如何在map/reduce作业上只输出一次标题作为配置单元导入的csv，而不是手动输入列名。
公共类mymapper扩展了mapper{

public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
    try {
        InputStream is = new ByteArrayInputStream(value.toString().getBytes());
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc = dBuilder.parse(is);
        //....

        doc.getDocumentElement().normalize();

        // .......
        //context.write(new Text("el_from \t Title \t External Link"), NullWritable.get());
        // .... 
                String title = eElement.getElementsByTagName("title").item(0).getTextContent();
                text = eElement.getElementsByTagName("text").item(0).getTextContent();
                String id = eElement.getElementsByTagName("id").item(0).getTextContent(); 
                 for(int j = 0; j <  externalLinks.length; j++)
                 {
                     Pattern prl = Pattern.compile("(http:\\/\\/www\\.|https:\\/\\/www\\.|http:\\/\\/|https:\\/\\/)?[a-z0-9]+([\\-\\.]{1}[a-z0-9]+)*\\.[a-z]{2,5}(:[0-9]{1,5})?");
                     Matcher ml = prl.matcher(externalLinks[j]);
                     if(ml.find()) {
                         MatchResult mlr = ml.toMatchResult();
                         context.write(new Text(id+","+title + ","+ mlr.group(0)), NullWritable.get());
                     }                       
                 }
            }
        }
    } catch (Exception e) {
        // LogWriter.getInstance().WriteLog(e.getMessage());
    }
    }
    }`enter code here`

我得到的结果是这样的
3，阿格里科图拉，http://www.treccani.it
3，阿格里科图拉，http://www.wwf.it/client/render.aspx
我想要的结果就像下面的标题
id、标题、链接
3，阿格里科图拉，http://www.treccani.it
3，阿格里科图拉，http://www.wwf.it/client/render.aspx