Question

我想在现有的xml文件中插入一个新节点，但下面的代码会再次插入所有节点。

如果文件存在，我会进行测试。如果没有，我创建一个新的xml文件并编写标签。如果存在，它也会创建节点，但方法错误。

//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");
}

结果如下：

<?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>

但我希望结果如下：

<?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>

谢谢！

Answer 1

看起来Android中没有这样的API。但是，您仍有以下选项可以解决此问题：

寻找一些提供这种能力的开源库;

仍然使用XmlSerializer进行一些手动字符串操作，如下所示：

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();
    }
}

第二次运行后的输出如下（非常类似于您的预期）：

<?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>

存储来自初始xml的所有代码（例如，使用SAXParser您可以读取代码，同时写入新文件并使用XMLSerializer）在最后添加新文件;

如何将新节点插入现有XML

1 个答案: