Java中怎么实现一个网络爬虫

Java中怎么实现一个网络爬虫，针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。

首先介绍每个类的功能：

DownloadPage.java的功能是下载此超链接的页面源代码.

FunctionUtils.java 的功能是提供不同的静态方法，包括：页面链接正则表达式匹配,获取URL链接的元素,判断是否创建文件,获取页面的Url并将其转换为规范的Url,截取网页网页源文件的目标内容。

HrefOfPage.java 的功能是获取页面源代码的超链接。

UrlDataHanding.java 的功能是整合各个给类，实现url到获取数据到数据处理类。

UrlQueue.java 的未访问Url队列。

VisitedUrlQueue.java 已访问过的URL队列。

下面介绍一下每个类的源代码：

DownloadPage.java 此类要用到HttpClient组件。

View Code    package com.sreach.spider;      import java.io.IOException;   import org.apache.http.HttpEntity;   import org.apache.http.HttpResponse;   import org.apache.http.client.ClientProtocolException;   import org.apache.http.client.HttpClient;   import org.apache.http.client.methods.HttpGet;   import org.apache.http.impl.client.DefaultHttpClient;   import org.apache.http.util.EntityUtils;      public class DownloadPage   {                public static String getContentFormUrl(String url)       {                     HttpClient client = new DefaultHttpClient();           HttpGet getHttp = new HttpGet(url);              String content = null;              HttpResponse response;           try          {                             response = client.execute(getHttp);               HttpEntity entity = response.getEntity();                  VisitedUrlQueue.addElem(url);                  if (entity != null)               {                                     content = EntityUtils.toString(entity);                                        if (FunctionUtils.isCreateFile(url)                           && FunctionUtils.isHasGoalContent(content) != -1)                   {                       FunctionUtils.createFile(FunctionUtils                               .getGoalContent(content), url);                   }               }              } catch (ClientProtocolException e)           {               e.printStackTrace();           } catch (IOException e)           {               e.printStackTrace();           } finally          {               client.getConnectionManager().shutdown();           }                      return content;       }      }

FunctionUtils.java 此类的方法均为static方法

View Code    package com.sreach.spider;   import java.io.BufferedWriter;  import java.io.File;  import java.io.FileOutputStream;  import java.io.IOException;  import java.io.OutputStreamWriter;  import java.util.regex.Matcher;  import java.util.regex.Pattern;   public class FunctionUtils  {            private static String pat = "http://www\\.oschina\\.net/code/explore/.*/\\w+\\.[a-zA-Z]+";      private static Pattern pattern = Pattern.compile(pat);       private static BufferedWriter writer = null;            public static int depth = 0;            public static String[] divUrl(String url)      {          return url.split("/");      }            public static boolean isCreateFile(String url)      {          Matcher matcher = pattern.matcher(url);           return matcher.matches();      }            public static void createFile(String content, String urlPath)      {                   String[] elems = divUrl(urlPath);          StringBuffer path = new StringBuffer();           File file = null;          for (int i = 1; i < elems.length; i++)          {              if (i != elems.length - 1)              {                   path.append(elems[i]);                  path.append(File.separator);                  file = new File("D:" + File.separator + path.toString());               }               if (i == elems.length - 1)              {                  Pattern pattern = Pattern.compile("\\w+\\.[a-zA-Z]+");                  Matcher matcher = pattern.matcher(elems[i]);                  if ((matcher.matches()))                  {                      if (!file.exists())                      {                          file.mkdirs();                      }                      String[] fileName = elems[i].split("\\.");                      file = new File("D:" + File.separator + path.toString()                              + File.separator + fileName[0] + ".txt");                      try                     {                          file.createNewFile();                          writer = new BufferedWriter(new OutputStreamWriter(                                  new FileOutputStream(file)));                          writer.write(content);                          writer.flush();                          writer.close();                          System.out.println("创建文件成功");                      } catch (IOException e)                      {                          e.printStackTrace();                      }                   }              }           }      }            public static String getHrefOfInOut(String href)      {                   String resultHref = null;                    if (href.startsWith("http://"))          {              resultHref = href;          } else         {                           if (href.startsWith("/"))              {                  resultHref = "http://www.oschina.net" + href;              }          }           return resultHref;      }            public static String getGoalContent(String content)      {          int sign = content.indexOf("<pre class=\"");          String signContent = content.substring(sign);           int start = signContent.indexOf(">");          int end = signContent.indexOf("</pre>");           return signContent.substring(start + 1, end);      }            public static int isHasGoalContent(String content)      {          return content.indexOf("<pre class=\"");      }   }

