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标题: 搜索引擎----Java实现一个简单的网络爬虫最近正在研究 [打印本页]

作者: pi408637535 时间: 2015-7-16 16:30
标题: 搜索引擎----Java实现一个简单的网络爬虫最近正在研究
Java实现一个简单的爬虫程序。

package SearchCrawler;

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

/*
*搜索Web爬行者（起始的URL、处理url的最大数、要搜索的字符串)
*/
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)
{

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)
{
if (args.length != 3)
{
System.out
.println("Usage:java SearchCrawler startUrl maxUrl searchString");
return;
}
int max = Integer.parseInt(args[1]);
SearchCrawler crawler = new SearchCrawler(args[0], max, args[2]);
Thread search = new Thread(crawler);
System.out.println("Start searching...");
System.out.println("result:");
search.start();

}
}

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