创建一个xml文件并将一个新节点插入此XML

Question

我试图创建一个xml文件，然后稍后在

上添加一些节点。

我已经成功创建了xml文件，但是添加新节点是一个问题

我正在使用此代码创建xml

try {

    String out = "userData.xml";
        FileOutputStream fos = new  FileOutputStream(out);
        //FileOutputStream fileos= mcontext.openFileOutput(fos, Context.MODE_PRIVATE);
        FileOutputStream fileos = new FileOutputStream (new File(out), true); // true will be same as Context.MODE_APPEND
        XmlSerializer xmlSerializer = Xml.newSerializer();
        StringWriter writer = new StringWriter();
        xmlSerializer.setOutput(writer);
        xmlSerializer.startDocument("UTF-8", true);
        xmlSerializer.startTag(null, "userData");
        xmlSerializer.startTag(null, "userName");
        xmlSerializer.text("testting");
        xmlSerializer.endTag(null, "userName");
        xmlSerializer.startTag(null,"password");
        xmlSerializer.text("paswordtesting");
        xmlSerializer.endTag(null, "password");
        xmlSerializer.endTag(null, "userData");
        xmlSerializer.endDocument();
        xmlSerializer.flush();
        String dataWrite = writer.toString();
        fileos.write(dataWrite.getBytes());
        fileos.close();
    }
catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    Toast.makeText(mcontext, "IllegalStateException" + e, Toast.LENGTH_SHORT).show();
    }
catch (IllegalArgumentException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    }
catch (IllegalStateException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    Toast.makeText(mcontext, "IllegalStateException", Toast.LENGTH_SHORT).show();
    }
catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    Toast.makeText(mcontext, "IOException", Toast.LENGTH_SHORT).show();
    }
    }

创建一个像这样的xml文件

    <?xml version='1.0' encoding='UTF-8' standalone='yes' ?>
<userData>
<userName>testting</userName>
<password>paswordtesting</password>
</userData>

现在我要向该xml文件添加新节点 使用此代码

public void testXMLFiles(Context mContext) {
        //create a new file called "new.xml" in the SD card
        final File newXmlFile = new File("userData.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, "userData");
            } 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, "userData");
            }

            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(mContext, "Save!", Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            Log.e("Exception","error occurred while creating xml file");
            e.printStackTrace();
        }
    }

我得到的投入是

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

我想要的是

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

如何获得正确的投放位置