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Learn how to process form data and create dynamic web elements using servlets in Java. Explore form evaluation techniques, request methods, and response handling for user interaction on web servers.
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Servlet II • Anwendungen • Formular Auswertung • Zähler • Zähler mit Zwischenspeicherung • Hintergrund Berechnung • Passwort Abfrage
Get Request Response Post Request Response Auswertung eines Formulars http://www.sdf.... Webserver index.html Servlet Container processformular
<FORM> • <form method="POST" action="processformular"> • <input type="text" name=name size=50 > • <input type="submit" > • </form> HTML
Auswertung • package counter; • import javax.servlet.*; • import javax.servlet.http.*; • import java.io.*; • import java.util.*; • public class formular extends HttpServlet { • private static final String CONTENT_TYPE = "text/html"; • public void init() throws ServletException { } • public void doPost(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException { • response.setContentType(CONTENT_TYPE); • PrintWriter out = response.getWriter(); • String name = req.getParameter("name"); • String s1 = req.getParameter("is-gift"); • String s2 = req.getParameter("address-line-1"); • String s3 = req.getParameter("address-line-2"); • String s4 = req.getParameter("city");
Auswertung • String s5 = req.getParameter("state"); • String s6 = req.getParameter("country"); • String s7 = req.getParameter("phone-number"); • String s8 = req.getParameter("shipping-billing"); • out.println("<HTML>"); • out.println("<HEAD><TITLE>Formular</TITLE></HEAD>"); • out.println("<BODY>"); • out.println("Name: " + name +"<BR>"); • out.println("Geschenk: " + s1 +"<BR>"); • out.println("Adr: " + s2 +"<BR>"); • out.println("Adr2: " + s3 +"<BR>"); • out.println("Stadt: " + s4 +"<BR>"); • out.println("Land: " + s6 +"<BR>"); • out.println("Tel: " + s7 +"<BR>"); • out.println("Rechnung: " + s8 +"<BR>"); • out.println("</BODY></HTML>"); • } • public void destroy() {} • }
Simple Counter • package counter; • import java.io.*; • import javax.servlet.*; • import javax.servlet.http.*; • public class SimpleCounter extends HttpServlet { • int count = 0; • public void doGet(HttpServletRequest req, HttpServletResponse res) • throws ServletException, IOException { • res.setContentType("text/plain"); • PrintWriter out = res.getWriter(); • count++; • out.println("Since loading, this servlet has been accessed " + count + " times."); • } • }
Daten Inkonsistenz • Kein Problem bei lokalen Variablen • Vorsicht bei Instanz Variablen • Bsp: Simple Counter • count++; // Thread 1 • count++; // Thread 2 • out.println("Since loading, ….. // Thread 1 • out.println("Since loading, ….. // Thread 2 • Hilfe: synchronized Blocks: • Nur ein einzelner Thread darf einen synchronized Block ausführen
Simple Counter synchronized • package counter; • import java.io.*; • import javax.servlet.*; • import javax.servlet.http.*; • public class SimpleCounter extends HttpServlet { • int count = 0; • public void doGet(HttpServletRequest req, HttpServletResponse res) • throws ServletException, IOException { • res.setContentType("text/plain"); • PrintWriter out = res.getWriter(); • synchronized(this) { count++; • out.println("Since loading, this servlet has been accessed "+count +" times."); • } • } • }
Counter II • package counter; • import java.io.*; • import java.util.*; • import javax.servlet.*; • import javax.servlet.http.*; • public class HolisticCounter extends HttpServlet { • static int classCount = 0; // verteilt auf alle Instanzen • int count = 0; // Nur für dieses Servlet • static Hashtable instances = new Hashtable(); // verteilt auf alle Instanzen • public void doGet(HttpServletRequest req, HttpServletResponse res) • throws ServletException, IOException { • res.setContentType("text/plain"); • PrintWriter out = res.getWriter(); • count++; • out.println("Since loading, this servlet instance has been accessed " + • count + " times.");
Counter II • // Trick: Die Instanzen werden gezählt, indem sie in eine • // Hashtable eingetragen werden. Gleiche Einträge werden ignoriert. • // Die size() Methode liefert die Zahl der einzelnen Instanzen. • instances.put(this, this); • out.println("There are currently " + • instances.size() + " instances."); • classCount++; • out.println("Across all instances, this servlet class has been " + • "accessed " + classCount + " times."); • } • }
Lebenszyklus • Initialisierung • Antworten auf Anfragen • Zerstörung • Persistenz • DB Verbindung • Information von früheren Transaktionen
Counter III • package counter; • import java.io.*; • import javax.servlet.*; • import javax.servlet.http.*; • public class InitDestroyCounter extends HttpServlet { • int count; • public void init() throws ServletException { • // Versuch den gespeicherten Zustand des Zählers zu laden • FileReader fileReader = null; • BufferedReader bufferedReader = null; • try { • fileReader = new FileReader("InitDestroyCounter.initial"); • bufferedReader = new BufferedReader(fileReader); • String initial = bufferedReader.readLine(); • count = Integer.parseInt(initial); • return; • }
