怎么配置Nutch模拟浏览器绕过反爬虫限制

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当我们配置Nutch抓取 http://yangshangchuan.iteye.com 的时候，抓取的所有页面内容均为：您的访问请求被拒绝 ...... 这是最简单的反爬虫策略（该策略简单地读取HTTP请求头User-Agent的值来判断是人（浏览器）还是机器爬虫），我们只需要简单地配置Nutch来模拟浏览器（simulate web browser）就可以绕过这种限制。

在nutch-default.xml中有5项配置是和User-Agent相关的：

  http.agent.description    Further description of our bot- this text is used in  the User-Agent header.  It appears in parenthesis after the agent name.    http.agent.url    A URL to advertise in the User-Agent header.  This will    appear in parenthesis after the agent name. Custom dictates that this   should be a URL of a page explaining the purpose and behavior of this   crawler.    http.agent.email    An email address to advertise in the HTTP 'From' request   header and User-Agent header. A good practice is to mangle this   address (e.g. 'info at example dot com') to avoid spamming.    http.agent.name    HTTP 'User-Agent' request header. MUST NOT be empty -   please set this to a single word uniquely related to your organization.  NOTE: You should also check other related properties:        http.robots.agents        http.agent.description        http.agent.url        http.agent.email        http.agent.version  and set their values appropriately.    http.agent.version  Nutch-1.7  A version string to advertise in the User-Agent    header.

在类nutch2.7/src/plugin/lib-http/src/java/org/apache/nutch/protocol/http/api/HttpBase.java中可以看到这5项配置是如何构成User-Agent的：

this.userAgent = getAgentString( conf.get("http.agent.name"),         conf.get("http.agent.version"),         conf.get("http.agent.description"),         conf.get("http.agent.url"),         conf.get("http.agent.email") );

  private static String getAgentString(String agentName,                                       String agentVersion,                                       String agentDesc,                                       String agentURL,                                       String agentEmail) {        if ( (agentName == null) || (agentName.trim().length() == 0) ) {      // TODO : NUTCH-258      if (LOGGER.isErrorEnabled()) {        LOGGER.error("No User-Agent string set (http.agent.name)!");      }    }        StringBuffer buf= new StringBuffer();        buf.append(agentName);    if (agentVersion != null) {      buf.append("/");      buf.append(agentVersion);    }    if ( ((agentDesc != null) && (agentDesc.length() != 0))    || ((agentEmail != null) && (agentEmail.length() != 0))    || ((agentURL != null) && (agentURL.length() != 0)) ) {      buf.append(" (");            if ((agentDesc != null) && (agentDesc.length() != 0)) {        buf.append(agentDesc);        if ( (agentURL != null) || (agentEmail != null) )          buf.append("; ");      }            if ((agentURL != null) && (agentURL.length() != 0)) {        buf.append(agentURL);        if (agentEmail != null)          buf.append("; ");      }            if ((agentEmail != null) && (agentEmail.length() != 0))        buf.append(agentEmail);            buf.append(")");    }    return buf.toString();  }

在类nutch2.7/src/plugin/protocol-http/src/java/org/apache/nutch/protocol/http/HttpResponse.java中使用User-Agent请求头，这里的http.getUserAgent()返回的userAgent就是HttpBase.java中的userAgent：

String userAgent = http.getUserAgent();if ((userAgent == null) || (userAgent.length() == 0)) {        if (Http.LOG.isErrorEnabled()) { Http.LOG.error("User-agent is not set!"); }} else {        reqStr.append("User-Agent: ");        reqStr.append(userAgent);        reqStr.append("\r\n");}

通过上面的分析可知：在nutch-site.xml中只需要增加如下几种配置之一便可以模拟一个特定的浏览器（Imitating a specific browser）：

1、模拟Firefox浏览器：

        http.agent.name        Mozilla/5.0 (Windows NT 6.1; WOW64; rv:27.0) Gecko        http.agent.version        20100101 Firefox/27.0

2、模拟IE浏览器：

        http.agent.name        Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident        http.agent.version        6.0)

3、模拟Chrome浏览器：

        http.agent.name        Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Safari        http.agent.version        537.36

4、模拟Safari浏览器：

        http.agent.name        Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version/5.1.7 Safari        http.agent.version        534.57.2

5、模拟Opera浏览器：

        http.agent.name        Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1700.102 Safari/537.36 OPR        http.agent.version        19.0.1326.59

后记：查看User-Agent的方法：

1、http://www.useragentstring.com

2、http://whatsmyuseragent.com

3、http://www.enhanceie.com/ua.aspx

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