Introduction to the 'org.w3c.dom.DOMException: Only one root element allowed' Exception

When working with XML documents in Java using the DOM (Document Object Model), you may come across the 'org.w3c.dom.DOMException: Only one root element allowed' exception. This exception occurs when you try to create an XML document that has more than one root element.

What is a Root Element?

In an XML document, the root element is the top-level element that contains all the other elements. It is the first element in the document and is the starting point for any XML parser. Only one root element is allowed per XML document.

What Causes the 'org.w3c.dom.DOMException: Only one root element allowed' Exception?

When you try to create an XML document with more than one root element, the DOM parser will throw the 'org.w3c.dom.DOMException: Only one root element allowed' exception. This can occur for several reasons:

• You may have accidentally added multiple root elements to your XML document.
• Your XML document may have been corrupted or improperly formatted.
• You may be using an XML schema or DTD (Document Type Definition) that only allows for one root element.

How to Fix the 'org.w3c.dom.DOMException: Only one root element allowed' Exception

To fix this exception, you need to ensure that your XML document has only one root element. You can do this by checking your code to make sure that you are only creating one root element, or by correcting any formatting errors in your XML document.

Here is an example of creating an XML document with a single root element using the DOM parser in Java:

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.newDocument();

Element rootElement = document.createElement("root");
document.appendChild(rootElement);

Element childElement = document.createElement("child");
rootElement.appendChild(childElement);

// ...

In this code, we create a new XML document with a single root element named "root". We then add a child element named "child" to the root element.

Conclusion

The 'org.w3c.dom.DOMException: Only one root element allowed' exception is a common error when working with XML documents in Java using the DOM parser. By ensuring that your XML document has only one root element, you can avoid this exception and create valid XML documents.