Add new attributes to an existing XML node in java?

Question

I want to add an attribute to an existing xml node.I don't want to add new elements (new nodes) to my xml file, I just want to add a new attribute. How can I do this?

In particular I've tried this lines of code:

Element process = doc.getElementsById("id");
    process.setAttribute("modelgroup", "");

TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(new  File("C:\\Users\\Blerta\\workspaceKEPLER\\XML_to_JSON\\SampleExample.xml"));
transformer.transform(source, result);

But I get the following exception:

Exception in thread "main" java.lang.NullPointerException
    at Main.appendAttributes(Main.java:172)
    at Main.displayNodes(Main.java:65)
    at Main.displayNodes(Main.java:138)
    at Main.main(Main.java:42)**

paste the line where nullpointer occures – Łukasz Rzeszotarski Nov 18 '13 at 16:50 — Łukasz Rzeszotarski, Nov 18 '13 at 16:50

score 29 · Accepted Answer · edited May 12 '17 at 07:29

29

in DOM parser it is very easy. get your node and simply use this function.

((Element)node).setAttribute("attr_name","attr_value");

then finally update your document. like this..

        Transformer transformer = TransformerFactory.newInstance().newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty(OutputKeys.METHOD, "xml");
        transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "5");
        DOMSource source = new DOMSource(document);
        StreamResult result = new StreamResult(new File(tablePath));
        transformer.transform(source, result);

edited May 12 '17 at 07:29

payam_sbr

1,428
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answered Nov 18 '13 at 16:37

subash

3,116
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I've allready tried this but I cannot apply setAttribute to the node – user2966458 Nov 18 '13 at 16:40
2

**doc.getElementsByTagName("process");** it is return NodeList. try like this. **NodeList list = doc.getElementsByTagName("process");**. Element el = (Element)list.item(0); then you can use el.setAttribute("attr_name","attr_val"); – subash Nov 18 '13 at 16:49
What if node isn't castable to Element? – Stephan Jun 29 '17 at 15:16

score 8 · Answer 2 · answered Dec 10 '14 at 03:06

8

The easiest and the shortest is to cast the node to org.w3c.dom.Element and then invoke setAttribute on it:

((Element)aNode).setAttribute("name", "value");

answered Dec 10 '14 at 03:06

Sergey Tarasov

858
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What if node isn't castable to Element? – Stephan Jun 29 '17 at 15:16
Yes, what if aNode does not extend Element class? – Renat Gatin Oct 25 '17 at 23:42
3

@Stephan, it doesn't make sense to add an attribute to something that isn't an Element. – Dawood ibn Kareem Oct 30 '17 at 23:48
1

@DawoodibnKareem An exception will be raised if `aNode` isn't castable to Element. – Stephan Oct 31 '17 at 07:12
2

Well, yes, obviously. That's exactly what SHOULD happen, because adding an attribute to something that's not an Element makes no sense. – Dawood ibn Kareem Oct 31 '17 at 07:20

score 3 · Answer 3 · answered Nov 18 '13 at 16:46

You could do it in a few lines using xslt. Oracle have a half decent tutorial with all the code snippets http://docs.oracle.com/javase/tutorial/jaxp/xslt/transformingXML.html

The key bit for your xslt would be something like the following:

    <xsl:template match="elementToAddNewAttrTo">
        <xsl:attribute name="newAttrName">NewAttrValue</xsl:attribute>
    </xsl:template>

score 1 · Answer 4 · answered Aug 13 '17 at 20:48

Recommended approach:

Node node = ...;
if(node.getNodeType() == Node.ELEMENT_NODE)
{
    ((Element) node).setAttribute("name", "value");
}

Situational approach:

try
{
    // ...
    Node node = ...;
    ((Element) node).setAttribute("name", "value");
    // ...
}
catch(ClassCastException e)
{
    // Handle exception
}

Only use the try-catch approach if you already know that all the nodes that you process should be of type 'Element' (and thus any other case is an "exception" and should break from the code).

Add new attributes to an existing XML node in java?

4 Answers4

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