InitDestroyCounter • catch (FileNotFoundException ignored) { } // kein gespeicherter Zähler • catch (IOException ignored) { } // Problem beim lesen • catch (NumberFormatException ignored) { } // Korruptes File • finally { • // Schliessen des Files • try { • if (bufferedReader != null) {bufferedReader.close(); • } • } • catch (IOException ignored) { } • } • // Überprüfe ob ein Initialisierungsparameter vorhanden ist. • String initial = getInitParameter("initial"); • try { • count = Integer.parseInt(initial); • return; • } • catch (NumberFormatException ignored) { } // null or non-integer value • // Default 0 • count = 0; • }
InitDestroyCounter • public void doGet(HttpServletRequest req, HttpServletResponse res) • throws ServletException, IOException { • res.setContentType("text/plain"); • PrintWriter out = res.getWriter(); • count++; • out.println("Since the beginning, this servlet has been accessed " + • count + " times."); • } • public void destroy() { • super.destroy(); • saveState(); • }
InitDestroyCounter • public void saveState() { • // Versuch den Counter zu speichern • FileWriter fileWriter = null; • PrintWriter printWriter = null; • try { • fileWriter = new FileWriter("InitDestroyCounter.initial"); • printWriter = new PrintWriter(fileWriter); • printWriter.println(count); • return; • } • catch (IOException e) { // Problem beim Schreiben • } • finally { • // Zur Sicherheit das File schliessen • if (printWriter != null) { • printWriter.close(); • } • } • } • }
PrimSearcher • package counter; • import java.io.*; • import java.util.*; • import javax.servlet.*; • import javax.servlet.http.*; • public class PrimeSearcher extends HttpServlet implements Runnable { • long lastprime = 0; // letzte gefundene Primzahl • Date lastprimeModified = new Date(); // Zeit • Thread searcher; // Hintergrund Thread • public void init() throws ServletException { • searcher = new Thread(this); • searcher.setPriority(Thread.MIN_PRIORITY); • searcher.start(); • } http://www.mindview.net/Books/DownloadSites/
PrimSearcher • public void run() { • long candidate = 1000000000000001L; • while (true) { • if (isPrime(candidate)) { • lastprime = candidate; // aktuelle Primzahl • lastprimeModified = new Date(); // Zeit der letzten gefunden Primzahl • } • candidate += 2; // keine geraden Primzahlen • try { • searcher.sleep(200); // an andere Prozesse denken • } • catch (InterruptedException ignored) { } • }
PrimSearcher • private static boolean isPrime(long candidate) { • // Dividiere die Zahl durch alle ungeraden Zahlen zwischen 3 und sqrt(z) • long sqrt = (long) Math.sqrt(candidate); • for (long i = 3; i <= sqrt; i += 2) { • if (candidate % i == 0) return false; // Ein Faktor gefunden • } • return true; //kein Faktor • } • public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { • res.setContentType("text/plain"); • PrintWriter out = res.getWriter(); • if (lastprime == 0) { • out.println("Still searching for first prime..."); • } • else { • out.println("The last prime discovered was " + lastprime); • out.println(" at " + lastprimeModified); • } • } • public void destroy() { searcher.stop();} • } http://archive.coreservlets.com/
Protected Page • package protectedpage; • import java.io.*; • import javax.servlet.*; • import javax.servlet.http.*; • import java.util.Properties; • import sun.misc.BASE64Decoder; • public class ProtectedPage extends HttpServlet { • private Properties passwords; • private String passwordFile; • public void init(ServletConfig config) • throws ServletException { • super.init(config); • try { • passwordFile = config.getInitParameter("passwordFile"); • passwords = new Properties(); • passwords.load(new FileInputStream(passwordFile)); • } catch(IOException ioe) {} • }
Protected Page • public void doGet(HttpServletRequest request, • HttpServletResponse response) • throws ServletException, IOException { • response.setContentType("text/html"); • PrintWriter out = response.getWriter(); • String authorization = request.getHeader("Authorization"); • if (authorization == null) { • askForPassword(response); • } else {
Protected Page • String userInfo = authorization.substring(6).trim(); • BASE64Decoder decoder = new BASE64Decoder(); • String nameAndPassword = new String(decoder.decodeBuffer(userInfo)); • int index = nameAndPassword.indexOf(":"); • String user = nameAndPassword.substring(0, index); • String password = nameAndPassword.substring(index+1); • String realPassword = passwords.getProperty(user); • if ((realPassword != null) && • (realPassword.equals(password))) { • String title = "Welcome to the Protected Page"; • out.println(ServletUtilities.headWithTitle(title) +
Protected Page • "<BODY BGCOLOR=\"#FDF5E6\">\n" + • "<H1 ALIGN=CENTER>" + title + "</H1>\n" + • "Congratulations. You have accessed a\n" + • "highly proprietary company document.\n" + • "Shred or eat all hardcopies before\n" + • "going to bed tonight.\n" + • "</BODY></HTML>"); • } else { • askForPassword(response); • } • } • }
Protected Page • private void askForPassword(HttpServletResponse response) { • response.setStatus(response.SC_UNAUTHORIZED); // Ie 401 • response.setHeader("WWW-Authenticate", • "BASIC realm=\"privileged-few\""); • } • /** Handle GET and POST identically. */ • public void doPost(HttpServletRequest request, • HttpServletResponse response) • throws ServletException, IOException { • doGet(request, response); • } • }
Praktikum • Kundenangaben mit PW Abfrage: • http Passwortabfrage • Formular mit Passwortabfrage • Alle Adressen im Container werden angezeigt. • Formular zur Eingabe von weiteren Adressen • (5.) Save & Edit & Delete
Ihr Job • 1.) • 3.) alle Daten anzeigen • 4.) Eingabe • 2.)