Edit a XML file in java

Question

I have the following XML file:

<Tables>
    <table>
        <row></row>
    </table>
<Tables>

and I want to edit it to :

<Tables>
    <table>
        <row>some value</row>
    </table>
<Tables>

I write the XML file using file writer. How can I edit it?

What I was found that I create a temp file contains edits then delete the original file and rename the temp file. Is there any other way?

that's my code to write the file:

public boolean createTable(String path, String name, String[] properties) throws IOException {
    FileWriter writer = new FileWriter(path);
    writer.write("<Tables>");
    writer.write("\t<" + name + ">");
    for(int i=0; i<properties.length; i++){
        writer.write("\t\t<" + properties[0] + "></" + properties[0] + ">");
    }
    writer.write("\t</" + name + ">");
    writer.write("</Tables>");
    writer.close();
    return false;
}

Answer 1

Don't read and write XML yourself. Java comes with multiple API's for parsing and generating XML, which takes care of all the encoding and escaping issues for you:

• DOM XML is loaded into memory in a tree structure.
• SAX XML is processed as a sequence of events. This is a push-parser, where the parser calls your code for each event.
• StAX XML is read as a sequence of events/tokens. This is a pull-parser, where your code calls the parser to get next value.

You can also find many third-party libraries for parsing XML, and Java itself also supports marshalling of XML to POJO's.

In your case I'd suggest DOM, since it's easiest to use. Don't use DOM for huge XML files, since it loads the entire file into memory. For huge files, I'd suggest StAX.

Other than encoding issues, using an XML parser will make the code less susceptible to minor variations in the input, e.g. the 3 empty row elements below all mean the same. Or is the row element even empty, and how to get rid of existing content like shown:

<!-- row is empty -->
<row></row>
<row/>
<row />

<!-- row has content -->
<row>5 + 7 &lt; 10</row>
<row><![CDATA[5 + 7 < 10]]></row>
<row><condition expr="5 + 7 &lt; 10"></row>

Using DOM:

// Load XML from file
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder domBuilder = domFactory.newDocumentBuilder();
Document document = domBuilder.parse(file);

// Modify DOM tree (simple version)
NodeList rowNodes = document.getElementsByTagName("row");
for (int i = 0; i < rowNodes.getLength(); i++) {
    Node rowNode = rowNodes.item(i);

    // Remove existing content (if any)
    while (rowNode.getFirstChild() != null)
        rowNode.removeChild(rowNode.getFirstChild());

    // Add text content
    rowNode.appendChild(document.createTextNode("some value"));
}

// Save XML to file
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
transformer.transform(new DOMSource(document),
                      new StreamResult(file));

Answer 2

if your xml is static you can use this, here input.xml is your xml file

File file = new File("input.xml");
byte[] data;
try (FileInputStream fis = new FileInputStream(file)) {
   data = new byte[(int) file.length()];
    fis.read(data);
}
String input = new String(data, "UTF-8");
String tag = "<row>";
String newXML = input.substring(0, input.indexOf(tag) + tag.length()) + "your value" + input.substring(input.indexOf(tag) + tag.length(), input.length());
try (FileWriter fw = new FileWriter(file)) {
    fw.write(newXML);
}
System.out.println("XML Updated");