nutch源码阅读(3)-Injector的Mapper

最新推荐文章于 2016-10-10 17:29:04 发布

原创最新推荐文章于 2016-10-10 17:29:04 发布 · 114 阅读

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本文深入探讨了Mapper组件在处理文本数据时的运行逻辑，包括如何解析包含元数据和分数的URL，对其进行规范化和过滤，并收集处理后的数据。重点介绍了如何识别并处理特定的元数据字段，如自定义分数和抓取间隔，以及如何将这些信息整合到CrawlDatum对象中，用于后续的抓取任务。

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上篇看到Injector的初始化，这次继续阅读，看看Mapper

public void map(WritableComparable key, Text value,
                    OutputCollector<Text, CrawlDatum> output, Reporter reporter)
      throws IOException {
      String url = value.toString();              // value is line of text
      //忽略开头符号为#的
      if (url != null && url.trim().startsWith("#")) {
          /* Ignore line that start with # */
          return;
      }

      // if tabs : metadata that could be stored
      // must be name=value and separated by \t
      float customScore = -1f;
      int customInterval = interval;
      int fixedInterval = -1;
      Map<String,String> metadata = new TreeMap<String,String>();
      //对文本进行拆分
      if (url.indexOf("\t")!=-1){
    	  String[] splits = url.split("\t");
    	  url = splits[0];
    	  for (int s=1;s<splits.length;s++){
    		  // find separation between name and value
    		  int indexEquals = splits[s].indexOf("=");
    		  if (indexEquals==-1) {
    			  // skip anything without a =
    			  continue;		    
    		  }
                  //得到元数据名称及值
    		  String metaname = splits[s].substring(0, indexEquals);
    		  String metavalue = splits[s].substring(indexEquals+1);
                  //判断是不是保留的元数据名称
    		  if (metaname.equals(nutchScoreMDName)) {
    			  try {
    			  customScore = Float.parseFloat(metavalue);}
    			  catch (NumberFormatException nfe){}
    		  }
                  else if (metaname.equals(nutchFetchIntervalMDName)) {
                          try {
                                  customInterval = Integer.parseInt(metavalue);}
                          catch (NumberFormatException nfe){}
                  }
                  else if (metaname.equals(nutchFixedFetchIntervalMDName)) {
                          try {
                                  fixedInterval = Integer.parseInt(metavalue);}
                          catch (NumberFormatException nfe){}
                  }
                  //不是就保存到容器中
    		  else metadata.put(metaname,metavalue);
    	  }
      }
      try {
       //对url规范化，过滤
        url = urlNormalizers.normalize(url, URLNormalizers.SCOPE_INJECT);
        url = filters.filter(url);             // filter the url
      } catch (Exception e) {
        if (LOG.isWarnEnabled()) { LOG.warn("Skipping " +url+":"+e); }
        url = null;
      }
      if (url == null) {
        reporter.getCounter("injector", "urls_filtered").increment(1);
      } else {                                   // if it passes
        value.set(url);                           // collect it
        //创建一个CrawlDatum，用来保存所处阶段，元数据，分值，计数等信息
        CrawlDatum datum = new CrawlDatum();
        datum.setStatus(CrawlDatum.STATUS_INJECTED);

        // Is interval custom? Then set as meta data
        if (fixedInterval > -1) {
          // Set writable using float. Flaot is used by AdaptiveFetchSchedule
          datum.getMetaData().put(Nutch.WRITABLE_FIXED_INTERVAL_KEY, new FloatWritable(fixedInterval));
          datum.setFetchInterval(fixedInterval);
        } else {
          datum.setFetchInterval(customInterval);
        }

        datum.setFetchTime(curTime);
        // now add the metadata
        Iterator<String> keysIter = metadata.keySet().iterator();
        while (keysIter.hasNext()){
        	String keymd = keysIter.next();
        	String valuemd = metadata.get(keymd);
        	datum.getMetaData().put(new Text(keymd), new Text(valuemd));
        }
        if (customScore != -1) datum.setScore(customScore);
        else datum.setScore(scoreInjected);
        try {
               //分值初始化
        	scfilters.injectedScore(value, datum);
        } catch (ScoringFilterException e) {
        	if (LOG.isWarnEnabled()) {
        		LOG.warn("Cannot filter injected score for url " + url
        				+ ", using default (" + e.getMessage() + ")");
        	}
        }
        reporter.getCounter("injector", "urls_injected").increment(1);
        output.collect(value, datum);
      }
    }
  }