Java tutorial
/* Copyright 2004 Sun Microsystems, Inc. All rights reserved. You may not modify, use, reproduce, or distribute this software except in compliance with the terms of the License at:*/ //import java.applet.Applet; import java.awt.BorderLayout; import java.awt.Button; import java.awt.Choice; import java.awt.FlowLayout; import java.awt.Frame; import java.awt.Graphics; import java.awt.Label; import java.awt.List; import java.awt.Panel; import java.awt.TextField; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.io.IOException; import java.io.InputStream; import java.net.MalformedURLException; import java.net.URL; import java.net.URLConnection; import java.util.Properties; import java.util.StringTokenizer; import java.util.Vector; public class WebCrawler extends Applet implements ActionListener, Runnable { public static final String SEARCH = "Search"; public static final String STOP = "Stop"; public static final String DISALLOW = "Disallow:"; public static final int SEARCH_LIMIT = 50; Panel panelMain; List listMatches; Label labelStatus; // URLs to be searched Vector vectorToSearch; // URLs already searched Vector vectorSearched; // URLs which match Vector vectorMatches; Thread searchThread; TextField textURL; Choice choiceType; public void init() { // set up the main UI panel panelMain = new Panel(); panelMain.setLayout(new BorderLayout(5, 5)); // text entry components Panel panelEntry = new Panel(); panelEntry.setLayout(new BorderLayout(5, 5)); Panel panelURL = new Panel(); panelURL.setLayout(new FlowLayout(FlowLayout.LEFT, 5, 5)); Label labelURL = new Label("Starting URL: ", Label.RIGHT); panelURL.add(labelURL); textURL = new TextField("", 40); panelURL.add(textURL); panelEntry.add("North", panelURL); Panel panelType = new Panel(); panelType.setLayout(new FlowLayout(FlowLayout.LEFT, 5, 5)); Label labelType = new Label("Content type: ", Label.RIGHT); panelType.add(labelType); choiceType = new Choice(); choiceType.addItem("text/html"); choiceType.addItem("audio/basic"); choiceType.addItem("audio/au"); choiceType.addItem("audio/aiff"); choiceType.addItem("audio/wav"); choiceType.addItem("video/mpeg"); choiceType.addItem("video/x-avi"); panelType.add(choiceType); panelEntry.add("South", panelType); panelMain.add("North", panelEntry); // list of result URLs Panel panelListButtons = new Panel(); panelListButtons.setLayout(new BorderLayout(5, 5)); Panel panelList = new Panel(); panelList.setLayout(new BorderLayout(5, 5)); Label labelResults = new Label("Search results"); panelList.add("North", labelResults); Panel panelListCurrent = new Panel(); panelListCurrent.setLayout(new BorderLayout(5, 5)); listMatches = new List(10); panelListCurrent.add("North", listMatches); labelStatus = new Label(""); panelListCurrent.add("South", labelStatus); panelList.add("South", panelListCurrent); panelListButtons.add("North", panelList); // control buttons Panel panelButtons = new Panel(); Button buttonSearch = new Button(SEARCH); buttonSearch.addActionListener(this); panelButtons.add(buttonSearch); Button buttonStop = new Button(STOP); buttonStop.addActionListener(this); panelButtons.add(buttonStop); panelListButtons.add("South", panelButtons); panelMain.add("South", panelListButtons); add(panelMain); setVisible(true); repaint(); // initialize search data structures vectorToSearch = new Vector(); vectorSearched = new Vector(); vectorMatches = new Vector(); // set default for URL access URLConnection.setDefaultAllowUserInteraction(false); } public void start() { } public void stop() { if (searchThread != null) { setStatus("stopping..."); searchThread = null; } } public void destroy() { } boolean robotSafe(URL url) { String strHost = url.getHost(); // form URL of the robots.txt file String strRobot = "http://" + strHost + "/robots.txt"; URL urlRobot; try { urlRobot = new URL(strRobot); } catch (MalformedURLException e) { // something weird is happening, so don't trust it return false; } String strCommands; try { InputStream urlRobotStream = urlRobot.openStream(); // read in entire file byte b[] = new byte[1000]; int numRead = urlRobotStream.read(b); strCommands = new String(b, 0, numRead); while (numRead != -1) { if (Thread.currentThread() != searchThread) break; numRead = urlRobotStream.read(b); if (numRead != -1) { String newCommands = new String(b, 0, numRead); strCommands += newCommands; } } urlRobotStream.close(); } catch (IOException e) { // if there is no robots.txt file, it is OK to search return true; } // assume that this robots.txt refers to us and // search for "Disallow:" commands. String strURL = url.getFile(); int index = 0; while ((index = strCommands.indexOf(DISALLOW, index)) != -1) { index += DISALLOW.length(); String strPath = strCommands.substring(index); StringTokenizer st = new StringTokenizer(strPath); if (!st.hasMoreTokens()) break; String strBadPath = st.nextToken(); // if the URL starts with a disallowed path, it is not safe if (strURL.indexOf(strBadPath) == 0) return false; } return true; } public void paint(Graphics g) { //Draw a Rectangle around the applet's