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Internet Technologies
XML Messaging
A PowerWarning application using servlets and SAX
The PowerWarning Application is from “XML and
Java” by Maruyama, Tamura, and Uramoto, Addison-Wesley.
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XML Messaging Part I
The PowerWarning application allows users to register
their geographical position and their temperature concerns.
Users will receive e-mail when the temperature exceeds the user
specified parameters.
This example is from
“XML and Java” by Maruyama, Tamura, and Uramoto, Addison-Wesley.
The web container is called Jigsaw from the W3C.
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Suppose that we know that the weather information is available
from the web at
http://www.xweather.com/White_Plains_NY_US.html.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
<html>
<head>
<title>Weather Report</title>
</head>
<body>
<h2>Weather Report -- White Plains, NY </h2>
<table border=1>
<tr><td>Date/Time</td><td align=center>11 AM EDT Sat Jul 25
1998</td></tr>
[9]
<tr><td>Current Tem.</td><td align=center>70°</td></tr>
[10]
<tr><td>Today’s High</td><td align=center>82°</td></tr>
[11]
<tr><td>Today’s Low</td><td align=center>62°</td><tr>
[12] </table>
[13] </body>
[14] </html>
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•Strategy 1:
For the current temperature of White Plains, go to line 9,
column 46 of the page and continue until reaching the next
ampersand.
•Strategy 2:
For the current temperature of the White Plains, go to the
first <table> tag, then go to the second <tr> tag within the
table, and then go to the second <tg> tag within the row.
Neither of these seems very appealing…
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<?xml version=“1.0”?>
<!DOCTYPE WeatherReport SYSTEM
“http>//www.xweather.com/WeatherReport.dtd”>
<WeatherReport>
<City>White Plains</City>
XML would help
<State>NY</State>
<Date>Sat Jul 25 1998</Date>
<Time>11 AM EDT</Time>
<CurrTemp unit=“Farenheit”>70</CurrTemp>
<High unit=“Farenheit”>82</High>
<Low unit=“Farenheit”>62</Low>
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</Weather Report>
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•Strategy 3:
For the current temperature of White Plains, N.Y., go
to the <CurrTemp> tag.
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WeatherReport
application
Mobile users
XSLT
WML
HTML
XML
PC users
Http://www.xweather.com
PowerWarning
application
XML
Email notifications
XML
Application
programs
Registrations
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The XML Describing the Weather
<?xml version="1.0" encoding="UTF-8"?>
This file is behind
<WeatherReport>
Jigsaw in the file
<City>Pittsburgh</City>
Www/weather/
<State>PA</State>
weather.xml.
<Date>Wed. April 11, 2001</Date>
<Time>3</Time>
<CurrTemp Unit = "Farenheit">70</CurrTemp>
<High Unit = "Farenheit">82</High>
Perhaps this is
<Low Unit = "Farenheit">62</Low>
being served up
</WeatherReport>
by www.xweather.com
for ½ cents per hit.
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Serving the weather
// This servlet file is stored in Www/Jigsaw/servlet/GetWeather.java
// This servlet returns a user selected xml weather file from
// the Www/weather directory and returns it to the client.
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
This data would not
normally be retrieved
from a file.
public class GetWeather extends HttpServlet {
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public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
String theData = "";
/* For simplicity we get the user’s request from the path. */
String extraPath = req.getPathInfo();
extraPath = extraPath.substring(1);
// read the file
try {
// open file and create a DataInputStream
FileInputStream theFile =
new FileInputStream("c:\\Jigsaw\\Jigsaw\\”+
“Jigsaw\\Www\\weather\\"+extraPath);
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InputStreamReader is = new InputStreamReader(theFile);
BufferedReader br = new BufferedReader(is);
// read the file into the string theData
String thisLine;
while((thisLine = br.readLine()) != null) {
theData += thisLine + "\n";
}
}
catch(Exception e) {
System.err.println("Error " + e);
}
PrintWriter out = res.getWriter();
out.write(theData);
System.out.println("Wrote document to client");
out.close();
}
}
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WeatherReport
application
Mobile users
XSLT
WML
HTML
XML
PC users
Http://www.xweather.com
PowerWarning
application
XML
Email notifications
XML
Application
programs
Registrations
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Registrations (HTML)
<!-- PowerWarningForm.html -->
<html>
<head>
<title>PowerWarning</title>
</head>
<body>
<form method="post" action="/servlet/PowerWarn">
E-Mail
<input type="text" name = "User"> <p>
State
<input type="text" name = "State"> <p>
City
<input type="text" name = "City"> <p>
Temperature
<input type="text" name = "Temperature"> <p>
Duration
<input type="text" name = "Duration"> <p>
<input type = "submit">
</form>
</body>
</html>
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Registrations (Servlet)
The servlet will create a watcher object for each registered
user. The watcher object will be told of each user’s location
and temperature requirements. Each watcher object will run
in its own thread and may or may not notify its assigned
user by email.
On servlet initialization, we will start up an object whose
responsibility it is to periodically wake up and tell the watcher
objects to check the weather.
