一个Java Web搜索程序

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 http://127.0.0.1:8080/zz3zcwbwebhome/index.jsp 20 java 

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

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