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();

}

}

}