超简单的 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();  } }}

   超简单的 Web 爬虫程序，不过可以在他基础之上改造一下，写出强大点的爬虫！谢谢提供程序的 blog 友！