Java写的爬虫的基本程序

精选转载

Eric_2007 2009-03-12 19:16:27

这是一个web搜索的基本程序，从命令行输入搜索条件（起始的URL、处理url的最大数、要搜索的字符串),
它就会逐个对Internet上的URL进行实时搜索,查找并输出匹配搜索条件的页面。这个程序的原型来自《java编程艺术》，
为了更好的分析，站长去掉了其中的GUI部分，并稍作修改以适用jdk1.5。以这个程序为基础，可以写出在互联网上搜索
诸如图像、邮件、网页下载之类的“爬虫”。
先请看程序运行的过程：

D:\java>javac SearchCrawler.java（编译）

D:\java>java   SearchCrawler [url]http://127.0.0.1:8080/zz3zcwbwebhome/index.jsp[/url] 20 java

Start searching...
result:
searchString=java
[url]http://127.0.0.1:8080/zz3zcwbwebhome/index.jsp[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/reply.jsp[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/learn.jsp[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/download.jsp[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/article.jsp[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/myexample/jlGUIOverview.htm[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/myexample/Proxooldoc/index.html[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=301[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=297[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=291[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=286[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=285[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=284[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=276[/url]
[url]http://127.0.0.1:8080/zz3zcwbwebhome/view.jsp?id=272  [/url]

又如：
D:\java>java    SearchCrawler [url]http://www.sina.com [/url] 20 java
Start searching...
result:
searchString=java
[url]http://sina.com[/url]
[url]http://redirect.sina.com/WWW/sinaCN/www.sina.com.cn[/url] class=a2
[url]http://redirect.sina.com/WWW/sinaCN/www.sina.com.cn[/url] class=a8
[url]http://redirect.sina.com/WWW/sinaHK/www.sina.com.hk[/url] class=a2
[url]http://redirect.sina.com/WWW/sinaTW/www.sina.com.tw[/url] class=a8
[url]http://redirect.sina.com/WWW/sinaUS/home.sina.com[/url] class=a8
[url]http://redirect.sina.com/WWW/smsCN/sms.sina.com.cn/[/url] class=a2
[url]http://redirect.sina.com/WWW/smsCN/sms.sina.com.cn/[/url] class=a3
[url]http://redirect.sina.com/WWW/sinaNet/www.sina.net/[/url] class=a3

D:\java>
下面是这个程序的源码

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

// 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 [url]http://somehost.com/[/url]
     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();

    }
}