1. Read into the relevant node.
2. Update the text content.
3. Save it back to XML.

Suppose that I have the following XML and I want to update the text of Value node when the OntologyCat is 2.

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<RuleSet>
     <Rule>
          <OntologyCat>0</OntologyCat>
          <OntologyCatName>Status</OntologyCatName>
          <Value>Online</Value>
     </Rule>
     <Rule>
          <OntologyCat>1</OntologyCat>
          <OntologyCatName>Act</OntologyCatName>
          <Value>false</Value>
     </Rule>
     <Rule>
          <OntologyCat>2</OntologyCat>
          <OntologyCatName>Width</OntologyCatName>
          <Value>OldValue</Value>
     </Rule>
</RuleSet>

The complete code I have separated into three methods, which explains three key points above.

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.StringWriter;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

// This class shows you that how to update a XML in Java
public class UpdateXML {

     // Save the updated DOM into the XML back
     private void saveToXML(File file, Document doc) {
          try {
               TransformerFactory factory = TransformerFactory.newInstance();
               Transformer transformer = factory.newTransformer();
               transformer.setOutputProperty(OutputKeys.INDENT, "yes");

               StringWriter writer = new StringWriter();
               StreamResult result = new StreamResult(writer);
               DOMSource source = new DOMSource(doc);

               transformer.transform(source, result);

               String strTemp = writer.toString();

               FileWriter fileWriter = new FileWriter(file);
               BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);

               bufferedWriter.write(strTemp);
               bufferedWriter.flush();
               bufferedWriter.close();
          }
          catch(Exception ex) {
          }
     }

     // Read into the relevant node and update the text value
     private void updateTextValue(Document doc, String oldValue, String newValue) {
          try {
               Element root = doc.getDocumentElement();

               // Return the NodeList on a given tag name
               NodeList childNodes = root.getElementsByTagName("Rule");

               for(int index = 0; index < childNodes.getLength(); index++) {
                    NodeList subChildNodes = childNodes.item(index).getChildNodes();
                    if(subChildNodes.item(1).getTextContent().equals(oldValue)) {
                         // Update the relevant node text content. item() position the NodeList.
                         subChildNodes.item(5).setTextContent(newValue);
                    }
               }
          }
          catch(Exception ex) {
          }
     }

     private void updateXML(File file, String strOldValue, String strNewValue) {
          DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();

          try {
               // Convert CDATA nodes to Text node append
               docFactory.setCoalescing(true);

               DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
               Document doc = docBuilder.parse(file);

               updateTextValue(doc, strOldValue, strNewValue);
               saveToXML(file, doc);
          }
          catch(Exception ex) {
          }
     }

     public static void main(String[] args) {
          File file = new File("c:\\doc.xml");
          new UpdateXML().updateXML(file, "2", "NewValueToUpdate");
     }
}

) throws IOException{
		
		FileWriterExample fileWriter = new FileWriterExample();
		fileWriter.write();
		fileWriter.writeThruBuffer();
	}
	
	private void write() throws IOException{
		Writer fileWriter = null;
		try {
			long startTime = System.currentTimeMillis();
			fileWriter = new FileWriter(new File("FileWriterExample.dat"));
			for(int i=1000000; i>0; i--){
				fileWriter.write(i+" ,");
			}
			System.out.println("Time Taken with out buffer : "+
					(System.currentTimeMillis() - startTime));
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		finally{
			if(null != fileWriter){
				fileWriter.close();
			}
		}
	}
	
	private void writeThruBuffer() throws IOException{
		Writer fileWriter = null;
		try {
			long startTime = System.currentTimeMillis();
			fileWriter = new BufferedWriter(new FileWriter(new 
					File("BufferedFileWriterExample.dat")));
			
			for(int i=1000000; i>0; i--){
				fileWriter.write(i+" ,");
			}
			System.out.println("Time Taken with buffer : "+
					(System.currentTimeMillis() - startTime));
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		finally{
			if(null != fileWriter){
				fileWriter.close();
			}
		}
	}
}

Console output
————–
/local/opt/java org.sanju.FileWriterExample
Time Taken with out buffer : 640
Time Taken with buffer : 529

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class FileWriterDemo {
	public static void main(String args[]){
		try {

			// change filePath  as Desired.
			String filePath = "D:\\java.txt";

			//Create a new FileWriter Object
			FileWriter writer = new FileWriter(new File(filePath));

			// Writing to file. Can be String, Char, Char Array
			writer.write("This is a test File for demonstrate FileWriter. ");

			//terminate Filewriter
			writer.close();

		} catch (IOException e) {
			// Catch errors
			System.out.println(e.getMessage());
		}

	}
}

Classse

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class GravaArquivo {
    public void novoArquivo(String nomeArquivo, String texto) {
        try {
            BufferedWriter out = new BufferedWriter(new FileWriter(“nomeArquivo”));
            out.write(texto);
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Utilização

Para utilizar a classe é bem simples, basta instanciar a classe e utilizar o método novoArquivo.

private GravaArquivo arquivo;
arquivo = new GravaArquivo();
arquivo.novoArquivo(“c:\\arquivo.txt”, “testeeeee”);

flw