一个简单的Web爬虫程序

/** * @author Jack.Wang * */ import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URL; import java.util.ArrayList; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedHashSet; import java.util.regex.Matcher; import java.util.regex.Pattern; // 搜索Web爬行者 public class SearchCrawler implements Runnable { /* * disallowListCache缓存robot不允许搜索的URL。 Robot协议在Web站点的根目录下设置一个robots.txt文件, * 规定站点上的哪些页面是限制搜索的。 * 搜索程序应该在搜索过程中跳过这些区域,下面是robots.txt的一个例子: * # robots.txt for http://somehost.com/ User-agent: * Disallow: /cgi-bin/ * Disallow: /registration # Disallow robots on registration page * Disallow: /login */ private HashMap<String, ArrayList<String>> disallowListCache = new HashMap<String, ArrayList<String>>(); ArrayList<String> errorList = new ArrayList<String>();// 错误信息 ArrayList<String> result = new ArrayList<String>(); // 搜索到的结果 String startUrl;// 开始搜索的起点 int maxUrl;// 最大处理的url数 String searchString;// 要搜索的字符串(英文) boolean caseSensitive = false;// 是否区分大小写 boolean limitHost = false;// 是否在限制的主机内搜索 public SearchCrawler(String startUrl, int maxUrl, String searchString) { this.startUrl = startUrl; this.maxUrl = maxUrl; this.searchString = searchString; } public ArrayList<String> getResult() { return result; } public void run() {// 启动搜索线程 crawl(startUrl, maxUrl, searchString, limitHost, caseSensitive); } // 检测URL格式 private URL verifyUrl(String url) { // 只处理HTTP URLs. if (!url.toLowerCase().startsWith("http://")) return null; URL verifiedUrl = null; try { verifiedUrl = new URL(url); } catch (Exception e) { return null; } return verifiedUrl; } // 检测robot是否允许访问给出的URL. private boolean isRobotAllowed(URL urlToCheck) { String host = urlToCheck.getHost().toLowerCase();// 获取给出RUL的主机 // System.out.println("主机="+host); // 获取主机不允许搜索的URL缓存 ArrayList<String> disallowList = disallowListCache.get(host); // 如果还没有缓存,下载并缓存。 if (disallowList == null) { disallowList = new ArrayList<String>(); try { URL robotsFileUrl = new URL("http://" + host + "/robots.txt"); BufferedReader reader = new BufferedReader( new InputStreamReader(robotsFileUrl.openStream())); // 读robot文件，创建不允许访问的路径列表。 String line; while ((line = reader.readLine()) != null) { if (line.indexOf("Disallow:") == 0) {// 是否包含"Disallow:" String disallowPath = line.substring("Disallow:" .length());// 获取不允许访问路径 // 检查是否有注释。 int commentIndex = disallowPath.indexOf("#"); if (commentIndex != -1) { disallowPath = disallowPath.substring(0, commentIndex);// 去掉注释 } disallowPath = disallowPath.trim(); disallowList.add(disallowPath); } } // 缓存此主机不允许访问的路径。 disallowListCache.put(host, disallowList); } catch (Exception e) { return true; // web站点根目录下没有robots.txt文件,返回真 } } String file = urlToCheck.getFile(); // System.out.println("文件getFile()="+file); for (int i = 0; i < disallowList.size(); i++) { String disallow = disallowList.get(i); if (file.startsWith(disallow)) { return false; } } return true; } private String downloadPage(URL pageUrl) { try { // Open connection to URL for reading. BufferedReader reader = new BufferedReader(new InputStreamReader( pageUrl.openStream())); // Read page into buffer. String line; StringBuffer pageBuffer = new StringBuffer(); while ((line = reader.readLine()) != null) { pageBuffer.append(line); } return pageBuffer.toString(); } catch (Exception e) { } return null; } // 从URL中去掉"www" private String removeWwwFromUrl(String url) { int index = url.indexOf("://www."); if (index != -1) { return url.substring(0, index + 3) + url.substring(index + 7); } return (url); } // 解析页面并找出链接 private ArrayList<String> retrieveLinks(URL pageUrl, String pageContents, HashSet crawledList, boolean limitHost) { // 用正则表达式编译链接的匹配模式。 Pattern p = Pattern.compile("<a//s+href//s*=//s*/"?