初识网络爬虫

初识网络爬虫

http://blog.csdn.net/luojinping/article/details/6870898

 

package SearchCrawler;

import java.util.*;
import java.net.*;
import java.io.*;
import java.util.regex.*;

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 forreading.
			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) {

		System.out.println("searchString=" + searchString);
		HashSet<String> crawledList = new HashSet<String>();
		LinkedHashSet<String> toCrawlList = new LinkedHashSet<String>();

		if (maxUrls < 1) {
			errorList.add("InvalidMax URLs value.");
			System.out.println("Invalid Max URLs value.");
		}

		if (searchString.length() < 1) {
			errorList.add("Missing SearchString.");
			System.out.println("Missing searchString");
		}

		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 toaccess 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) {
 
		String[] strs = {"http://www.sina.com","9","java"};
		int max = Integer.parseInt(strs[1]);
		SearchCrawler crawler = new SearchCrawler(strs[0], max, strs[2]);
		Thread search = new Thread(crawler);
		System.out.println("Start searching...");
		System.out.println("result:");
		search.start();

	}
}