How to check if an element exists in the XML using XPath?

Solution 1:

Use the boolean() XPath function

The boolean function converts its argument to a boolean as follows:

• a number is true if and only if it is neither positive or negative zero nor NaN

• a node-set is true if and only if it is non-empty

• a string is true if and only if its length is non-zero

• an object of a type other than the four basic types is converted to a boolean in a way that is dependent on that type

If there is an AttachedXml in the CreditReport of primary Consumer, then it will return true().

boolean(/mc:Consumers
          /mc:Consumer[@subjectIdentifier='Primary']
            //mc:CreditReport/mc:AttachedXml)

Solution 2:

Use:

boolean(/*/*[@subjectIdentifier="Primary"]/*/*/*/*
                           [name()='AttachedXml' 
                          and 
                            namespace-uri()='http://xml.mycompany.com/XMLSchema'
                           ]
       )

Solution 3:

The Saxon documentation, though a little unclear, seems to suggest that the JAXP XPath API will return false when evaluating an XPath expression if no matching nodes are found.

This IBM article mentions a return value of null when no nodes are matched.

You might need to play around with the return types a bit based on this API, but the basic idea is that you just run a normal XPath and check whether the result is a node / false / null / etc.

XPathFactory xpathFactory = XPathFactory.newInstance(NamespaceConstant.OBJECT_MODEL_SAXON);
XPath xpath = xpathFactory.newXPath();
XPathExpression expr = xpath.compile("/Consumers/Consumer/DataSources/Credit/CreditReport/AttachedXml");
Object result = expr.evaluate(doc, XPathConstants.NODE);

if ( result == null ) {
    // do something
}