1. Internet Technologies Week 5 Preliminaries to XML Messaging Introductory Java Threads A multi-threaded server XML Messaging A PowerWarning application using SAX A DOM example Building a DOM Tree from Scratch Thread examples taken from “The Java Programming Language” By Arnold and Gosling and from Cay Horstmann’s “Core Java 2 Advanced”. The PowerWarning Application is from “XML and Java” by Maruyama, Tamura, and Uramoto, Addison-Wesley.

2. Internet Technologies Four kinds of thread programming 1) Unrelated threads 2) Related but unsynchronized threads 3) Mutually-exclusive threads 4) Communicating mutually-exclusive threads We will look at the first two (simple) kinds.

3. Internet Technologies class Coffee extends Thread { Coffee(String name) { super(name); } public void run() { for(int n = 1; n <= 3; n++) { System.out.println("I like coffee"); yield(); System.out.println(this.getName()); yield(); } Unrelated threads

4. Internet Technologies class Tea extends Thread { Tea(String name) { super(name); } public void run() { for(int n = 1; n <= 3; n++) { System.out.println("I like tea"); yield(); System.out.println(this.getName()); yield(); }

5. Internet Technologies public class Drinks { public static void main(String args[]) { System.out.println("I am main"); Coffee t1 = new Coffee("Wawa Coffee"); Tea t2 = new Tea(“Sleepy Time Tea"); t1.start(); t2.start(); System.out.println("Main is done"); }

6. Internet Technologies I am main Main is done I like coffee I like tea Wawa Coffee Sleepy Time Tea I like coffee I like tea Wawa Coffee Sleepy Time Tea I like coffee I like tea Wawa Coffee Sleepy Time Tea Output Main finishes right away Threads are sharing time This program has three threads.

7. Internet Technologies Using sleep() in unrelated threads The call sleep(millis) puts the currently executing thread to sleep for at least the specified number of milliseconds. "At least“ means there is no guarantee the thread will wake up in exactly the specified time. Other thread scheduling can interfere. Unrelated Threads Part II

8. Internet Technologies class Coffee extends Thread { Coffee(String name) { super(name); } public void run() { for(int n = 1; n <= 3; n++) { System.out.println("I like coffee"); try { sleep(1000); // 1 second } catch(InterruptedException e) {} System.out.println(this.getName()); }

9. Internet Technologies class Tea extends Thread { Tea(String name) { super(name); } public void run() { for(int n = 1; n <= 5; n++) { System.out.println("I like tea"); System.out.println(getName()); }

10. Internet Technologies public class Drinks2 { public static void main(String args[]) { System.out.println("I am main"); Coffee t1 = new Coffee("Wawa Coffee"); Tea t2 = new Tea(“Sleepy Time Tea"); t1.start(); t2.start(); System.out.println("Main is done"); }

11. Internet Technologies I am main Main is done I like coffee I like tea Sleepy Time Tea I like tea Sleepy Time Tea I like tea Sleepy Time Tea I like tea Sleepy Time Tea I like tea Sleepy Time Tea Wawa Coffee I like coffee Wawa Coffee I like coffee Wawa Coffee 1 second pausing after each “I like coffee” After “I like coffee”, the coffee thread goes to sleep and the tea thread gets to finish and die.

12. Internet Technologies Yield() and Sleep() Yield() may have no effect on some implementations. The thread scheduler might make no effort toward fairness. The yielding thread may be picked again even though other threads want a turn. It is a good idea to call sleep() instead.

13. Internet Technologies Ping Pong Adapted from "The Java Programming Language", Arnold and Gosling After a thread is created, you can configure it – set its name, its initial priority (system dependent), and so on. The start() method spawns a new thread of control based on the data in the thread object and then returns. Now, the Java virtual machine invokes the new thread's run method, making the thread active. When a thread's run method returns, the thread has exited. The thread may be manipulated with a number of methods, including the interrupt() method as shown in this example.

14. Internet Technologies public class PingPong extends Thread { private String word; private int delay; public PingPong(String whatToSay, int delayTime) { word = whatToSay; delay = delayTime; } Each PingPong object knows what to say and how long to sleep.

15. Internet Technologies public void run() { try { for(;;) { System.out.println(word+" "); sleep(delay); } catch (InterruptedException e) { System.out.println("Interrupted!!!!!"); return; }

16. Internet Technologies public static void main(String args[]) { PingPong t1 = new PingPong("\tping",33); t1.start(); PingPong t2 = new PingPong("Pong",100); t2.start(); try { Thread.sleep(5000); } catch(InterruptedException e) { // will not be printed System.out.println("Good morning"); return; }

17. Internet Technologies Thread myThread = Thread.currentThread(); for (int t = 1 ; t <= 10; t++) System.out.println("In Main..." + myThread.getName()); t1.interrupt(); }

18. Internet Technologies C:\McCarthy\threads\PingPong>java PingPong ping Pong ping Pong ping Pong ping : Main is asleep. For 5 seconds ping and pong take turns sleeping and running

19. Internet Technologies Pong ping Pong In Main...main Interrupted!!!!! Pong : “Pongs” forever or until until ctrl-c Main wakes up Main interrupts Ping and ping dies.

20. Internet Technologies A Thread Application --A Simple Web Server Responds by sending the same file on each hit Creates a new thread on each hit

21. Internet Technologies // A simple multi-threaded web server import java.net.*; import java.io.*; import java.util.*; public class OneFile extends Thread { static String theData = ""; static String contentType; static int contentLength; Socket theConnection;

22. Internet Technologies // construct each OneFile object with an existing socket public OneFile(Socket s) { theConnection = s; } // run the following code on each object public void run() { try { // get a PrintStream attached to this socket PrintStream os = new PrintStream( theConnection.getOutputStream()); // get a DataInputStream attached to this socket DataInputStream is = new DataInputStream( theConnection.getInputStream()); // read a line from the socket String request = is.readLine();

23. Internet Technologies // HTTP/1.0 and later send a MIME header if(request.indexOf("HTTP/") != -1) { // we need to read the rest of the MIME header while(true) { String thisLine = is.readLine(); if(thisLine.trim().equals("")) break; } // respond to the client os.print("HTTP/1.0 200 OK\r\n"); // send the date Date now = new Date(); os.print("Date: " + now + "\r\n"); // send our name os.print("Server: OneFile 1.0\r\n");

24. Internet Technologies // send the contentLength os.print("Content-length: " + contentLength + "\r\n"); // send the content type os.print("Content-type: " + contentType + "\r\n\r\n"); } // send the file in the string os.println(theData); theConnection.close(); } catch(IOException e) { }

25. Internet Technologies // main loads the file and creates the object on every hit public static void main(String args[] ) { int thePort; ServerSocket ss; Socket theConnection; FileInputStream theFile; // cache the file try { // open file and create a DataInputStream theFile = new FileInputStream(args[0]); DataInputStream dis = new DataInputStream(theFile);

26. Internet Technologies // determine the content type of this file if(args[0].endsWith(".html") || args[0].endsWith(".htm") ) { contentType = "text/html"; } else { contentType = "text/plain"; } // read the file into the string theData try { String thisLine; while((thisLine = dis.readLine()) != null) { theData += thisLine + "\n"; } catch(Exception e) { System.err.println("Error " + e); }

27. Internet Technologies catch(Exception e) { System.err.println(e); System.err.println("usage: java onefile filename port"); System.exit(1); } // set the port to listen on try { thePort = Integer.parseInt(args[1]); if(thePort 65535) thePort = 80; } catch(Exception e) { thePort = 80; }

28. Internet Technologies // create a server socket try { ss = new ServerSocket(thePort); System.out.println("Accepting connections on port " + ss.getLocalPort()); System.out.println("Data to be sent:"); System.out.println(theData); while(true) { // stop and wait for a connection Socket socketTemp = ss.accept(); // we have a socket so create a handler OneFile fs = new OneFile(socketTemp); // start the handler running fs.start(); } catch(IOException e) {System.out.println("Socket error"); } } Start thread

29. Internet Technologies Example: XML Messaging 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.

30. Internet Technologies [1] [2] [3] Weather Report [4] [5] [6] Weather Report -- White Plains, NY [7] [8] Date/Time 11 AM EDT Sat Jul 25 1998 [9] Current Tem. 70° [10] Today’s High 82° [11] Today’s Low 62° [12] [13] [14] Suppose that we know that the weather information is available from the web at http://www.xweather.com/White_Plains_NY_US.html.

31. Internet Technologies 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 tag, then go to the second tag within the table, and then go to the second tag within the row. Neither of these seems very appealing…

32. Internet Technologies <!DOCTYPE WeatherReport SYSTEM “http>//www.xweather.com/WeatherReport.dtd”> White Plains NY Sat Jul 25 1998 11 AM EDT 70 82 62 XML would help

33. Internet Technologies Strategy 3: For the current temperature of White Plains, N.Y., go to the tag.

34. Internet Technologies XML Mobile users PC users Http://www.xweather.com WeatherReport application WML HTML PowerWarning application Application programs XML Email notifications Registrations XML XSLT

35. Internet Technologies The XML Describing the Weather Pittsburgh PA Wed. April 11, 2001 3 70 82 62 This file is behind Jigsaw in the file Www/weather/ weather.xml. Perhaps this is being served up by www.xweather.com www.xweather.com for ½ cents per hit.

36. Internet Technologies 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 not normally be retrieved from a file. It costs ½ cent per hit.

37. Internet Technologies 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);

38. Internet Technologies 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(); }

39. Internet Technologies XML Mobile users PC users Http://www.xweather.com WeatherReport application WML HTML PowerWarning application Application programs XML Email notifications Registrations XML XSLT

40. Internet Technologies Registrations (HTML) PowerWarning E-Mail State City Temperature Duration

41. Internet Technologies Registrations (Servlet) 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. 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.

42. Internet Technologies 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 {

43. Internet Technologies 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. */

44. Internet Technologies 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"));

45. Internet Technologies /* 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(" ” + “You'll be notified by email "); writer.close(); }

46. Internet Technologies mm6@andrew.cmu.edu w@whitehouse.gov PowerWarn.userTable User data Watcher Scheduler Http Request Email Servlet

47. Internet Technologies 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(); }

48. Internet Technologies 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.

49. Internet Technologies 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?

50. Internet Technologies 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;

51. Internet Technologies 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; }

52. Internet Technologies 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”+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);

53. Internet Technologies 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; }

54. Internet Technologies /* 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(); }

55. Internet Technologies /* 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(); }

56. Internet Technologies 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); } }

57. Internet Technologies XML Mobile users PC users Http://www.xweather.com WeatherReport application WML HTML PowerWarning application Application programs XML Email notifications Registrations XML

58. Internet Technologies Building a DOM Tree From Scratch 100 Let’s create this file from within a java program. MyGradeBook.xml

59. Internet Technologies // DomExample.java // Building an xml document from scratch import java.io.*; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.ParserConfigurationException; import org.w3c.dom.*; import com.sun.xml.tree.XmlDocument; public class DomExample { private Document document;

60. Internet Technologies // Get an empty Document object public DomExample () { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); try { DocumentBuilder builder = factory.newDocumentBuilder(); document = builder.newDocument(); } catch (Throwable t) { t.printStackTrace (); }

61. Internet Technologies // Ask the Document object for various types of nodes and // add them to the tree. Element root = document.createElement("GradeBook"); document.appendChild(root); Element student = document.createElement("Student"); root.appendChild(student); Element score = document.createElement("Score"); student.appendChild(score); Text value = document.createTextNode("100"); score.appendChild(value);

62. Internet Technologies // Write the Document to disk. try { FileOutputStream fos = new FileOutputStream("MyGradeBook.xml"); ((XmlDocument)document).write(fos); } catch(IOException ioe) { ioe.printStackTrace(); } public static void main(String a[]) { DomExample tree = new DomExample(); }