How do I insert a new node to an existing XML

Question

I would like to insert a new node into a existent xml file, but The code below inserts all the nodes again.

I do a test if the file exists. If not, I create a new xml file and write the tags. If exists, it also creates the nodes, but the wrong way.

//create a new file called "new.xml" in the SD card
File newxmlfile = new File(Environment.getExternalStorageDirectory() + "/download/teste/audit.xml");

if (newxmlfile.exists()){

    try{
        fileos = new FileOutputStream(newxmlfile, true);
    }catch(FileNotFoundException e){
        Log.e("FileNotFoundException", "can't create FileOutputStream");
    }


} else {                    

    try{
        newxmlfile.createNewFile();
    }catch(IOException e){
        Log.e("IOException", "exception in createNewFile() method");
    }

    try{
        fileos = new FileOutputStream(newxmlfile);
    }catch(FileNotFoundException e){
        Log.e("FileNotFoundException", "can't create FileOutputStream");
    }
}

//we create a XmlSerializer in order to write xml data
XmlSerializer serializer = Xml.newSerializer();
try {
    serializer.setOutput(fileos, "UTF-8");
    serializer.startDocument(null, Boolean.valueOf(true));
    serializer.setFeature("http://xmlpull.org/v1/doc/features.html#indent-output", true);

    serializer.startTag(null, "root");
        serializer.startTag(null, "child1");
        serializer.endTag(null, "child1");

        serializer.startTag(null, "child2");
        serializer.attribute(null, "attribute", "value");
        serializer.endTag(null, "child2");

            serializer.startTag(null, "child3");
        serializer.text("some text inside child3");
        serializer.endTag(null, "child3");                           
    serializer.endTag(null, "root");
    serializer.endDocument();
    serializer.flush();
    fileos.close();

    Context context = getApplicationContext();
    CharSequence text = "Save!";
    int duration = Toast.LENGTH_SHORT;
    Toast toast = Toast.makeText(context, text, duration);
    toast.show();

} catch (Exception e) {
    Log.e("Exception","error occurred while creating xml file");
}

The result is this:

<?xml version='1.0' encoding='UTF-8' standalone='yes' ?>
<root>
  <child1 />
  <child2 attribute="value" />
  <child3>some text inside child3</child3>
</root><?xml version='1.0' encoding='UTF-8' standalone='yes' ?>
<root>
  <child1 />
  <child2 attribute="value" />
  <child3>some text inside child3</child3>
</root>

But I want the result like this:

<?xml version='1.0' encoding='UTF-8' standalone='yes' ?>
<root>
  <child1 />
  <child2 attribute="value" />
  <child3>some text inside child3</child3>
  <child1 />
  <child2 attribute="value" />
  <child3>some text inside child3</child3>
</root>

Thanks!

Answer 1

Looks like there's not such API in Android. However, You still have the following options to fix the issue:

• Look for some open-source library which provides such ability;

• Do some manual string operations still using XmlSerializer, like provided below:

  private void testXMLFiles() {
      //create a new file called "new.xml" in the SD card
      final File newXmlFile = new File(Environment.getExternalStorageDirectory() + "/download/teste/audit.xml");
      RandomAccessFile randomAccessFile = null;
      final boolean fileExists = newXmlFile.exists();
      String lastLine = null;
  
      if (fileExists) {
          try {
              randomAccessFile = new RandomAccessFile(newXmlFile, "rw");
              randomAccessFile.seek(0);
  
              if (null != randomAccessFile) {
                  final Scanner scanner = new Scanner(newXmlFile);
                  int lastLineOffset = 0;
                  int lastLineLength = 0;
  
                  while (scanner.hasNextLine()) {
                      // +1 is for end line symbol
                      lastLine = scanner.nextLine();
                      lastLineLength = lastLine.length() + 2;
                      lastLineOffset += lastLineLength;
                  }
  
                  // don't need last </root> line offset
                  lastLineOffset -= lastLineLength;
  
                  // got to string before last
                  randomAccessFile.seek(lastLineOffset);
              }
          } catch(FileNotFoundException e) {
              Log.e("FileNotFoundException", "can't create FileOutputStream");
          } catch (IOException e) {
              Log.e("IOException", "Failed to find last line");
          }
      } else {
          try {
              newXmlFile.createNewFile();
          } catch(IOException e) {
              Log.e("IOException", "exception in createNewFile() method");
          }
  
          try {
              randomAccessFile = new RandomAccessFile(newXmlFile, "rw");
          } catch(FileNotFoundException e) {
              Log.e("FileNotFoundException", "can't create FileOutputStream");
          }
      }
  
      //we create a XmlSerializer in order to write xml data
      XmlSerializer serializer = Xml.newSerializer();
  
      if (randomAccessFile == null) {
          return;
      }
  
      try {
          final StringWriter writer = new StringWriter();
  
          serializer.setOutput(writer);
  
          if (!fileExists) {
              serializer.startDocument(null, true);
              serializer.setFeature("http://xmlpull.org/v1/doc/features.html#indent-output", true);
              serializer.startTag(null, "root");
          } else {
              serializer.setFeature("http://xmlpull.org/v1/doc/features.html#indent-output", true);
          }
  
          serializer.startTag(null, "child1");
          serializer.endTag(null, "child1");
  
          serializer.startTag(null, "child2");
          serializer.attribute(null, "attribute", "value");
          serializer.endTag(null, "child2");
  
          serializer.startTag(null, "child3");
          serializer.text("some text inside child3");
          serializer.endTag(null, "child3");
  
          if (!fileExists) {
              serializer.endTag(null, "root");
          }
  
          serializer.flush();
  
          if (lastLine != null) {
              serializer.endDocument();
              writer.append(lastLine);
          }
  
          // Add \n just for better output in console
          randomAccessFile.writeBytes(writer.toString() + "\n");
          randomAccessFile.close();
  
          Toast.makeText(getApplicationContext(), "Save!", Toast.LENGTH_SHORT).show();
      } catch (Exception e) {
          Log.e("Exception","error occurred while creating xml file");
          e.printStackTrace();
      }
  }
  

Its output after second run is the following (quite similar to what You expect):

<?xml version='1.0' standalone='yes' ?>
<root>
  <child1 />
  <child2 attribute="value" />
  <child3>some text inside child3</child3>

<child1 />
<child2 attribute="value" />
<child3>some text inside child3</child3></root>

• Store all tags from initial xml (e.g. using SAXParser you can read tags, write to new file the same time and apppend new ones at the end using XMLSerializer);