Question

I am using the Document object to extract all the tags from an xml. If the xml has an empty tag, I get a null pointer exception. How do I guard against this? How do I check for an empty tag?

<USTrade>
<CreditorId>
<CustomerNumber>xxxx</CustomerNumber>
<Name></Name>
<Industry code="FY" description="Factor"/>
</CreditorId>
<DateReported format="MM/CCYY">02/2012</DateReported>
<AccountNumber>54000</AccountNumber>
<HighCreditAmount>0000299</HighCreditAmount>
<BalanceAmount>0000069</BalanceAmount>
<PastDueAmount>0000069</PastDueAmount>
<PortfolioType code="O" description="Open Account (30, 60, or 90 day account)"/>
<Status code="5" description="120 Dys or More PDue"/>
 <Narratives>
<Narrative code="GS" description="Medical"/>
<Narrative code="CZ" description="Collection Account"/>
</Narratives>
</USTrade>
<USTrade>

So, when I use:

                NodeList nm = docElement.getElementsByTagName("Name");
                if (nm.getLength() > 0)
                    name = nullIfBlank(((Element) nm.item(0))
                            .getFirstChild().getTextContent());

Nodelist gives a length of 1, because there is a tag, but when I do getTextContent(), it hits the null pointer because FirstChild() doesn’t return anything for tag = Name

And, I have done this for each xml tag. Is there a simple check I can do before every tag extraction?

Answer 1

The first thing I would do would be to unchain your calls. This will give you the chance to determine exactly which reference is null and which reference you need to do a null check for:

 NodeList nm = docElement.getElementsByTagName("Name");
                if (nm.getLength() > 0) {
                    Node n = nm.item(0);
                    Node child = n.getFirstChild();
                    if(child == null) {
                        // null handling
                        name = null;
                     }
                    else {
                       name = nullIfBlank(child.getTextContent());
                    }

                 }

Also, check out the hasChildNodes() method on Node! http://docs.oracle.com/javase/1.4.2/docs/api/org/w3c/dom/Node.html#hasChildNodes%28%29