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Registrations (Servlet)
/* This servlet is called by an HTML form. The form passes
the user email, state, city, temperature and duration.
*/
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class PowerWarn extends HttpServlet {
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static Hashtable userTable;
/* Holds (email,watcher) pairs */
public void init(ServletConfig conf) throws ServletException {
super.init(conf);
PowerWarn.userTable = new Hashtable();
Scheduler scheduler = new Scheduler();
scheduler.start();
/* Run the scheduler */
}
/* The scheduler can see the hash
table. It has package access.
*/
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public void doPost(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
/* Collect data from the HTML form */
String par_user =
String par_state =
String par_city =
int par_temp =
req.getParameter("User");
req.getParameter("State");
req.getParameter("City");
Integer.parseInt(
req.getParameter("Temperature"));
int par_duration = Integer.parseInt(
req.getParameter("Duration"));
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/* Assign a watcher to this user. */
Watcher watcher = new Watcher(par_user, par_state, par_city,
par_temp, par_duration);
/* Place the (email,watcher) pair in the hash table. */
PowerWarn.userTable.put(par_user, watcher);
res.setContentType("text/html");
PrintWriter writer = res.getWriter();
writer.print("<html><head></head><body><b>” +
“You'll be notified by email</b></body></html>");
writer.close();
}
}
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Servlet
Http Request
PowerWarn.userTable
Watcher
[email protected]
Email
User
data
Http Request
Watcher
User
data
[email protected]
Email
Scheduler
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The Scheduler
import java.util.Enumeration;
public class Scheduler extends Thread {
public void run() {
System.out.println("Running scheduler");
while(true) {
Enumeration en = PowerWarn.userTable.elements();
while(en.hasMoreElements()) {
Watcher wa = (Watcher)en.nextElement();
new Thread(wa).start();
}
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try {
/* put this thread to sleep for 15 seconds */
Thread.sleep(1000 * 15);
}
catch(InterruptedException ie) {
// ignore
}
} /* end while */
}
Fifteen seconds for
testing.
public Scheduler() {
super();
}
}
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The Watcher Class
The Watcher objects make HTTP requests to get XML.
How should we handle the XML? SAX or DOM? SAX.
How do we send email? JavaMail.
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import org.xml.sax.*;
import org.xml.sax.helpers.ParserFactory;
import java.io.*;
import java.net.*;
import org.w3c.dom.Document;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
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public class Watcher extends HandlerBase implements Runnable {
String user, state, city;
int temp, duration, overTemp;
public Watcher(String user, String state, String city, int temp,
int duration) {
super();
this.user = user;
this.state = state;
this.city = city;
this.temp = temp;
this.duration = duration;
this.overTemp = 0;
}
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public void run() { // called by scheduler
System.out.println("Running watcher");
/* Set up to call the weather service. */
String weatheruri =
“http://mccarthy.heinz.cmu.edu:8001/servlet/GetWeather”+
“/weather.xml";
/* For simplicity we won’t take the appropriate approach. */
/* String weatheruri =
"http://mccarthy.heinz.cmu.edu:8001/servlet/GetWeather/?city="
+ URLEncoder.encode(this.city);
*/
/* Create an InputSource object for the parser to use. */
InputSource is = new InputSource(weatheruri);
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try {
/* Set up to handle incoming XML */
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(true);
SAXParser parser = factory.newSAXParser();
parser.parse(is, this); /* The parser makes the calls. */
}
catch(Exception e) {
e.printStackTrace();
return;
}
/* The parsing and callbacks are done by this time. */
int currentTempNumber;
try {
currentTempNumber = Integer.parseInt(this.currentTemp.trim());
}
catch( NumberFormatException e) {e.printStackTrace(); return; }
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/* See if the user wants to be alerted. */
if(currentTempNumber > this.temp) {
this.overTemp++;
if(this.overTemp >= this.duration) {
warning();
}
}
else {
this.overTemp = 0;
}
}
/* Send email via JavaMail. The Mailer class is based on the JavaMail API. */
public void warning() {
System.out.println("Sending email");
Mailer mailman = new Mailer(this.user,
"[email protected]", "It's hot");
mailman.send();
}
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/* Handle SAX events. */
StringBuffer buffer;
String currentTemp;
public void startDocument() throws SAXException {
this.currentTemp = null;
}
public void startElement(String name, AttributeList aMap) throws SAXException {
if(name.equals("CurrTemp")) { /* Prepare for next event. */
this.buffer = new StringBuffer();
}
}
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public void endElement(String name) throws SAXException {
if(name.equals("CurrTemp")) {
this.currentTemp = this.buffer.toString();
this.buffer = null;
}
}
public void characters(char[] ch, int start, int length) throws SAXException {
if(this.buffer != null) this.buffer.append(ch,start,length);
}
}
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WeatherReport
application
Mobile users
WML
HTML
XML
PC users
Http://www.xweather.com
PowerWarning
application
XML
Email notifications
XML
Application
programs
Registrations
Internet Technologies
30