(.*?)[/"|>]", Pattern.CASE_INSENSITIVE); Matcher m = p.matcher(pageContents); ArrayList<String> linkList = new ArrayList<String>(); while (m.find()) { String link = m.group(1).trim(); if (link.length() < 1) { continue; } // 跳过链到本页面内链接。 if (link.charAt(0) == '#') { continue; } if (link.indexOf("mailto:") != -1) { continue; } if (link.toLowerCase().indexOf("javascript") != -1) { continue; } if (link.indexOf("://") == -1) { if (link.charAt(0) == '/') {// 处理绝对地 link = "http://" + pageUrl.getHost() + ":" + pageUrl.getPort() + link; } else { String file = pageUrl.getFile(); if (file.indexOf('/') == -1) {// 处理相对地址 link = "http://" + pageUrl.getHost() + ":" + pageUrl.getPort() + "/" + link; } else { String path = file.substring(0, file.lastIndexOf('/') + 1); link = "http://" + pageUrl.getHost() + ":" + pageUrl.getPort() + path + link; } } } int index = link.indexOf('#'); if (index != -1) { link = link.substring(0, index); } link = removeWwwFromUrl(link); URL verifiedLink = verifyUrl(link); if (verifiedLink == null) { continue; } /* 如果限定主机，排除那些不合条件的URL */ if (limitHost && !pageUrl.getHost().toLowerCase().equals( verifiedLink.getHost().toLowerCase())) { continue; } // 跳过那些已经处理的链接. if (crawledList.contains(link)) { continue; } linkList.add(link); } return (linkList); } // 搜索下载Web页面的内容，判断在该页面内有没有指定的搜索字符串 private boolean searchStringMatches(String pageContents, String searchString, boolean caseSensitive) { String searchContents = pageContents; if (!caseSensitive) {// 如果不区分大小写 searchContents = pageContents.toLowerCase(); } Pattern p = Pattern.compile("[//s]+"); String[] terms = p.split(searchString); for (int i = 0; i < terms.length; i++) { if (caseSensitive) { if (searchContents.indexOf(terms[i]) == -1) { return false; } } else { if (searchContents.indexOf(terms[i].toLowerCase()) == -1) { return false; } } } return true; } // 执行实际的搜索操作 public ArrayList<String> crawl(String startUrl, int maxUrls, String searchString, boolean limithost, boolean caseSensitive) { HashSet<String> crawledList = new HashSet<String>(); LinkedHashSet<String> toCrawlList = new LinkedHashSet<String>(); if (maxUrls < 1) { errorList.add("Invalid Max URLs value."); System.out.println("Invalid Max URLs value."); } if (searchString.length() < 1) { errorList.add("Missing Search String."); System.out.println("Missing search String"); } if (errorList.size() > 0) { System.out.println("err!!!"); return errorList; } // 从开始URL中移出www startUrl = removeWwwFromUrl(startUrl); toCrawlList.add(startUrl); while (toCrawlList.size() > 0) { if (maxUrls != -1) { if (crawledList.size() == maxUrls) { break; } } // Get URL at bottom of the list. String url = toCrawlList.iterator().next(); // Remove URL from the to crawl list. toCrawlList.remove(url); // Convert string url to URL object. URL verifiedUrl = verifyUrl(url); // Skip URL if robots are not allowed to access it. if (!isRobotAllowed(verifiedUrl)) { continue; } // 增加已处理的URL到crawledList crawledList.add(url); String pageContents = downloadPage(verifiedUrl); if (pageContents != null && pageContents.length() > 0) { // 从页面中获取有效的链接 ArrayList<String> links = retrieveLinks(verifiedUrl, pageContents, crawledList, limitHost); toCrawlList.addAll(links); if (searchStringMatches(pageContents, searchString, caseSensitive)) { result.add(url); System.out.println(url); } } } return result; } // 主函数 public static void main(String[] args) { SearchCrawler crawler = new SearchCrawler("http://www.blogjava.net/Jack2007/", 20,"jack"); Thread search = new Thread(crawler); System.out.println("Start searching..."); System.out.println("result:"); search.start(); try { search.join(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }