Internet Technologies Week 5 Preliminaries to XML Messaging Introductory Java Threads A...

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.


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.


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


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();

} }}


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");}

}


I am mainMain is doneI like coffeeI like teaWawa CoffeeSleepy Time TeaI like coffeeI like teaWawa CoffeeSleepy Time TeaI like coffeeI like teaWawa CoffeeSleepy Time Tea

Output

Main finishes right away

Threads are sharing time

This program has three threads.


• 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


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());

}}

}


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());

}}

}


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"); }}


I am mainMain is doneI like coffeeI like teaSleepy Time TeaI like teaSleepy Time TeaI like teaSleepy Time TeaI like teaSleepy Time TeaI like teaSleepy Time TeaWawa CoffeeI like coffeeWawa CoffeeI like coffeeWawa 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.


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.


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.


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.


public void run() { try {

for(;;) { System.out.println(word+" "); sleep(delay);

} } catch (InterruptedException e) { System.out.println("Interrupted!!!!!");

return; }}


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 printedSystem.out.println("Good morning");

return; }


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


C:\McCarthy\threads\PingPong>java PingPong pingPong ping ping pingPong ping ping pingPong ping ping ping : :

Main is asleep.

For 5 secondsping and pongtake turns sleepingand running


Pong ping ping pingPongIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainInterrupted!!!!!PongPongPongPongPong:

“Pongs” foreveror until until ctrl-c

Main wakes up

Main interruptsPing and ping dies.


A Thread Application --A Simple Web Server

• Responds by sending the same file on each hit

• Creates a new thread on each hit


// 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;


// 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();


// 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");


// 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) { } }


// 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);


// 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); } }


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; }


// 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


Example: XML Messaging

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.


[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.


•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…


<?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


•Strategy 3:

For the current temperature of White Plains, N.Y., go to the <CurrTemp> tag.


XML

Mobile users

PC usersHttp://www.xweather.com

WeatherReportapplication

WML

HTML

PowerWarningapplication

Applicationprograms

XML

Email notifications

RegistrationsXML

XSLT


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.

http://www.xweather.com/


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.

It costs ½ cent per hit.


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);


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(); }}


XML

Mobile users



WML

HTML


Applicationprograms

XML

Email notifications

RegistrationsXML

XSLT


Registrations (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>


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.


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 {


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. */


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"));


/* 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(); }

}


[email protected]

[email protected]

PowerWarn.userTable

User data

User data

User data

User data

Watcher

Watcher

Scheduler

Http Request

Http Request

Email

Email

Servlet


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(); }


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.


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?


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;


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; }


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);

http://mccarthy.heinz.cmu.edu:8001/servlet/GetWeather

http://mccarthy.heinz.cmu.edu:8001/servlet/GetWeather


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; }


/* 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();}


/* 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();

} }


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);

} }


XML

Mobile users



WML

HTML


Applicationprograms

XML

Email notifications

RegistrationsXML


Building a DOM Tree From Scratch

<?xml version="1.0" encoding="UTF-8"?>

<GradeBook> <Student> <Score>100</Score> </Student></GradeBook>

Let’s create this filefrom within a javaprogram.

MyGradeBook.xml


// 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;


// Get an empty Document object public DomExample () {

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); try {

DocumentBuilder builder = factory.newDocumentBuilder(); document = builder.newDocument();

} catch (Throwable t) {

t.printStackTrace (); }


// 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);


// 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(); }}

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Internet Technologies Week 5 Preliminaries to XML Messaging Introductory Java Threads A...

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