Week 5

1. 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. Internet Technologies

2. 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. Internet Technologies

3. Unrelated threads 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(); } } } Internet Technologies

4. 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(); } } } Internet Technologies

5. 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"); } } Internet Technologies

6. Output 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 Main finishes right away Threads are sharing time This program has three threads. Internet Technologies

7. Unrelated Threads Part II • 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. Internet Technologies

8. 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()); } } } Internet Technologies

9. 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()); } } } Internet Technologies

10. 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"); } } Internet Technologies

11. 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 After “I like coffee”, the coffee thread goes to sleep and the tea thread gets to finish and die. 1 second pausing after each “I like coffee” Internet Technologies

12. 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. Internet Technologies

13. 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. Internet Technologies

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

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

16. 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; } Internet Technologies

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

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

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

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

21. // 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; Internet Technologies

22. // 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(); Internet Technologies

23. // 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"); Internet Technologies

24. // 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) { } } Internet Technologies

25. // 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); Internet Technologies

26. // 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); } } Internet Technologies

27. 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 < 0 || thePort > 65535) thePort = 80; } catch(Exception e) { thePort = 80; } Internet Technologies

28. // 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 Internet Technologies

29. 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. Internet Technologies

30. Suppose that we know that the weather information is available from the web at http://www.xweather.com/White_Plains_NY_US.html. [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&#176;</td></tr> [10] <tr><td>Today’s High</td><td align=center>82&#176;</td></tr> [11] <tr><td>Today’s Low</td><td align=center>62&#176;</td><tr> [12] </table> [13] </body> [14] </html> Internet Technologies

31. 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… Internet Technologies

32. <?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 Internet Technologies

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

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

35. 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 behind Jigsaw in the file Www/weather/ weather.xml. Perhaps this is being served up by www.xweather.com for ½ cents per hit. Internet Technologies

36. 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. Internet Technologies

37. 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); Internet Technologies

38. 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(); } } Internet Technologies

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

40. 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> Internet Technologies

41. 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. Internet Technologies

42. 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 { Internet Technologies

43. 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. */ Internet Technologies

44. 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")); Internet Technologies

45. /* 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(); } } Internet Technologies

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

47. 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(); } Internet Technologies

48. 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. Internet Technologies

49. 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. Internet Technologies

50. 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; Internet Technologies