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Sheet 19
User Login
• Reading the XML message from the network stream
(UserThread.java)
public void run(){
……………………………………………..
int bufferSize = 0;
bufferSize = input.available();
if ( bufferSize > 0 ) {
byte buf[] = new byte[bufferSize];
input.read(buf);
InputSource source = new InputSource(
new ByteArrayInputStream(buf));
Document message = builder.parse(source);
if ( message != null )
messageReceived(message);
Class InputSource in package org.xml.sax
XML Technology in E-Commerce 2001
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Sheet 20
User Login
• Analyzing the message (UserThread.java):
public void messageReceived(Document message){
Element root = message.getDocumentElement();
if (root.getTagName().equals("user")) {
String enteredName=
root.getFirstChild().getNodeValue();
if (server.findUserIndex(enteredName)!= -1)
nameInUse();
else {
send(server.getUsers());
username = enteredName;
server.addUser(this);
}
}
………………………………………………………………….
XML Technology in E-Commerce 2001
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Sheet 21
User Login
• Initialization of the document with user names
(MessengerServer.java):
private Document initUsers()
{
Document init = builder.newDocument();
init.appendChild(init.createElement("users"));
return init;
}
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Sheet 22
User Login
• Adding new user (MessengerServer.java):
public void addUser(UserThread newUserThread){
String userName = newUserThread.getUsername();
updateGUI( "Received new user: " + userName );
// notify all users of user's login
updateUsers( userName, "login" );
// add new user element to Document users
Element usersRoot = users.getDocumentElement();
Element newUser = users.createElement( "user" );
newUser.appendChild(
users.createTextNode( userName ) );
usersRoot.appendChild( newUser );
updateGUI( "Added user: " + userName );
// add to Vector onlineUsers
onlineUsers.addElement( newUserThread );}
XML Technology in E-Commerce 2001
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Sheet 23
User Login
• Notification for new user login (MessengerServer.java):
public void updateUsers(String userName,
String type){
Document doc = builder.newDocument();
Element root = doc.createElement( "update" );
Element userElt = doc.createElement( "user" );
doc.appendChild( root );
root.setAttribute( "type", type );
root.appendChild( userElt );
userElt.appendChild(doc.createTextNode(userName));
// send to all users
for (int i = 0; i < onlineUsers.size(); i++){
UserThread receiver =
(UserThread)onlineUsers.elementAt( i );
receiver.send( doc );}
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Sheet 24
Message Sending
XML Technology in E-Commerce 2001
Lecture 4
Sheet 25
Message Sending
XML Technology in E-Commerce 2001
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Sheet 26
Message Sending
• Construction of a message in the conversation window
(Conversation.java):
public void submitMessage(){
……………………
Document sendMessage;
……………………
sendMessage = builder.newDocument();
Element root = sendMessage.createElement("message");
root.setAttribute( "to", target );
root.setAttribute( "from", clientStatus.getUser() );
root.appendChild(
sendMessage.createTextNode( messageToSend ));
sendMessage.appendChild( root );
client.send( sendMessage );
………………………………
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Sheet 27
Message Sending
• Message handling in MessengerServer:
public void sendMessage(Document message){
Element root = message.getDocumentElement();
String from = root.getAttribute("from");
String to = root.getAttribute("to");
int index = findUserIndex(to);
………………………………………
UserThread receiver =
(UserThread) onlineUsers.elementAt(index);
receiver.send(message);
………………………………………
}
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Sheet 28
Message Sending
• Message handling on the recipient side
(MessengerClient.java):
public void messageReceived(Document message){
Element root = message.getDocumentElement();
………………………
if(root.getTagName().equals("message")){
String from = root.getAttribute( "from" );
String messageText =
root.getFirstChild().getNodeValue();
……………………
int index = findConversationIndex( from );
……………………
Conversation receiver =
(Conversation) conversations.elementAt(index);
receiver.updateGUI(from+": "+messageText);
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Sheet 29
Summary
• Demonstration of XML technology for a simple ECommerce application;
• Implementation of a communication protocol with XML
messages;
• Handling of in-memory XML documents through DOM
calls;
• Sending and receiving XML through network connection;
Read: Deitel 10;
Assignment:
• Modify the login message to include information about login time.
Update the user interface accordingly;
• DeitelEx 10.4
For more detailed explanation and some hints see the course site.
XML Technology in E-Commerce 2001
Lecture 4
Sheet 30