internet technologies1 xml messaging a powerwarning application using servlets and sax the...
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Internet Technologies 1
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 registertheir geographical position and their temperature concerns.
Users will receive e-mail when the temperature exceeds the userspecified 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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[1] <html>[2] <head>[3] <title>Weather Report</title>[4] </head>[5] <body>[6] <h2>Weather Report -- White Plains, NY </h2>[7] <table border=1>[8] <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>
Suppose that we know that the weather information is availablefrom the web at http://www.xweather.com/White_Plains_NY_US.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 nextampersand.
•Strategy 2:
For the current temperature of the White Plains, go to thefirst <table> tag, then go to the second <tr> tag within thetable, 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>
<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>
</Weather Report>
XML would help
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•Strategy 3:
For the current temperature of White Plains, N.Y., go to the <CurrTemp> tag.
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XML
Mobile users
PC usersHttp://www.xweather.com
WeatherReportapplication
WML
HTML
PowerWarningapplication
Applicationprograms
XML
Email notifications
RegistrationsXML
XSLT
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The XML Describing the Weather
<?xml version="1.0" encoding="UTF-8"?><WeatherReport> <City>Pittsburgh</City> <State>PA</State> <Date>Wed. April 11, 2001</Date> <Time>3</Time> <CurrTemp Unit = "Farenheit">70</CurrTemp> <High Unit = "Farenheit">82</High> <Low Unit = "Farenheit">62</Low> </WeatherReport>
This file is behindJigsaw in the fileWww/weather/weather.xml.
Perhaps this is being served upby 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.*;
public class GetWeather extends HttpServlet {
This data would notnormally be retrievedfrom a file.
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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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XML
Mobile users
PC usersHttp://www.xweather.com
WeatherReportapplication
WML
HTML
PowerWarningapplication
Applicationprograms
XML
Email notifications
RegistrationsXML
XSLT
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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)
On servlet initialization, we will start up an object whose responsibility it is to periodically wake up and tell the watcherobjects to check the weather.
The servlet will create a watcher object for each registered user. The watcher object will be told of each user’s locationand temperature requirements. Each watcher object will runin its own thread and may or may not notify its assigneduser by email.
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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 = req.getParameter("User"); String par_state = req.getParameter("State"); String par_city = req.getParameter("City"); int par_temp = 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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mm6@andrew.cmu.edu
w@whitehouse.gov
PowerWarn.userTable
User data
User data
User data
User data
Watcher
Watcher
Scheduler
Http Request
Http Request
Servlet
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The Schedulerimport 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 */ }
public Scheduler() { super(); }}
Fifteen seconds for testing.
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The Watcher Class
The Watcher objects make HTTP requests to get XML.
SAX.
JavaMail.
How should we handle the XML? SAX or DOM?
How do we send email?
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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, "mm6@andrew.cmu.edu", "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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XML
Mobile users
PC usersHttp://www.xweather.com
WeatherReportapplication
WML
HTML
PowerWarningapplication
Applicationprograms
XML
Email notifications
RegistrationsXML
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