setNumMappersDynamically

private static void setNumMappers(int numNodes) {
        String mapred_side_xml_path = "/opt/hadoop-2.3.0-cdh5.0.1/etc/hadoop/mapred-site.xml";
        try {
            DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
            domFactory.setIgnoringComments(true);
            DocumentBuilder builder = domFactory.newDocumentBuilder();
            Document doc = builder.parse(new File(mapred_side_xml_path));

            NodeList nodes = doc.getElementsByTagName("configuration");

            Text n = doc.createTextNode("mapreduce.job.running.map.limit");
            Element name = doc.createElement("name");
            name.appendChild(n);

            Text v = doc.createTextNode(String.valueOf(numNodes));
            Element value = doc.createElement("value");
            value.appendChild(v);

            Element property = doc.createElement("property");
            property.appendChild(name);
            property.appendChild(value);

            nodes.item(0).appendChild(property);

            Transformer transformer = TransformerFactory.newInstance().newTransformer();
            transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
            transformer.setOutputProperty(OutputKeys.METHOD, "xml");
            transformer.setOutputProperty(OutputKeys.INDENT, "yes");
            transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
            transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");

            Result output = new StreamResult(new File(mapred_side_xml_path));
            Source input = new DOMSource(doc);
            transformer.transform(input, output);

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (TransformerException e) {
            e.printStackTrace();
        }
    }