display area. g.drawRect(0, 0, getSize().width - 1, getSize().height - 1); panelMain.paint(g); panelMain.paintComponents(g); // update(g); // panelMain.update(g); } public void run() { String strURL = textURL.getText(); String strTargetType = choiceType.getSelectedItem(); int numberSearched = 0; int numberFound = 0; if (strURL.length() == 0) { setStatus("ERROR: must enter a starting URL"); return; } // initialize search data structures vectorToSearch.removeAllElements(); vectorSearched.removeAllElements(); vectorMatches.removeAllElements(); listMatches.removeAll(); vectorToSearch.addElement(strURL); while ((vectorToSearch.size() > 0) && (Thread.currentThread() == searchThread)) { // get the first element from the to be searched list strURL = (String) vectorToSearch.elementAt(0); setStatus("searching " + strURL); URL url; try { url = new URL(strURL); } catch (MalformedURLException e) { setStatus("ERROR: invalid URL " + strURL); break; } // mark the URL as searched (we want this one way or the other) vectorToSearch.removeElementAt(0); vectorSearched.addElement(strURL); // can only search http: protocol URLs if (url.getProtocol().compareTo("http") != 0) break; // test to make sure it is before searching if (!robotSafe(url)) break; try { // try opening the URL URLConnection urlConnection = url.openConnection(); urlConnection.setAllowUserInteraction(false); InputStream urlStream = url.openStream(); String type = urlConnection.guessContentTypeFromStream(urlStream); if (type == null) break; if (type.compareTo("text/html") != 0) break; // search the input stream for links // first, read in the entire URL byte b[] = new byte[1000]; int numRead = urlStream.read(b); String content = new String(b, 0, numRead); while (numRead != -1) { if (Thread.currentThread() != searchThread) break; numRead = urlStream.read(b); if (numRead != -1) { String newContent = new String(b, 0, numRead); content += newContent; } } urlStream.close(); if (Thread.currentThread() != searchThread) break; String lowerCaseContent = content.toLowerCase(); int index = 0; while ((index = lowerCaseContent.indexOf("<a", index)) != -1) { if ((index = lowerCaseContent.indexOf("href", index)) == -1) break; if ((index = lowerCaseContent.indexOf("=", index)) == -1) break; if (Thread.currentThread() != searchThread) break; index++; String remaining = content.substring(index); StringTokenizer st = new StringTokenizer(remaining, "\t\n\r\">#"); String strLink = st.nextToken(); URL urlLink; try { urlLink = new URL(url, strLink); strLink = urlLink.toString(); } catch (MalformedURLException e) { setStatus("ERROR: bad URL " + strLink); continue; } // only look at http links if (urlLink.getProtocol().compareTo("http") != 0) break; if (Thread.currentThread() != searchThread) break; try { // try opening the URL URLConnection urlLinkConnection = urlLink.openConnection(); urlLinkConnection.setAllowUserInteraction(false); InputStream linkStream = urlLink.openStream(); String strType = urlLinkConnection.guessContentTypeFromStream(linkStream); linkStream.close(); // if another page, add to the end of search list if (strType == null) break; if (strType.compareTo("text/html") == 0) { // check to see if this URL has already been // searched or is going to be searched if ((!vectorSearched.contains(strLink)) && (!vectorToSearch.contains(strLink))) { // test to make sure it is robot-safe! if (robotSafe(urlLink)) vectorToSearch.addElement(strLink); } } // if the proper type, add it to the results list // unless we have already seen it if (strType.compareTo(strTargetType) == 0) { if (vectorMatches.contains(strLink) == false) { listMatches.add(strLink); vectorMatches.addElement(strLink); numberFound++; if (numberFound >= SEARCH_LIMIT) break; } } } catch (IOException e) { setStatus("ERROR: couldn't open URL " + strLink); continue; } } } catch (IOException e) { setStatus("ERROR: couldn't open URL " + strURL); break; } numberSearched++; if (numberSearched >= SEARCH_LIMIT) break; } if (numberSearched >= SEARCH_LIMIT || numberFound >= SEARCH_LIMIT) setStatus("reached search limit of " + SEARCH_LIMIT); else setStatus("done"); searchThread = null; // searchThread.stop(); } void setStatus(String status) { labelStatus.setText(status); } public void actionPerformed(ActionEvent event) { String command = event.getActionCommand(); if (command.compareTo(SEARCH) == 0) { setStatus("searching..."); // launch a thread to do the search if (searchThread == null) { searchThread = new Thread(this); } searchThread.start(); } else if (command.compareTo(STOP) == 0) { stop(); } } public static void main(String argv[]) { Frame f = new Frame("WebFrame"); WebCrawler applet = new WebCrawler(); f.add("Center", applet); /* Behind a firewall set your proxy and port here! */ Properties props = new Properties(System.getProperties()); props.put("http.proxySet", "true"); props.put("http.proxyHost", "webcache-cup"); props.put("http.proxyPort", "8080"); Properties newprops = new Properties(props); System.setProperties(newprops); /**/ applet.init(); applet.start(); f.pack(); f.show(); } }