简单的网络爬虫

import java.util.*;
import java.net.*;
import java.io.*;
import java.util.regex.*;
// 搜索Web爬行者

public class SearchCrawler extends Thread{
  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;
  }

  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("DOCTYPE \\s+ PUBLIC",Pattern.CASE_INSENSITIVE);

    //Matcher m = p.matcher(pageContents);


    ArrayList< String> linkList = new ArrayList< String>();
   // while (m.find()) {

    int no=0;
    while(true){
      no = pageContents.indexOf("href=", no);
      if(no<=0) break;
      int startno=pageContents.indexOf("\"", no);
      int stopno = pageContents.indexOf("\"", startno+1);
      //String link = m.group(0);

      no++;
      String link = pageContents.substring(startno+1, stopno);
      if (link.length() < 1) {
        continue;
      }
      //跳过css

      if (link.endsWith(".css")){
         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() + 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() + 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.



      // 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("",10,".NET");
    System.out.println("Start searching...");
    System.out.println("result:");
    crawler.start();
  }
}