HrefOfPage.java 此类为获取页面的超链接

View Code    package com.sreach.spider;   public class HrefOfPage  {           public static void getHrefOfContent(String content)      {          System.out.println("开始");          String[] contents = content.split("<a href=\"");          for (int i = 1; i < contents.length; i++)          {              int endHref = contents[i].indexOf("\"");               String aHref = FunctionUtils.getHrefOfInOut(contents[i].substring(  , endHref));               if (aHref != null)              {                  String href = FunctionUtils.getHrefOfInOut(aHref);                   if (!UrlQueue.isContains(href)                          && href.indexOf("/code/explore") != -1                         && !VisitedUrlQueue.isContains(href))                  {                      UrlQueue.addElem(href);                  }              }          }           System.out.println(UrlQueue.size() + "--抓取到的连接数");          System.out.println(VisitedUrlQueue.size() + "--已处理的页面数");       }   }

UrlDataHanding.java 此类主要是从未访问队列中获取url,下载页面，分析url，保存已访问url等操作，实现Runnable接口

View Code    package com.sreach.spider;   public class UrlDataHanding implements Runnable  {           public void dataHanding(String url)      {              HrefOfPage.getHrefOfContent(DownloadPage.getContentFormUrl(url));      }                public void run()      {          while(!UrlQueue.isEmpty())          {             dataHanding(UrlQueue.outElem());          }      }  }

UrlQueue.java 此类主要是用来存放未访问的URL队列

View Code    package com.sreach.spider;   import java.util.LinkedList;   public class UrlQueue  {           public static LinkedList<String> urlQueue = new LinkedList<String>();                 public static final int MAX_SIZE = 10000;            public synchronized static void addElem(String url)      {          urlQueue.add(url);      }            public synchronized static String outElem()      {          return urlQueue.removeFirst();      }            public synchronized static boolean isEmpty()      {          return urlQueue.isEmpty();      }            public  static int size()      {          return urlQueue.size();      }            public  static boolean isContains(String url)      {          return urlQueue.contains(url);      }   }

VisitedUrlQueue.java 主要是保存已访问过的URL，使用HashSet来保存，主要是考虑到每个访问过的URL是不同。HashSet刚好符合这个要求

View Code    package com.sreach.spider;   import java.util.HashSet;    public class VisitedUrlQueue  {      public static HashSet<String> visitedUrlQueue = new HashSet<String>();       public synchronized static void addElem(String url)      {          visitedUrlQueue.add(url);      }       public synchronized static boolean isContains(String url)      {          return visitedUrlQueue.contains(url);      }       public synchronized static int size()      {          return visitedUrlQueue.size();      }  }

Test.java 此类为测试类

View Code    import java.sql.SQLException;   import com.sreach.spider.UrlDataHanding;  import com.sreach.spider.UrlQueue;   public class Test  {    public static void main(String[] args) throws SQLException    {        String url = "http://www.oschina.net/code/explore/achartengine/client/AndroidManifest.xml";        String url1 = "http://www.oschina.net/code/explore";        String url2 = "http://www.oschina.net/code/explore/achartengine";        String url3 = "http://www.oschina.net/code/explore/achartengine/client";                        UrlQueue.addElem(url);        UrlQueue.addElem(url1);        UrlQueue.addElem(url2);        UrlQueue.addElem(url3);                UrlDataHanding[] url_Handings = new UrlDataHanding[10];                    for(int i = 0 ; i < 10 ; i++)            {                url_Handings[i] = new UrlDataHanding();                new Thread(url_Handings[i]).start();            }     }  }

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