基于JAVA语言的网络爬虫

Introduction：

这个小demo用于爬取淘宝网的相关链接。

首先从“www.taobao.com"这个url开始，手机页面上的所有url，然后存入toCrawList 。当toCrawList不为空时，拿出一个url,把它存入数据集并且搜寻这个url上的所有链接充入toCrawList. 这是一个BFS过程。

Framework:

Code:

就网络爬虫来讲这个demo没有太多特别之处，只是根据项目需求，最大的爬取url数有个限制，因此效率上会相对的做出一些优化。另外为了防止URL.openStream()时失去响应，初次尝试使用了java中为方法设置超时时间的模块。

主函数：

public static void main(String[] args) {can_be_stopped = false;if (args.length != 3) {System.out.println("Usage:java SearchCrawler startUrl maxUrl searchString");}String[] paramers = new String[3];paramers[0] = "http://www.taobao.com";paramers[1] = "10000";paramers[2] = "java";int max = Integer.parseInt(paramers[1]);dapa crawler = new dapa(paramers[0], max, paramers[2]);Thread search = new Thread(crawler);System.out.println("Start searching...");System.out.println("result:");search.start();}

第一个参数是爬取得首地址，第二个参数是最大爬取得url数（为了优化，代码中对toCrawList的大小也进行了限制。例如我想爬取8000个URL，那么toCrawList如果大于8000，则停止对toCrawList的扩充）。第三个参数无意义。

 在下载页面时，为了防止openStream卡住，我通过java自带的方法来对openStream设置了超时时间，实现时使用代理模式：

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();//int count=1;while ((line = reader.readLine()) != null) {pageBuffer.append(line);}return pageBuffer.toString();} catch (Exception e) {}return null;}private String DownloadPage(URL pageUrl){//String page=null; final URL thePage=pageUrl; final ExecutorService exec = Executors.newFixedThreadPool(1);      Callable<String> call = new Callable<String>() {           public String call() throws Exception {                      return downloadPage(thePage);          }       };          try {           Future<String> future = exec.submit(call);           // set db connection timeout to 10 seconds           String obj = future.get(1000 * 30, TimeUnit.MILLISECONDS);            return obj;             } catch (TimeoutException ex) {           System.out.println("====================task time out===============");           ex.printStackTrace();                } catch (Exception e) {           System.out.println("failed to handle.");           e.printStackTrace();       }       // close thread pool       exec.shutdown();       return null;}

为了防止程序异常结束或超时，每获取一条url我都要把它添加至文件末尾。 当然大量的文件操作也影响了程序的效率。

File file = new File("D:/scope/url3.txt");BufferedWriter bw = null;try {bw = new BufferedWriter(new FileWriter(file, true));bw.write(url + "\r\n");bw.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}

完整程序：

package snippet;import java.sql.Connection;import java.util.*;import java.net.*;import java.beans.Statement;import java.io.*;import java.util.concurrent.Callable;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;import java.util.concurrent.TimeUnit;import java.util.concurrent.TimeoutException;import java.util.regex.*;import javax.sql.DataSource;// 搜索Web爬行者public class dapa 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ArrayList<String> checklist = new ArrayList<String>(); 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int totcount=0;private static boolean can_be_stopped = false;public dapa(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try {crawl(startUrl, maxUrl, searchString, limitHost, caseSensitive);} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println("over");}// 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;if (url.matches(".*//.*//.*"))return 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();//int count=1;while ((line = reader.readLine()) != null) {pageBuffer.append(line);}return pageBuffer.toString();} catch (Exception e) {}return null;}private String DownloadPage(URL pageUrl){//String page=null; final URL thePage=pageUrl; final ExecutorService exec = Executors.newFixedThreadPool(1);      Callable<String> call = new Callable<String>() {           public String call() throws Exception {                      return downloadPage(thePage);          }       };          try {           Future<String> future = exec.submit(call);           // set db connection timeout to 10 seconds           String obj = future.get(1000 * 30, TimeUnit.MILLISECONDS);            return obj;             } catch (TimeoutException ex) {           System.out.println("====================task time out===============");           ex.printStackTrace();                } catch (Exception e) {           System.out.println("failed to handle.");           e.printStackTrace();       }       // close thread pool       exec.shutdown();       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,HashSet toCrawlList) throws Exception {// 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) {continue;/* * 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; } } */// link=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;}//化简link = SimpleUrl(link);// 跳过那些已经处理的链接.if (crawledList.contains(link)) {continue;}if (toCrawlList.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) {return true;/* * 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)throws Exception {System.out.println("searchString=" + searchString);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wwwstartUrl = 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crawledListcrawledList.add(url);if (!can_be_stopped) {System.out.println("--downloadPage..");String pageContents = DownloadPage(verifiedUrl);if (pageContents != null && pageContents.length() > 0) {// 从页面中获取有效的链接System.out.println("--retrieveLinks..");ArrayList<String> links = retrieveLinks(verifiedUrl,pageContents, crawledList, limitHost,toCrawlList);// 控制toCrawlList最大容量// if(toCrawlList.size()<100000)if(!links.isEmpty())toCrawlList.addAll(links);// toCrawlList超过最大搜索数即可不再充入urlif (toCrawlList.size() > 10000)can_be_stopped = true;}}System.out.println("toCrawList:" + toCrawlList.size());//if (searchStringMatches(pageContents, searchString,//caseSensitive)) {result.add(url);System.out.println("crawledList:" +crawledList.size());System.out.println(url);File file = new File("D:/scope/url3.txt");BufferedWriter bw = null;try {bw = new BufferedWriter(new FileWriter(file, true));bw.write(url + "\r\n");bw.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}//}}return result;}String SimpleUrl(String url) throws Exception { URL uri =new URL(url); String result ="http://"+ uri.getHost()+uri.getPath(); return result; }// 主函数public static void main(String[] args) {can_be_stopped = false;if (args.length != 3) {System.out.println("Usage:java SearchCrawler startUrl maxUrl searchString");}String[] paramers = new String[3];paramers[0] = "http://www.taobao.com";paramers[1] = "10000";paramers[2] = "java";int max = Integer.parseInt(paramers[1]);dapa crawler = new dapa(paramers[0], max, paramers[2]);Thread search = new Thread(crawler);System.out.println("Start searching...");System.out.println("result:");search.start();}}

输出：

Usage:java SearchCrawler startUrl maxUrl searchStringStart searching...result:searchString=java--downloadPage..--retrieveLinks..toCrawList:53crawledList:1http://taobao.com--downloadPage..--retrieveLinks..toCrawList:84crawledList:2http://style.taobao.com--downloadPage..--retrieveLinks..toCrawList:92crawledList:3http://daogou.taobao.com/market/236/searchAuction.htm--downloadPage..--retrieveLinks..toCrawList:107crawledList:4http://miiee.taobao.com/themes/theme_333.htm--downloadPage..toCrawList:104crawledList:5http://reg.taobao.com/member/new_register.jhtml--downloadPage..toCrawList:103crawledList:6http://i.taobao.com/my_taobao.htm--downloadPage..toCrawList:102crawledList:7http://vip.taobao.com/growth_info.htm..