Question

I am parsing the xml file. I am always getting NullPointerException. Can anyone suggest me where I made a mistake?

<?xml version="1.0"?>
 <categories>
<category name="ABC">
    <subcategory name="windows" 
        loc="C://program files" 
        link="www.sample.com" 
        parentnode="Mac"/>
    <subcategory name="456" 
        loc="C://program files" 
        link="http://" 
        parentnode="ABC"/>
</category>

    <category name="XYZ"> 
        <subcategory name="android" 
            loc="C://program files" 
            link="www.sample.com" 
            parentnode="XYZ"/>
        <subcategory name="apple" 
            loc="C://program files" 
            link="http://abc.com" 
            parentnode="XYZ"/>
    </category>
</categories>

In the above xml file, I want to parse only the subcategory name android. For this, I made

NodeList catLst = doc.getElementsByTagName("category");

            for (int i = 0; i < catLst.getLength(); i++) {

                Node cat = catLst.item(i);

                NamedNodeMap catAttrMap = cat.getAttributes();
                Node catAttr = catAttrMap.getNamedItem("name");

                if (catName.equals(catAttr.getNodeValue())) { // CLUE!!!

                    NodeList subcatLst = cat.getChildNodes();

                    for (int j = 0; j < subcatLst.getLength(); j++) {
                        Node subcat = subcatLst.item(j);
                        NamedNodeMap subcatAttrMap = subcat.getAttributes();
                        Node subCatAttr = subcatAttrMap.getNamedItem("name");

                        if (subCatfound.equals(subCatAttr.getNodeValue())
                                && subcatAttrMap != null) {
                            Node subcatAttr = subcatAttrMap.getNamedItem(attrName);
                            list.add(subcatAttr.getNodeValue());
                        } else {
                            System.out.println("NULL");
                        }
                    }
                }

Whenever I do this, I am getting NullPointerException. Can anyone know where I made a mistake?

Answer 1

This code is a simplification of what you’re trying to trying to achieve:

public static Element getElementByNameAttribute(String elementName, String nameAttributeValue, Document doc) {
    if (elementName!= null && !elementName.isEmpty() && nameAttributeValue!= null && !nameAttributeValue.isEmpty()) {

        NodeList subCategoryList = doc.getElementsByTagName(elementName);
        for (int i = 0; i < subCategoryList.getLength(); i++) {
            Element element = (Element) subCategoryList.item(i);

            if (nameAttributeValue.equals(element.getAttribute("name"))) {
                return element;
            }
        }
    }

    return null;
}

If you put this in a class, e.g. DOMUtil (in my case), you can simply do this:

Element subCategoryAndroid = DOMUtil.getElementByNameAttribute("subcategory", "android", doc);

PS: This is untested.